French physicist and mathematician André-Marie Ampère (1775–1836) was one of the first scientists to study electromagnetism. His work followed the discovery made in 1820 by Danish physicist Hans Christian Ørsted that a magnetic needle is deflected by an adjacent electric current. Ampère found that two parallel wires carrying electric currents attract or repel each other, depending on whether the currents flow in the same direction (attracting) or opposite direction (repelling). He then devised a mathematical theory, which came to be called Ampère’s Law, to describe the relationship between electricity and magnetism. The SI unit of measurement of electric current—the rate at which a current flows round a circuit—the ampere (A), (amp for short), is named after him.
Mary Anning (1799–1847) was an English fossil-hunter and self-taught palaeontologist. A fossil discovered and excavated by Mary and her brother Joseph in 1810–11 was the first complete ichthyosaur fossil to be found, and it brought Mary to the attention of collectors and scientists in London. Amongst many other later finds was the first complete skeleton of the long-necked Plesiosaurus in 1824, and the flying reptile Pterodactylus in 1828. Despite not having any formal scientific training, Mary taught herself geology, anatomy and palaeontology, and became an expert on all aspects of her discoveries. As a woman, Mary Anning was not permitted to become a member of the newly formed Geological Society of London. Yet many palaeontologists sought her advice for their research.
The Greek mathematician, physicist, astronomer and inventor Archimedes (c. 287–212 BC) was one of the greatest scientists of the classical age. Among many inventions and mathematical advances, Archimedes calculated an accurate estimate of π (pi), the ratio between a circle's diameter and its circumference (edge). Pi is used today in many areas of mathematics, science and engineering. Archimedes is best known for what has become known as “Archimedes’ Principle”. He was given the task of determining whether a goldsmith was stealing gold during the making of a golden wreath, replacing it with a cheap—and less dense—alloy.
Archimedes took a bath and realised from the rise of the water when he got in that he could calculate the volume of the gold wreath by immersing it in a bath and measuring the amount of water it displaced. Now he could compare its volume with its mass and prove whether or not it was made entirely of gold. Archimedes leapt from his bath and went running naked through the streets shouting "Eureka!" ("I have found it!").
The Greek philosopher Aristotle (384–322 BC) made a massive contribution to many aspects of human knowledge, including physics, biology, astronomy, philosophy and even politics, poetry and music. Aristotle believed that our knowledge is based on direct observations of the world around us. This basic philosophy, called empiricism, was a shift away from that of his teacher, Plato (c. 427–347 BC), who believed that abstract thought could explain the nature of things. Many of Aristotle’s “laws of the universe” tended to come from simple observation and reason. But they were not always backed by sufficient facts or careful experimentation that modern scientific method demands before such laws could be accepted.
French physicist Henri Becquerel (1852–1908) was the discoverer of radioactivity, for which he won the 1903 Nobel Prize in Physics (sharing it with Marie and Pierre Curie). He had been researching X-rays—a phenomenon discovered in 1895 by the German physicist Wilhelm Röntgen (1845–1923). X-rays are like light, but have much shorter wavelengths and can pass through some solids. Becquerel wanted to investigate whether there was any connection between X-rays and naturally occurring phosphorescence. He found that the chemical compounds containing the element uranium also gave out rays, but which were different from X-rays—they could be deflected by electric or magnetic fields. These new rays left a foggy mark on a light-sensitive photographic plate. Becquerel could not explain why this had occurred. It was left to Marie Curie to establish that the radiation came from the uranium atoms in the compound, and for her to call the way they emitted rays “radioactivity”.
Niels BohrThe Danish physicist Niels Bohr (1885–1962) is best known for his work on understanding atomic structure. In his theory of 1913, Bohr combined Max Planck’s quantum theory with the work of Ernest Rutherford, who described the atom as a positively charged nucleus with negatively charged electrons orbiting around it. Bohr had the idea that electrons travel in clearly defined orbits. In order to jump between them, the electrons need to either give off or absorb specific amounts (quanta) of energy. This model is the one scientists accept today. Bohr’s work earned him the Nobel Prize in Physics in 1922. During World War II, he fled Denmark. He became a prominent member of the team of physicists working on the Manhattan Project in the US—the development of the atomic bomb. However, in later years Bohr campaigned for the peaceful use of atomic technology.
Jagadish Chandra Bose
Indian scientist Jagadish Chandra Bose (1858–1937) proved by experimentation that plants share many features in common with animals. Born in Bangalore, India, Bose studied physics at Cambridge University before returning to India. He successfully demonstrated that plants are also sensitive to heat, light and sound. Using an instrument called a Crescograph, he observed and recorded the minuscule responses of plants to external stimulants such as poison, fertilizers, light rays and radio waves. The instrument could multiply up movements in plant tissues by up to about 10,000 times. Other plant physiologists were able to support his findings years later, using more advanced instruments. Bose was elected Fellow of the Royal Society in 1920 for his achievements.
Anglo-Irish scientist Robert Boyle (1627–91) is famous for devising a law that would predict how a gas would behave at a certain temperature, volume and pressure. Called Boyle’s Law, it states that if the gas’s temperature remains unchanged, the pressure exerted by a mass of gas would be inversely proportional to the volume it occupies. So if the volume of the gas decreases, the pressure increases, or, if the volume remains the same and the temperature increases, the pressure also increases. Boyle was the first prominent scientist to perform controlled experiments and publish his work giving details of the procedures he followed, the apparatus he used and the observations he made—the scientific method.
Boyle, who considered chemistry to be the science of the composition of substances, was one of the founders of modern chemistry. He thought (correctly) that elements were composed of particles of various kinds and sizes. Among his achievements was introducing the litmus test as a way of telling acids from bases.
American biologist and conservationist Rachel Carson (1907–64) is famous for writing about global environmental issues. As a child she developed a great passion for nature through exploring the countryside near her family farm. She studied biology at Pennsylvania College for Women and zoology at Johns Hopkins University. She developed a passion for the ocean, and wrote a number of books, articles and radio scripts about marine life. In the 1940s and 50s, Carson became more and more concerned about the effects of chemicals and pesticides on the environment. Her most famous book, Silent Spring, was published in 1956. Focusing especially on the impact of the use of pesticides on birds, the book alerted the public to the dangers of damaging the environment. Rachel Carson died of cancer in 1964.
