Science

100 Best Scientific Discoveries That Changed the World

100 scientific discoveries in order, from Eratosthenes measuring Earth to CRISPR and gravitational waves, with who found each one, when, and why it mattered.

By BlogAI Editors · · 29 min read

Science moves forward in small steps, but every so often a discovery changes what people believe, what doctors can treat or what engineers can build. This list covers 100 of those turning points in roughly chronological order, from the first measurement of Earth's size more than 2,000 years ago to genome editing and images of black holes.

For each discovery you will find who made it, when, what they actually found, and why it changed the world. The list spans astronomy, physics, chemistry, biology, medicine and Earth science.

How we chose them. "Best" is a judgement, not a measurement. We picked discoveries that either overturned a major idea, opened a new field, or led directly to technologies and treatments that affect daily life. We focused on discoveries, findings about how nature works, rather than inventions, although some (such as the transistor) were both. Dates are given as the year a result was published or announced, and many discoveries took years and many people. Nobel Prize years are included where they apply, and sources are listed under References.

Ancient and early modern science (to 1760)

Before modern laboratories, careful observation and mathematics were already revealing how nature works (OpenStax Astronomy 2e, chapter 2).

1. The size of Earth (Eratosthenes, about 240 BCE)

Greek scholars already knew Earth was round. Eratosthenes, librarian at Alexandria, noticed that at noon on the summer solstice the Sun shone straight down a well in Syene but cast shadows in Alexandria. Using the shadow angle and the distance between the cities, he estimated Earth's circumference. Depending on which length of "stadion" he used, his answer was within roughly 2 to 16 percent of the true value. It showed that geometry could measure the world.

2. Buoyancy (Archimedes, about 250 BCE)

Archimedes worked out that an object in a fluid is pushed up by a force equal to the weight of the fluid it displaces. The principle explains why ships float, how hot-air balloons rise and how submarines dive. It remains one of the oldest laws of physics still used unchanged by engineers.

3. A Sun-centred solar system (Copernicus, 1543)

Nicolaus Copernicus's On the Revolutions of the Heavenly Spheres placed the Sun, not Earth, near the centre of the planets' orbits. It explained the planets' apparent backward loops more naturally and began the Scientific Revolution, though it took the work of Kepler and Galileo to win the argument.

4. Accurate human anatomy (Vesalius, 1543)

Andreas Vesalius published On the Fabric of the Human Body, based on his own dissections of human bodies. It corrected many errors handed down from the ancient physician Galen, who had relied heavily on animal dissections, and established direct observation as the foundation of medicine.

5. Moons orbiting Jupiter (Galileo, 1610)

Turning an improved telescope to the sky, Galileo Galilei saw mountains on the Moon, countless stars in the Milky Way, and four moons circling Jupiter. Here was clear evidence that not everything orbits Earth. His later observations of the phases of Venus strongly supported the Sun-centred model.

6. Laws of planetary motion (Kepler, 1609–1619)

Using Tycho Brahe's precise observations, Johannes Kepler showed that planets move in ellipses, sweep out equal areas in equal times, and have orbital periods linked to their distances from the Sun. His three laws turned astronomy into a precise, predictive science and gave Newton the pattern his theory of gravity had to explain.

7. The circulation of blood (William Harvey, 1628)

Harvey showed by experiment and calculation that the heart pumps blood in a continuous loop through arteries and veins, rather than the liver constantly making new blood as had been believed. His work founded modern physiology and made later advances in cardiology and surgery possible.

8. Air has weight (Torricelli, 1643)

Evangelista Torricelli filled a glass tube with mercury, turned it upside down in a dish, and found that the column always settled at about 76 centimetres. He explained that the weight of the atmosphere was holding it up. He had invented the barometer and shown that air pressure is real and measurable, the basis of weather forecasting.