The Polish priest and astronomer, Nicolaus Copernicus (1473–1543), challenged the traditional view of his time that the Earth was stationary at the centre of the Universe with all the planets, Moon, Sun and the stars rotating around it. In his model of the Solar System, now known to be correct, the Sun lay at the centre of a system of orbiting planets. Only the Moon orbited the Earth. In his major work On the Revolutions of the Heavenly Spheres, completed around 1530, Copernicus put forward the theory that the Earth rotates daily on its axis and orbits yearly around the Sun. He also stated that the other planets circle the Sun. Copernicus did, however, wrongly believe that the planets’ orbits were perfect circles and that they moved in epicycles.
Francis Crick and James Watson
English scientist Francis Crick (1916–2004) and American scientist James Watson (born 1928) met in 1951 when Watson, then a student, joined Crick at the Medical Research Council Unit of the Cavendish Laboratory in Cambridge. They worked together on studying the molecular structure of DNA (deoxyribonucleic acid), the chemical that was thought to contain the genetic information for cells, although no one then knew this for sure. At the same time, Maurice Wilkins and Rosalind Franklin, both working at King's College, London, were using X-ray diffraction (a scientific method for discovering the structure of a crystal—see Rosalind Franklin, below) to study DNA. Crick and Watson relied on their findings for their own research.
James Watson in 2011In April 1953, Crick and Watson published their discovery. The molecular structure of DNA, they said, is a double helix: it has two strands that spiral around each other to form the shape of a twisted ladder. Crick and Watson’s model of DNA showed how a living thing’s genes (the information it needs to develop, grow and maintain itself through life) are coded on it. It also explained how DNA copies itself. Crick and Watson won the 1962 Nobel Prize in Medicine for their discovery of the structure of DNA. They shared their prize with Maurice Wilkins. Rosalind Franklin had died in 1958, so she could not be nominated. Their discovery was one of the most significant scientific discoveries of the 20th century.
Francis Crick moved to California in 1977, where he moved into brain research, becoming professor at the Salk Institute for Biological Studies in San Diego. He remained there for the rest of his life. From 1988 to 1992, James Watson directed the Human Genome Project at the American National Institutes of Health.
Marie Curie (1867–1934) was a pioneering scientist in an age when it was unusual for a woman to be a scientist at all. She is remembered today for her work with her husband Pierre Curie on radioactivity, especially the discovery of two radioactive elements, radium and polonium, and the use of radioactivity in the treatment of cancer. Marie Curie also played an important part in developing the use of X-rays, especially during World War I. She was the first woman to win a Nobel prize, and the only woman to have to have won in two different fields, physics and chemistry.
French zoologist and anatomist Georges Cuvier (1769–1832) is today considered the “father of palaeontology”. In Cuvier’s day, the idea of extinction—that creatures were simply wiped from the face of the Earth—was not generally accepted. When fossils of animals unlike anything alive were discovered, it was assumed they were alive somewhere in an unexplored part of the world. Cuvier was able to demonstrate convincingly that extinctions did occur. He showed that different rock strata (layers) of rock each contained fossils of living things, and that the lower a stratum was, the more different the fossil species it contained were from present-day ones.
Although his research supported Darwin’s theory of evolution, Cuvier himself rejected the idea. He believed that plants and animals were created for their particular roles and were unchanging throughout their existence. Over the course of history, he said, catastrophic events would kill off certain species, which were then replaced by new ones. Using his expert knowledge of the anatomy of modern mammals such as elephants (Cuvier was said to be able to reconstruct a skeleton based on a single bone), he showed that fossil mammoths differed from creatures currently alive.
The English scientist and mathematician John Dalton (1766–1844) is best known for his atomic theory, which laid the foundations of modern chemistry. In 1801, Dalton presented his findings about the nature of gases, stating, for example, that all gases could become liquids so long as their temperature was sufficiently low and their pressure sufficiently high. His study of gases led him to investigate what they were actually made of.
The idea of atoms had first been proposed more than 2000 years earlier by the ancient Greek scientist Democritus. Democritus believed that everything was made of tiny particles called atoms and that these atoms could not be divided up into smaller particles. Analysing the results of hundreds of chemical reactions, Dalton found Democritus to be correct.
In A New System of Chemical Philosophy, (published 1808), he proposed that the identical atoms of an element differ from those of all other elements, and that atoms of different elements have different masses. He represented these elemental atoms by circular symbols. Dalton also published diagrams showing, for example, how atoms combine to form molecules and how water molecules arrange themselves when they become frozen in ice.
Charles Darwin (1809–1882) was a British scientist whose work on evolution—the way living things change over generations—revolutionized scientific thinking. At the beginning of the 19th century, many people still believed the story of creation as told in the Bible. But scientists were already challenging this. Even Darwin’s own grandfather, Erasmus Darwin (1731–1802), had suggested that living things changed or evolved. The discovery of fossils of long-extinct animals threw up new evidence. But how living things might have undergone changes over millions of years was still a mystery. Darwin’s most famous work, On the Origin of Species, first published in 1859, occupied many years of his life, and suggested a ground-breaking solution.
Humphry Davy (1778–1829) was an English chemist best known for his experiments in electrochemistry and his invention of a miner's safety lamp. In 1800, the Italian scientist Alessandro Volta had introduced the first battery. Davy used this to carry out the process now known as electrolysis, in which he was able to separate a chemical compound into the molecules that make it up. In this way, Davy was thus able to “isolate” a number of elements for the first time: potassium and sodium in 1807 and calcium, strontium, barium and magnesium in 1808.
In 1815, Davy became aware of the dangers Newcastle miners faced from methane gas. The fires and explosions caused when methane seeped into the mine shafts and ignited by the miners’ lamps had resulted in many deaths. Davy invented a new kind of lamp (the “Davy lamp”) in which the flame was separated from the gas: the wick was enclosed inside a mesh screen. It originally burned vegetable oil. That same year, 1815, George Stephenson, the railway engineer, invented an alternative type of safety lamp.
Paul Ehrlich (1854–1915) was a German scientist who carried out pioneering research in the fields of haematology (the study of diseases of the blood), immunology (the study of the immune system) and chemotherapy (a treatment of diseases using drugs). After suffering from a severe bout of tuberculosis himself, Ehrlich decided to investigate bacterial toxins (poisons) and how they could be treated. He found that, when under threat from a certain toxin, cells grow extra parts that break off to become antibodies.
Using this discovery, Ehrlich, together with Emil Adolf von Behring, developed a serum that was used successfully to counter the disease diphtheria during an epidemic in Germany. In 1908 Paul Ehrlich shared the Nobel Prize in Physiology or Medicine for his work on the immune response.
Ehrlich later moved on to the study of chemotherapy, the use of chemicals in the treatment or control of a disease. He put forward the idea of “magic bullets”, substances that can seek out specific disease-causing microbes and destroy them. He achieved great success with this work—for example, in developing the medicine Salvarsan, an effective treatment against syphilis, in 1909.
Albert Einstein (1879–1955) was a German-born physicist who made some of the greatest contributions to modern science. He devised the equation E=mc2, linking mass and energy. Einstein thought that the Newtonian laws of motion, first proposed by Isaac Newton in the 17th century, could no longer hold true now that the laws of the electromagnetism were understood. This belief led to the development of his Special Theory of Relativity. He then realized that the principle of relativity could also be applied to understanding how gravity worked, and so he later developed the General Theory of Relativity. In 1921 Albert Einstein received the Nobel Prize in Physics.
English scientist Michael Faraday (1791–1867) rose from humble beginnings to become one of the greatest experimental physicists of all time. His work on the properties of electricity and magnetism revolutionized science and the technology that developed from it. He pioneered the electric motor and discovered how electricity could be generated. As a result of his work, electricity was transformed from a scientific curiosity into a powerful new technology.
Enrico Fermi (1901–54) was an Italian physicist, remembered for his work in nuclear physics, crucial to the development of the world’s first nuclear reactor. In 1938, Fermi won the Nobel Prize for Physics for his work on nuclear processes. Conducting experiments at Columbia University, New York, he showed that bombarding a uranium nucleus with neutrons could cause the nucleus to split into two, releasing numerous neutrons—along with massive amounts of energy. This was the first nuclear chain reaction. This work led directly to the development of the first atomic bomb, detonated at an airbase in New Mexico in 1945.
American physicist Richard Feynman (1918–88) is best known for his work in quantum electrodynamics (QED), a branch of science that combines quantum physics with electromagnetism. During World War II, he was one of the key figures in the Manhattan Project in the US, developing the atomic bomb. In 1950 he moved to the California Institute of Technology, where he spent the rest of his career. He shared the Nobel Prize for Physics in 1965. An enthusiastic popularizer of physics, he wrote a number of books, including Surely You’re Joking, Mr Feynman!, The Pleasure of Finding Things Out and—covering his own specialist field—Q.E.D: The Strange Theory of Light and Matter.
While serving as a medical captain during World War I, Scottish biologist Alexander Fleming (1881–1955) observed the terrible effects of deadly bacteria on patients. Later, in September 1928, Fleming noticed a ring of mould, a fungus, growing on one of the glass dishes of staphylococci bacteria that had been left out after research. On this dish alone, the area around the ring was free of bacteria. Fleming realised that the mould, which he identified as Penicillium notatum, had killed the bacteria. He had discovered the first antibiotic—later called penicillin—a substance that kills bacteria. It fell to two other scientists, Howard Florey and Ernst Chain, to develop penicillin so that it could be manufactured as a medicine. During World War II, penicillin saved the lives of thousands of wounded soldiers. In 1945 Fleming, Florey and Chain shared the Nobel Prize for Medicine.
American politician and scientist Benjamin Franklin (1706–1790) is famous for proving that lightning was a form of electricity. In June 1752 it is said Franklin attached a metal key to one end of a kite string and flew the kite in a stormy sky. Franklin took steps to ensure he was insulated, so that the electricity would not flow through his body and electrocute him. By showing that sparks jumped from the key to his hand, he proved that lightning was a form of electricity. His experiments lead to his invention of the lightning rod. Franklin was responsible for a number of other inventions. Among his many creations were bifocal glasses, a metal-lined fireplace called the Franklin Stove and the musical instrument known as the glass harmonica.
Rosalind Franklin (1920–58) was an English chemist. She made a crucial contribution to the understanding of the structure of DNA (deoxyribonucleic acid). Her work on X-ray diffraction images of DNA confirmed that the molecule had a shape of a double helix. X-ray diffraction is a scientific method for discovering the structure of a crystal. A crystal's atoms cause a beam of X-rays to diffract (spread out) in many different directions. By measuring the angles and intensity of the diffracted beams, scientists can produce 3D images showing the positions of the atoms making up the crystal.
Rosalind Franklin's work was shown in 1952—without her approval or knowledge—to biologist James Watson who at the time was working with Francis Crick on identifying the structure of DNA (see above). The evidence was crucial to Crick and Watson's success in discovering DNA's molecular structure. Crick, Watson and Rosalind's colleague Maurice Wilkins jointly received the 1962 Nobel Prize in Physiology or Medicine for their contributions to the discovery. But Franklin had died in 1958 and therefore could not be nominated.
Born in the Greek city of Pergamon, Galen (c. AD 130–200) was the most famous physician in the Roman Empire. His theories about the human body were accepted in the West for centuries after his death. Galen believed that dissection was crucial to the understanding the human body. Although he was forbidden by Roman law to dissect human corpses, the severe injuries that gladiators frequently received gave Galen plentiful opportunities to expand his knowledge of the insides of the human body.
Like Hippocrates, Galen always carefully examined his patients and recorded their symptoms. He paid particular attention to the patient’s pulse, using any abnormalities as a way to diagnose disease and prescribe treatments (feeling a patient’s pulse is still a standard medical procedure today).
Galen believed that the body carried three different kinds of blood, containing various “spirits”: the veins carried “natural spirit” from the liver, the arteries carried “vital spirit” from the lungs and heart, while the nerves delivered “animal spirit” from the brain. Galen’s ideas, though mistaken, were taken up by Islamic scholars. Their works, in turn, greatly influenced thinking in medieval Europe. It was only in the 16th century, when the dissection of human bodies was allowed, that anatomists started to realise that the human body worked in quite a different way.
The Italian scientist Galileo Galilei (1564–1642) is best remembered as an astronomer. His insistence that the Earth was not at the centre of the Universe and that, along with other planets, it orbits the Sun, brought him into conflict with the Catholic Church, because it challenged the biblical story of creation. Galileo was also a pioneer in the study of gravity and motion. Unlike many earlier scientists, Galileo based his theories on observation and experimentation—and making detailed records of his work—rather than on traditional beliefs. For this he is known as the Father of Modern Science.