9. Cells (Robert Hooke, 1665)

In his book Micrographia, Hooke described the tiny box-like compartments he saw in thin slices of cork under a microscope and called them "cells". He was seeing the empty walls of dead plant cells, but the name stuck, and the cell became the basic unit of biology.

10. Microorganisms (Antonie van Leeuwenhoek, 1670s)

Using single-lens microscopes he made himself, Leeuwenhoek, a Dutch cloth merchant, saw and described tiny living creatures in pond water, rainwater and scrapings from his teeth. He was the first person to observe bacteria and protists, revealing a whole living world that would later prove central to disease, food and ecology.

11. Light has a speed (Ole Rømer, 1676)

Rømer noticed that eclipses of Jupiter's moon Io came earlier when Earth was approaching Jupiter and later when it was moving away. He concluded that light takes time to travel across Earth's orbit. Light was not instantaneous, and its finite speed later became a cornerstone of physics.

12. White light is a mixture of colours (Isaac Newton, 1672)

Using prisms, Newton showed that white sunlight splits into a spectrum and that a second prism can recombine the colours into white. Colour, he concluded, is a property of light itself, not something the prism adds. This founded the science of optics and, much later, spectroscopy.

13. Universal gravitation and the laws of motion (Isaac Newton, 1687)

Newton's Principia set out three laws of motion and showed that the same force that makes an apple fall keeps the Moon in orbit. A single set of equations explained tides, planetary orbits and falling objects. Newtonian mechanics still sends spacecraft to other planets.

14. A system for naming living things (Carl Linnaeus, 1735)

Linnaeus's Systema Naturae sorted living things into nested groups, and he later popularised the two-part Latin names, such as Homo sapiens, still used today. A shared naming system let naturalists around the world compare species, and the nested groups later made sense in light of evolution.

15. Lightning is electricity (Benjamin Franklin, 1752)

Franklin proposed that lightning is a giant electric spark, and experiments with a kite and with tall rods in France confirmed it in 1752. He invented the lightning rod, one of the first practical inventions to come directly from scientific research, which has protected buildings ever since.

The chemical and industrial revolutions (1770–1860)

Chemistry became a precise science, and physics revealed the links between electricity, magnetism and energy (OpenStax Chemistry 2e).

16. Oxygen (Scheele, Priestley and Lavoisier, 1770s)

Carl Wilhelm Scheele and Joseph Priestley independently isolated a gas that made flames burn brighter, Priestley publishing first in 1774. Antoine Lavoisier recognised it as an element, named it oxygen and used it to explain burning and breathing. This overturned the old phlogiston theory of combustion.

17. Conservation of mass (Antoine Lavoisier, 1780s)

By carefully weighing everything before and after reactions in sealed vessels, Lavoisier showed that mass is neither created nor destroyed in a chemical reaction. His 1789 Elementary Treatise on Chemistry also introduced a modern list of elements and naming system. Chemistry became a quantitative science.

18. Vaccination (Edward Jenner, 1796)

Jenner tested the folk observation that milkmaids who caught cowpox seemed protected from smallpox. He inoculated a boy with cowpox material and showed he was then protected against smallpox. Vaccination spread worldwide, and in 1980 the World Health Organization declared smallpox eradicated, the first human disease wiped out (WHO).

19. Deep time (James Hutton, 1788)

Studying rock layers in Scotland, Hutton argued that slow, everyday processes such as erosion and sedimentation, acting over immense periods, had shaped the land. His idea that Earth was vastly older than a few thousand years laid the groundwork for modern geology and gave evolution the time it needed.

20. The electric battery (Alessandro Volta, 1800)

Volta stacked discs of zinc and copper separated by brine-soaked cloth and produced a steady electric current. The voltaic pile was the first reliable source of continuous electricity, and it immediately enabled new discoveries, including splitting water into hydrogen and oxygen and isolating new elements such as sodium and potassium.