Dame Jane Goodall (born 1934) is an English primatologist (an expert on primates). She is best known for her 45-year study of the lives of chimpanzees in Gombe Stream National Park, Tanzania. Goodall began her studies in 1960. She soon became aware that the apes had distinct personalities and formed relationships with each other. Her research also showed that chimpanzees were not only highly intelligent, they were also were tool-makers; at the time it was believed only humans could make and use tools. She observed a chimp carefully inserting twigs into a termite mound, then removing them—covered with termites, which it ate. Goodall also witnessed chimps, once thought to be vegetarian, participating in hunts for monkeys.
Edmond Halley (1656–1742) was an English astronomer and mathematician. He was the first person to calculate the orbit of the comet, later named after him. He realised that the three historic comets, observed in the years 1531, 1607 and 1682 were so similar in appearance in recorded sightings that they must have been the same object returning to the Earth’s skies every 75 or 76 years. He accurately predicted its return in 1758—although he did not live to witness it himself. Ever since it has been known as Halley's Comet. In 1716, Halley devised a method for using observations of the transits of Venus across the Sun’s disc to measure accurately the distance of the Earth from the Sun. In 1720, Halley became Astronomer Royal at Greenwich, a position which he held until his death.
English surgeon William Harvey (1578–1657) is best known for his demonstration of the circulation of the blood. Harvey's work is fundamental to the understanding of the role of the heart in the body. Yet his work was not immediately accepted, since it contradicted the theories behind blood-letting, which was central to medical practice of the time: many diseases were thought to be caused by an excess of blood in the body. Harvey had studied at Padua, Italy, and been influenced by the teachings of Galileo. Harvey's dissections of various animals, including humans, laid the basic foundations for the study of physiology, the study of how the body works. He showed how the blood circulated through the body, with the heart acting as pump for pushing blood—in one direction—through the network of arteries and veins.
English physicist and mathematician Stephen Hawking (1942–2018) is best known both for his work on the nature of black holes—and for being a long-term sufferer of ALS (amyotrophic lateral sclerosis), also known as Lou Gehrig’s disease, which has severely affected his movement and speech. He was first diagnosed with this disease while still a postgraduate at Cambridge in the 1960s. Since 1970 Hawking has studied the properties of black holes and the behaviour of matter near them. Black holes are created when huge stars collapse to zero size and infinite density, something known as a “singularity”. Hawking realised that the Big Bang (the massive explosion in which the Universe was born) was like a black hole in reverse—a key to helping understand to how the Big Bang occurred. In 1974 Hawking discovered that black holes emitted heat radiation.
In 1974 Stephen Hawking was elected as a fellow of the Royal Society. At the age of only 32, he is one of the youngest people to achieve that honour. A keen popularizer of his subject, cosmology, in 1988 Hawking published A Brief History of Time in 1988, which became an international bestseller. In his current research, he is attempting to combine work from quantum mechanics with relativity to give a unified quantum theory of gravity, a single theory that describes our Universe, the so-called “theory of everything”.
Hermann von Helmholtz
The German scientist Hermann von Helmholtz (1821–94) made important discoveries in a number of scientific fields, including physics, physiology and meteorology. At that time, some physiologists believed that living things were special because they contained some kind of “vital force”. But Helmholtz showed that all living things obeyed the same physical laws as everything else. He proposed the law of the conservation of energy: energy can neither be created nor destroyed but transforms from one form to another. Both German physicist Julius von Mayer (1814–78) and James Joule are also credited with this important law. Helmholtz also invented many new instruments to monitor how the body works, including the ophthalmoscope, for seeing inside the eye, in 1851. He used such devices to investigate how the senses work, for example, how we see colour and how we hear music.
American scientist Joseph Henry (1797–1878) is best known for his work in electricity and magnetism. In the 1830s he carried out several experiments on electromagnetism that were quite similar to those of Michael Faraday. Because Faraday published his findings before Henry did, credit for making the discovery of electromagnetic induction—which Henry had achieved independently in 1832—went to Faraday. Henry’s work on electromagnetism was important, however. He found that by winding more and more coils around an iron core produced a stronger electromagnetic field, an observation he put to good use when designing electromagnets that could lift heavy weights.
Henry found that with a high voltage battery, an electric current could be sent through a very long piece of wire. An electromagnet could be used to open and close a switch, known as a relay, to transmit an electric signal along the wire. A long telegraph line, many kilometres in length, could be made up of a number of much shorter lines, each individually linked and powered by relays. This discovery opened the way to the invention of the electric telegraph by Samuel Morse.
William Herschel (1738–1822) was a German-born British astronomer and composer. He is famous not only for his discovery of Uranus (1781), along with two of its moons Titania and Oberon (1787), but also for other important discoveries in astronomy, based on observations made through the telescopes he had built himself (one of his telescopes had eyepieces that gave it a magnifying power of 6450 times). In the 1770s, Herschel carried out a survey of the sky, recording new nebulae and star clusters. He put forward a theory of how stars evolved, and came up with a model for how the stars of the Galaxy were distributed. He was also the first astronomer to suggest that nebulae—previously thought to be made of luminous fluid—are composed of stars. It was Herschel who first coined the term “asteroids” for the band of millions of rocky fragments that orbit the Sun between Mars and Jupiter.
The 40-foot telescope constructed by William Herschel. A reflecting telescope, it was constructed between 1785 and 1789 at...Read More >>The 40-foot telescope constructed by William Herschel. A reflecting telescope, it was constructed between 1785 and 1789 at Observatory House in Slough, England. It had a 120-cm (470-inch) diameter primary mirror and a 12-metre-long focal length—hence the name "Forty-Foot". It may have been used to discover Enceladus and Mimas, two of the moons of Saturn.
Heinrich Hertz, a German physicist (1857–94) proved the existence of electromagnetic waves first predicted by James Clerk Maxwell. He acheived this in a series of experiments carried out in 1887. Hertz built a transmitter in which two copper rods, each attached to large zinc spheres, were separated by a small gap. He placed a receiver, a simple loop of copper wire which also had a tiny gap between its ends, 1.5 metres (5 feet) away. When he applied a high-voltage electric current to the transmitter, sparks jumped the gap, creating pulses of electricity in the wires. These pulses sent out electromagnetic waves—radio waves—through the air around the transmitter. Picked up by the receiver, the waves created a small spark in the gap. The unit of frequency of a radio wave—one cycle per second—is named the hertz in his honour.
The scientific approach to medicine was introduced by the ancient Greeks. Hippocrates (c. 460–370 BC) founded a school of medicine on the Greek island of Kos, where diagnosis of illness was based on thorough examination of patients, including making records about their condition. He believed that all diseases had a natural cause rather than a supernatural one, that is, caused by the gods. He also proposed that diet and exercise affected the human body. Such ideas led to Hippocrates being known as the Father of Medicine.
The English scientist, inventor, artist and architect Robert Hooke (1635-1703) is most famous for his pioneering work using the first microscopes. He was the first to use the term “cells” to describe the basic building blocks of life. He also invented or improved a number of scientific instruments, including the anchor escapement mechanism (used in a pendulum clock) and the balance spring (used in a pocket watch). His scientific studies extended across the disciplines of biology, chemistry and physics. As well as his ideas on gravity and fossilization, he put forward Hooke’s Law, which states that the tension force in a spring increases in direct proportion to the length it is stretched to.
Edwin Hubble (1889–1953) was an American astronomer. He is best known for his discovery of galaxies other than our own Milky Way Galaxy. Between 1925 and 1929, he discovered the existence of isolated masses of stars called galaxies that were too distant to be part of our own galaxy. Up until then, astronomers had believed that the Universe consisted of the Milky Way alone. Hubble also devised a method for classifying galaxies, using the terms “ellipticals”, “spirals” and “barred spirals” to describe their basic shapes. In 1929 he announced what has become known as Hubble’s Law: the farther away a galaxy is from another point in space, the faster it appears to move away as the Universe expands. Hubble’s Law adds weight to the belief that the Universe was created in the Big Bang and is continuing to expand uniformly.
Alexander von Humboldt
Alexander von Humboldt (1769–1859) was a German explorer and naturalist. He is best known for his works on botanical geography, laying the foundations of the new science of biogeography. Along with the botanist Aimé Bonpland (1773–1858), he travelled widely in South America between 1799 and 1804. Over the course of his travels, he compiled a list of Southern Hemisphere stars, observed a transit of Mercury across the Sun and collected samples of some 60,000 plants that grew at different altitudes and habitats.
Humboldt made a study of the various physical features, including Mount Chimborazo in Ecuador and the Orinoco River in Venezuela, he came across. He discovered a cold current of water flowing past the coast of Peru, known today as the Humboldt Current. Humboldt learned how the South American Indians prepared a poison—called curare—from plants, which they used to tip their arrows, and which paralysed their victims.
Later in life, Humboldt studied the Earth’s magnetism, noting that some rock types had different magnetic properties. He published all his scientific observations and findings in a work called Kosmos, the first volume of which was published in 1845.
Christiaan Huygens (1629–95) was a Dutch mathematician, physicist and astronomer. He first put forward the idea that light travelled as waves, and discovered centrifugal force. He is also known for his improvements to the design of telescopes along with his studies of the rings of Saturn and the discovery of its moon, Titan. After investigating the forces on bodies moving in circular paths, Huygens went on to invent the pendulum clock in 1656, increasing the accuracy of clocks enormously, from minutes to seconds per day.
For centuries, serious diseases went uncontrolled. Millions of people died from them. It was the discovery of a means to protect people against one such disease, smallpox, that began the modern era of medicine. Edward Jenner (1749–1823), an English country doctor, observed that milkmaids who caught a disease called cowpox from their cows never caught smallpox itself. Cowpox is similar to smallpox, but much milder, and produces pus-filled blisters on the hands. Jenner realised that infection with cowpox must be protecting the milkmaids from smallpox, and decided to test his theory. He took some pus from a milkmaid’s blister and scratched it into the arm of an eight-year-old boy. Within a few days, the boy developed mild cowpox. A few weeks later, Jenner infected the boy with smallpox—but he did not develop the disease. Jenner had "vaccinated" the boy against smallpox.
Jenner had developed vaccines—substances introduced into the bloodstream that protect people from serious disease. They are dead or weakened versions of germs that cause the disease—although Jenner himself was unaware of what germs were. The vaccine germs cannot themselves cause harm, but the body’s defence system fights and kills them. It will then recognize the germs again quickly in the future. It took until the 1840s before the medical establishment could accept the findings of a country doctor and adopt vaccination as a method of preventing disease.
English physicist James Joule (1818–89) is best known for his research into thermodynamics. In 1843 he calculated the amount of mechanical work needed to produce an equivalent amount of heat. But his findings challenged the view, widely held by physicists at the time, that heat was some kind of fluid. This view, which Joule had disproved, was known as the “caloric” theory of heat. With the support of William Thomson (later Lord Kelvin) and Michael Faraday, Joule’s theory gained acceptance by 1849. Thomson and Joule proceeded to carry out a number of experiments in the study of heat and energy, a field of physics that came to be known as thermodynamics. In one experiment, gases were observed to become cooler as they expanded, which became known as the Joule Thomson effect. It is the principle on which refrigeration is based. The SI unit for an amount of heat is named the joule in Joule's honour.
The German mathematician and astronomer Johannes Kepler (1571–1630) developed the laws of planetary motion. While still a student, Kepler came to the conclusion that Nicolaus Copernicus’s model of the Solar System, which had the Sun at its centre and all the planets (including Earth) orbiting it, was correct. He showed, using Tycho Brahe’s detailed observations, that the planets moved in elliptical, rather than perfectly circular, orbits. The shapes of their orbits also explained the “wandering” that so perplexed earlier observers, thus disproving the idea that the planets moved in what were called epicycles. Publishing his discovery in a work called Astronomia Nova (The New Astronomy) in 1609, Kepler was the first person to arrive at the completely correct view of the Solar System.
Kepler’s work provided the platform for Isaac Newton to discover the law of universal gravitation. In 1611 Kepler improved Galileo’s telescope design by using two convex lenses instead of one with a concave lens eyepiece and a single convex objective lens. This design, the new standard for refracting telescopes, enabled higher magnifications.
Known as the “father of modern chemistry”, Antoine-Laurent Lavoisier (1743–94) was a French chemist. He named the gases oxygen and hydrogen, and worked out the role oxygen played in combustion (burning). He compiled the first proper list of known elements and helped to reform the way chemicals were named. He also discovered that, although matter could change its form or its shape, its mass always remained the same. In so doing, Lavoisier completely changed the way chemistry was practised. Lavoisier also helped to develop the metric system in order to make weights and measures uniform throughout France.