21. The wave nature of light (Thomas Young, 1801–1803)

Young passed light through two narrow openings and saw a pattern of bright and dark bands, which could only be explained if light behaved as a wave whose peaks and troughs added up or cancelled. The double-slit experiment later became the central demonstration of quantum physics.

22. Atomic theory (John Dalton, 1803–1808)

Dalton proposed that each element is made of identical atoms with a characteristic weight, and that compounds form when atoms combine in simple whole-number ratios. This explained why chemicals always combine in fixed proportions and gave chemists a way to think about reactions at the level of particles.

23. Electricity makes magnetism (Hans Christian Ørsted, 1820)

During a lecture, Ørsted noticed that a compass needle swung when a nearby wire carried current. Electricity and magnetism were linked. Within months, André-Marie Ampère had worked out the mathematics, and the electric motor followed soon after.

24. Organic chemicals can be made in the lab (Friedrich Wöhler, 1828)

Wöhler made urea, a compound found in urine, from inorganic starting materials. Many believed that substances made by living things needed a special "vital force". His result, and many after it, showed that the chemistry of life follows the same rules as all chemistry, opening the way to synthetic medicines, dyes and plastics.

25. Electromagnetic induction (Michael Faraday, 1831)

Faraday showed that moving a magnet near a coil of wire, or changing the current in a nearby coil, produces an electric current. This principle is behind almost every electric generator and transformer, so nearly all the electricity in the world's power grids is produced by induction.

26. Ice ages (Louis Agassiz, 1837–1840)

Agassiz argued that boulders far from their source, scratched bedrock and U-shaped valleys across Europe were the work of vast ice sheets that had once covered much of the continent. The idea that Earth's climate had changed dramatically in the past became a starting point for climate science.

27. Cell theory (Schleiden, Schwann and Virchow, 1838–1855)

Matthias Schleiden concluded that all plants are made of cells, and Theodor Schwann extended this to animals. Rudolf Virchow later popularised the principle that every cell comes from a pre-existing cell. Cell theory unified biology and showed that disease begins with changes in cells.

28. Conservation of energy (Mayer, Joule and Helmholtz, 1840s)

Julius von Mayer, James Prescott Joule and Hermann von Helmholtz showed that heat, motion, electricity and chemical energy can turn into one another but that the total is always conserved. Joule measured how much mechanical work produces a given amount of heat. The law is now one of the foundations of all of physics.

29. Surgical anaesthesia (William Morton, 1846)

On 16 October 1846 in Boston, dentist William Morton gave ether to a patient while a surgeon removed a tumour from his neck, and the patient felt no pain. Within months, anaesthesia was in use around the world. Long and delicate operations became possible for the first time.

30. Handwashing prevents infection (Ignaz Semmelweis, 1847)

In a Vienna hospital, Semmelweis noticed that women attended by doctors who had come from autopsies died of childbed fever far more often than those attended by midwives. When he required doctors to wash their hands in chlorinated lime, deaths fell sharply. His work was ignored at the time but is now recognised as a pioneering step in infection control.

31. Cholera spreads through water (John Snow, 1854)

During a cholera outbreak in London's Soho, Snow mapped the deaths and showed that they clustered around a water pump on Broad Street. He compared households supplied by different water companies and found far more deaths among those using sewage-contaminated water. His work founded modern epidemiology and led to clean-water systems.

32. Gases that trap heat (Eunice Foote, 1856, and John Tyndall, 1859)

Foote found that a glass cylinder filled with carbon dioxide heated up more in sunlight than one containing ordinary air, and suggested that more carbon dioxide would warm the planet. Tyndall soon measured precisely how water vapour and carbon dioxide absorb infrared radiation. Together their work is the physical basis of the greenhouse effect (NOAA Climate.gov).

33. Evolution by natural selection (Charles Darwin and Alfred Russel Wallace, 1858–1859)

Darwin and Wallace independently concluded that species change over generations because individuals with helpful inherited traits tend to survive and reproduce more. Their joint papers were read in 1858, and Darwin's On the Origin of Species followed in 1859. Evolution became the unifying theory of biology.