Louis and Mary Leakey
The palaeoanthropologists Louis Leakey (1903–72) and Mary Leakey (1913–96) were famous for their work in the study of human evolution. Besides his many books and articles, Louis’s many discoveries of fossils and stone tools contributed much to the understanding of human origins. He strongly supported Darwin’s assertion that human evolution began in Africa, a controversial position at the time but now one that is now universally accepted. Searching for fossils in East Africa in 1959, Mary Leakey, Louis’s wife, found a skull with large teeth in deposits that also contained stone tools. This is now identified as that of the human ancestor Australopithecus boisei. Dated to 1.75 million years ago, it established the great age of human origins. Then, in 1961 she found remains of a large-brained hominid living at the same time as Australopithecus, but, according to Louis, the earliest member of the human genus, Homo. The Leakeys called it Homo habilis.
In 1976 and 1977, Mary made the most exciting find of her career. About 50 kilometres (30 miles) south of the Olduvai Gorge at a site called Laetoli in Tanzania, she and her team discovered well-preserved hominid footprints in volcanic rock. The fossil footprints seemed to match the fossil remains found close by that belonged to the species Australopithecus afarensis (2.9 to 3.5 million years ago).
Antonie van Leeuwenhoek
Antonie van Leeuwenhoek (1632–1723) was a Dutch draper and scientist. He is best known for his improvements to the newly-invented microscope and for his pioneering work in microbiology. While working in his draper's shop, van Leeuwenhoek became interested in glassmaking. Heating glass rods over a hot flame, he created long threads of glass, from which he fashioned tiny glass spheres. These spheres became lenses for simple microscopes; the smallest spheres provided the highest magnifications, capable of magnifying between 275 and 500 times.
Using his hand-made microscopes, van Leeuwenhoek was the first to observe and describe single-celled organisms (which he called "animalcules"), now known as micro-organisms. He was also the first to observe blood flow in capillaries (tiny blood vessels).
The Swedish scientist, Carl Linnaeus (1707–78), is famous for devising the two-part naming system, known as binomial nomenclature, used to classify all living things. A chimpanzee's name under the Linnaean classification system, for example, is Pan troglodytes; a weeping willow is Salix babylonica. Linnaeus has been described as the father of taxonomy, the science of grouping living things together on the basis of their shared characteristics. He is also responsible for describing and classifying the human species exactly in the same way as he classified other animals, at a time when it was generally thought that humans should be regarded as a special case—quite different from animals.
Inspired by Pasteur's work, British surgeon Joseph Lister (1827–1912) carried out investigations into how germs (micro-organisms) could be killed. He knew that while people often survived surgical operations, many died on the wards afterwards. He realised that germs in the air were infecting patient’s wounds, causing them to get other diseases, such as gangrene—the death of body tissue as a result of infection. In 1865 he came up with the idea of using carbolic acid (phenol) to keep wounds clean during surgery. He then experimented with hand-washing, sterilizing surgical instruments and spraying carbolic acid in the theatre while operating. Death rates from his operations fell from more than 45% to 15%.
English mathematician Ada Lovelace (1815–52) is best known for her pioneering work in computer science. In her Notes of 1843, accompanying an article explaining how Charles Babbage's Analytical Engine, a device designed to perform calculations using punched cards (but never actually built) would work, Lovelace wrote about her belief that such a machine had the potential to perform much more elaborate functions than simply making mathematical calculations—just as modern computers do today. She demonstrated this by completing a program for the Analytical Engine: a method for calculating a certain mathematical sequence. Effectively, she had written the world's first algorithm, a step-by-step procedure for calculations. Ada Lovelace is today considered the world's first computer programmer.
Sir Charles Lyell (1797–1875) was a Scottish geologist and friend of Charles Darwin. Having taken up the position of Professor of Geology at King’s College London in the 1830s, he wrote three major books, including Principles of Geology (1830–33). In it he stated that geological processes observed taking place on Earth today could explain finds from the past. Charles Darwin was much influenced by Lyell’s idea that small geological changes built up over time, eventually leading to significant change. As a devout Christian, Lyell initially rejected Darwin’s theory of evolution—although he did eventually come round to supporting the idea of natural selection in biology.
James Clerk Maxwell
Scottish physicist James Clerk Maxwell (1831–79) was best known for developing electromagnetic theory. He wrote his first scientific paper at the age of 14, which was presented to the Royal Society of Edinburgh (although he was too young to be allowed to present it himself). In 1859, Maxwell suggested that Saturn’s rings were made up of a vast number of independently orbiting particles which were arranged in a series of narrow rings—a prediction proved correct by images sent back by Voyager 2 in 1980. The following year, Maxwell took up a post at King’s College, London. It was there that he proposed the kinetic theory of gases, in which he showed a gas’s temperature was determined by the motion of its molecules.
Later, following up on the ideas of Michael Faraday, Maxwell showed that electricity and magnetism were linked together as a single force, the electromagnetic force, and that this could be described in terms of an electromagnetic field. In his Treatise on Electricity and Magnetism, published in 1873, he calculated that an electromagnetic field travelled at the speed of light, and that therefore light itself must also be an electromagnetic wave. Maxwell predicted that infrared and other, as yet undiscovered electromagnetic rays, would also travel at the speed of light. (We now know that these other rays, such as radio waves, microwaves, UV and X-rays, all forms of electromagnetic radiation, do indeed travel at the speed of light.)
In 1865 the Czech friar and scientist Gregor Mendel (1822–1884) published his research into pea plants. His work showed how certain characteristics, or traits, were passed on from one generation to the next. Mendel concluded traits were inherited in predictable patterns. By cross-breeding plants over many generations, Mendel discovered that certain traits appeared in the offspring without any blending of parent traits. For example, if Mendel bred together a pea plant with purple flowers and one with white flowers, the offspring would be either purple or white—but never a lilac mix of the two colours. Each trait must have been determined by "units" that were passed on from just one parent to its offspring unchanged. These units are today known as genes.
The Periodic Table of elements is a list of all known elements arranged in order of their atomic numbers (the number of protons in each atom). It was designed by Russian chemist Dmitri Mendeleev (1834–1907), while he was writing a chemistry textbook. Mendeleev arranged the elements known at the time in order of their atomic mass (the total number of protons and neutrons in an atom). He placed groups of elements that had similar chemical properties into vertical columns in his table. This resulted in some gaps in his horizontal rows or “periods”, but Mendeleev decided that these gaps would eventually be filled by elements that had not yet been discovered.
Mendeleev could even work out the atomic mass for these missing elements and thus predict their properties. When the element gallium was discovered in 1875, its properties were found to be close to his predictions, and was duly placed in the gap below aluminium in his table. Two other predicted elements, germanium and scandium, were later discovered, further proving Mendeleev right.
Mendeleev had some problems ordering the elements according to their atomic mass. In order to place iodine in the same group as other elements with similar properties (e.g. fluorine, chlorine and bromine) Mendeleev had to put it after tellurium, so breaking his own rules—tellurium has a higher atomic mass than iodine. But using the atomic number instead of atomic mass as the organizing principle (first proposed by the British chemist Henry Moseley in 1913) solved the problem—iodine has a higher atomic number than tellurium. In fact, in most cases the two, atomic mass and atomic number, result in the same order.
English scientist Sir Isaac Newton (1642–1727) lived during an exciting period of history, known as the Age of Enlightenment, where many ideas we take for granted today were being put forward for the first time. This explosion of scientific research has been described as the Scientific Revolution. Newton's contribution included greatly furthering our understanding of the laws of motion, how gravity works and the nature of light and colour. Although modern physics explains matter and energy in a very different way, many of Newton’s ideas are still useful today, and have provided the basis for modern science.
Alfred Nobel (1833–96) was a Swedish chemist and the inventor of dynamite and gelignite. He was interested in the safe manufacture and use of nitroglycerine, a highly unstable explosive. in 1863, Nobel found that mixing nitroglycerine with silica (silicon dioxide) made it safer and easier to manipulate. He called this mixture dynamite. Twelve years later, Nobel invented an even safer explosive, made from dissolving a substance called nitrocellulose in the nitroglycerine and mixing it with potassium nitrate and wood pulp. Nobel named this new explosive substance gelignite.
The businesses Nobel set up to manufacture explosives in the 1870s and 1880s made him a fortune. In 1895 he set aside most of it to establish annual prizes in Physics, Chemistry, Medicine, Literature and Peace. An Economics Prize was added later. Called the Nobel Prize, they are the most prestigious prizes in science.
Hans Christian Ørsted
In 1820, the Danish scientist Hans Christian Ørsted (1777–1851) discovered that if an electric current passes through a wire coil, it creates a magnetic field around it. The magnetic field pushed a compass needle away from it—like magnetic poles always repel one another—making it swing around the wire in a circle. Temporarily, the wire coil became a magnet and the magnetic force acted in circles around the wire. Ørsted realised that the electric current had produced magnetism: he had discovered electromagnetism.
Louis Pasteur (1822–1895) was a French chemist and microbiologist, best known for his work on studying disease-carrying microbes (micro-organisms). These are the tiny, single-celled creatures, such as bacteria, that we sometimes call germs. He discovered that microbes were responsible for turning wine, beer and milk sour, and that they could also spread diseases. Before Pasteur's research, it was believed that these organisms could appear suddenly out of nowhere, but he proved that they already exist in the air. Pasteur’s work led to a change in medical procedures, in which hospitals and operating theatres were kept as clean as possible, so saving millions of lives.
German physicist Max Planck (1858–1947) is famous for proposing quantum theory. In 1900 Planck put forward the idea that energy is radiated not continuously, as was generally accepted at the time, but in discrete “bundles” called quanta (plural of quantum). A quantum of light energy, for example, is called a photon. Light consists of a stream of photons. (Describing light as photons explains how light can be absorbed and re-emitted by atoms). Planck’s ideas were adopted by Albert Einstein and others, leading to the establishment of what came to be known as quantum physics. Planck won the 1918 Nobel Prize in Physics for his work. Planck’s quantum theory has completely changed scientists’ understanding of atomic and subatomic processes.
English chemist and theologian Joseph Priestley (1733–1804) is noted for his work on the chemistry of gases, in particular the discovery of oxygen, which he called “dephlogisticated air”. Before him, scientists thought that the air consisted of just carbon dioxide and hydrogen. Besides the addition of oxygen, Priestley also identified the presence of nitrogen and other gases. Priestley discovered several important chemicals, including hydrochloric acid, nitrous oxide (laughing gas) and sulphur dioxide. He became the first person to isolate ammonia gas. He also invented soda water. Increasingly at odds with the government over his religious views and his support for the French Revolution, Priestley fled to the United States in 1794, where he died 10 years later.
X-rays were discovered—accidentally—by German physicist Wilhelm Röntgen (1845–1923) in 1895. He found that a piece of cardboard coated with crystals of the salt barium platinocyanide glowed when a thermionic valve or vacuum tube (an early electronic device) was switched on in the same room, even when the tube was covered over with opaque cardboard. Röntgen guessed these mystery rays—to which he gave the temporary name X-rays because he did not know what they were—came from the tube. It was soon discovered that the invisible rays could pass through many materials, such as flesh, but not through metal or bone. Röntgen found that X-rays could expose photographic plates, and made the first X-ray photograph of his wife’s hand in December 1895.
New Zealand-born physicist Ernest Rutherford (1871–1937) is best known for his pioneering work in nuclear physics. Between 1898 and 1907, while working with chemist Frederick Soddy at McGill University, Montreal, Canada, he investigated the newly-discovered phenomenon of radioactivity. He demonstrated that the atoms of some heavy elements—for example, uranium—naturally decay into slightly lighter, and chemically different, atoms. Rutherford proposed that radioactivity results from this disintegration of atoms. He reported the existence of what he termed alpha and beta particles in radiation given off by this process (the alpha particle was later found to be identical to the nucleus of a helium atom, the beta particle to an electron). It was for these discoveries that Rutherford was awarded the Nobel Prize in Chemistry in 1908.
In 1907, Rutherford moved to England to become Professor of Physics at Manchester University. There he discovered that the atom has a very small, heavy core at its centre, the nucleus (containing nearly the total mass of the atom), with a positive electrical charge. The nucleus is surrounded by a cloud of electrons, which had a negative electrical charge. This is the nuclear model of the atom, which is how we see the atom today. It replaced the “plum pudding” picture of an atom put forward earlier by J.J. Thomson.
In 1917, Rutherford discovered that the nuclei of certain elements, such as nitrogen, could be “broken up” by the impact of alpha particles coming from some radioactive source, such as the element radium. The nitrogen atoms were converted to oxygen atoms. During this process, high energy protons were emitted. Rutherford had succeeded in splitting the atom. This was the first artificially induced nuclear reaction.
English physicist Joseph John Thomson (1856–1940) is best known for his discovery of the electron, the first subatomic particle, in 1897. At the time, it was already known that atoms could exist as ions, carrying positive or negative charges. But atoms were still thought to be indivisible; they were thought to be the fundamental building blocks of all matter. Thomson discovered the electron when studying cathode rays. These mysterious rays were observed flowing inside cathode ray tubes, glass tubes that had most of the air inside removed, with a cathode (negative) electrode at one end and an anode (positive) electrode at the other. He realised that the particles making up cathode rays were about 1000 times smaller than atoms, that the particles were negatively charged, and that the particles were always of the same mass and charge.
Based on his results, Thomson went on to produce what is known as his “plum pudding” model of the atom. The atom was the positively charged “pudding” within which the electrons, “the plums”, orbited. (This was, in fact, an incorrect model: with protons and neutrons yet to be discovered, scientists still had no understanding of atomic structure.) In 1906 J.J. Thomson was awarded the Nobel Prize for Physics for his discovery. His son George also won the Nobel Prize in 1937—also for work with electrons, which he proved could behave like waves.
William Thomson, Lord Kelvin
Irish physicist and mathematician William Thomson (1824–1907), later known as Lord Kelvin, is best known for developing a temperature scale based on absolute zero, named the Kelvin scale. In 1846 he estimated the age of the Earth to be around 100 million years, basing his calculation on the temperature of the Sun and the rate of cooling for a body of the size of the Earth. He defended this calculation throughout his life, dismissing Darwin’s theory of evolution on the grounds that it would be impossible in this time period. (It is now known the Earth is 4.6 billion years old.)
In 1851 Thomson published ideas that would lead to the second law of thermodynamics—that heat will naturally flow from a hotter to a colder body—and supported his friend James Joule’s work on the nature of heat and energy. Together, they disproved the notion that heat was some kind of fluid, stating (correctly) that heat was the energy of motion of molecules. The term “kinetic energy” was coined by Thomson in 1856. Thomson was chief consultant for the laying of the first transatlantic telegraph cable (1857–58).
Italian physicist and mathematician Evangelista Torricelli (1608–1847) is best known for his invention of the mercury barometer. Galileo had observed that water could not be raised by more than height of around 10 metres (33 feet) using a suction pump. He believed, wrongly, that this was due to a “force created by a vacuum”. In an experiment he carried out in 1643, Torricelli proved that air had weight and could thus exert pressure. It is this pressure, also called atmospheric pressure, that determines the height to which a liquid will rise in a tube inverted over a basin containing the same liquid; the weight of the air presses down on the liquid forcing it up the tube to a certain height. In his experiment, Torricelli used mercury (some 14 times denser than water) to fill a tube about a metre (3.3 feet) long, sealed at the top. He placed the tube vertically in a basin of mercury. The column of mercury fell to about 76 centimetres (30 inches), leaving a vacuum above. The column's height changed when the atmospheric pressure increased or decreased. This was the first barometer.
New oceanic crust forms continuously at the mid-ocean ridge as magma pushes up from beneath the Earth’s crust and erupts as lava....Read More >>New oceanic crust forms continuously at the mid-ocean ridge as magma pushes up from beneath the Earth’s crust and erupts as lava. The lava cools, turning into rock (basalt), which forms the sea floor. As new lava erupts, the rock slowly moves away from the ridge. This is called sea-floor spreading. The farther it lies from the ridge, the older the rock: a) 5 million years ago b) 2–3 million years ago c) present day. The magnetic polarity—either normal or reversed—is preserved in the rock as it was formed.
Fred Vine and Drummond Matthews
British geologists Fred Vine (born 1939) and Drummond Matthews (1931–97), along with Canadian geophysicist Lawrence Morley (1920–2013), provided the crucial evidence of plate tectonics that would support Alfred Wegener’s theory of continental drift (see below).
Vine and Matthews used results from a survey of the Northern Indian Ocean floor to confirm two theories that explained how plate tectonics works. The first is that the ocean floor rocks are formed from volcanic eruptions at mid-oceanic ridges, which move away as if on a conveyor belt as new eruptions take place, a process called “sea-floor spreading”.
The second is that the Earth’s north and south magnetic poles swap places repeatedly every few hundred thousand years, each time reversing the direction of the Earth’s magnetic field, or polarity. The direction of this magnetic polarity—normal or reversed—is “frozen” into the volcanic lavas as they cool to form the basalt rock of the ocean floor. Over time, as the sea floor spreads, a sequence of alternating magnetic “stripes” over the ocean basins emerges. The data in the study carried out by Vine and Matthews clearly showed the existence of these patterns. Plate tectonics, the engine that drives continental drift, was a reality.
Alessandro Volta (1745–1827) was an Italian scientist, best known for inventing the battery. In 1771 another Italian scientist Luigi Galvani (1737–98) began a series of experiments in which he caused muscular contractions in a frog's legs by touching its nerves with different metals. He concluded that animal tissue itself must contain a vital force which he termed "animal electricity". He believed it to be a new form of electricity, one that flowed through the body as an "electrical fluid". Volta doubted that the electricity came from animal tissue, so, in order to disprove Galvani's theory, he invented a device known as the voltaic pile in around 1800.
Constructed from alternating discs of zinc and copper, each separated by pieces of cardboard soaked in brine, the voltaic pile produced a steady electric current. It showed that "animal electricity" could be produced using non-living materials. The voltaic pile was the world's first battery.
Wegener’s reconstruction (1922) of the Earth’s continents at three different stages in its history: late Carboniferous...Read More >>Wegener’s reconstruction (1922) of the Earth’s continents at three different stages in its history: late Carboniferous (Jung-Karbon), Eocene (Eozän) and early Quaternary (alt-Quartär). The shaded parts of the continents show the shallow seas which, at various times, covered what is now dry land.
Alfred Wegener (1880–1930) was a German astronomer and meteorologist. He is best known for proposing the theory of continental drift—the idea that Earth’s continents move. Studying a world map in 1910, Wegener noticed how the coastlines of eastern South America and western Africa seemed to fit together, rather like jigsaw pieces. After further research, he discovered that fossils of the same prehistoric species had been found in both Brazil and western Africa—evidence that South America and Africa may once have been linked. He later also found evidence of matching rock formations on the two continents.
In 1915, Wegener came up with the theory that many millions of years ago Earth had consisted of a single great continent, or “supercontinent”, which he called Pangaea. Very slowly, parts of Pangaea had begun to break up and move apart to form the continents we see today.
Despite the abundant fossil and rock evidence Wegener compiled between 1911 and 1929, the theory was rejected by most other geologists. It became accepted only in the 1960s, when plate tectonics became widely understood.
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