34. Spectroscopy reveals what stars are made of (Kirchhoff and Bunsen, 1859–1860)

Gustav Kirchhoff and Robert Bunsen showed that each element gives off and absorbs light at its own set of colours. Dark lines in the Sun's spectrum matched the patterns of elements on Earth, revealing the chemistry of the Sun. In 1868 a new line in sunlight revealed helium, found in the Sun before it was isolated on Earth in 1895.

Medicine, atoms and fields (1860–1900)

The second half of the nineteenth century revealed germs, genes, the periodic table and invisible radiation (OpenStax Microbiology).

35. Germ theory of disease (Louis Pasteur and Robert Koch, 1860s–1880s)

Pasteur showed that microbes cause fermentation and spoilage and do not arise spontaneously, and developed pasteurisation and new vaccines. Koch proved that specific bacteria cause specific diseases, identifying the causes of anthrax (1876) and tuberculosis (1882). Germ theory transformed medicine, sanitation and food safety.

36. Antiseptic surgery (Joseph Lister, 1867)

Inspired by Pasteur, Lister used carbolic acid to clean wounds, instruments and dressings. Deaths from infection after surgery fell dramatically in his wards. Antiseptic and, later, sterile techniques made surgery far safer.

37. Light is an electromagnetic wave (James Clerk Maxwell, 1865)

Maxwell combined the laws of electricity and magnetism into a set of equations and found that they predicted waves travelling at the speed of light. He concluded that light itself is an electromagnetic wave. His equations underpin radio, radar, mobile phones and all modern electrical engineering.

38. The laws of inheritance (Gregor Mendel, 1865–1866)

Breeding thousands of pea plants, Mendel found that traits are passed on as separate units, now called genes, in predictable ratios. His work was largely overlooked until it was rediscovered in 1900, when it became the foundation of genetics.

39. The periodic table (Dmitri Mendeleev, 1869)

Mendeleev arranged the known elements by atomic weight and grouped those with similar properties. He left gaps for elements not yet discovered and predicted their properties. When gallium, scandium and germanium were found and matched his predictions, the periodic table became chemistry's central organising tool.

40. Nucleic acid (Friedrich Miescher, 1869)

Studying white blood cells from pus on surgical bandages, Miescher isolated a phosphorus-rich substance from cell nuclei that he called "nuclein". It was what we now call DNA. Its role as the carrier of genetic information was not proven for another 75 years.

41. Radio waves (Heinrich Hertz, 1887–1888)

Hertz generated and detected electromagnetic waves in his laboratory, showing they travel at the speed of light and can be reflected and focused like light. He confirmed Maxwell's predictions, and within a decade others had used the waves for wireless telegraphy. The unit of frequency, the hertz, is named after him.

42. The neuron doctrine (Santiago Ramón y Cajal, late 1880s)

Using a staining method developed by Camillo Golgi, Cajal showed that the nervous system is made of separate cells, neurons, that communicate across tiny gaps rather than a continuous network. The two shared the 1906 Nobel Prize in Physiology or Medicine, and Cajal's drawings are still used to teach neuroscience.

43. Viruses (Dmitri Ivanovsky, 1892, and Martinus Beijerinck, 1898)

Investigating a disease of tobacco plants, Ivanovsky found that the infectious agent passed through filters that trapped bacteria. Beijerinck showed it multiplied in living plants and called it a virus. A new category of pathogen had been found, responsible for diseases from flu and measles to HIV and COVID-19.

44. X-rays (Wilhelm Röntgen, 1895)

Experimenting with electrical discharge tubes, Röntgen noticed a nearby screen glowing and found a penetrating radiation that could photograph the bones inside his wife's hand. Within months X-rays were being used in hospitals. Röntgen received the first Nobel Prize in Physics in 1901 (Nobel Prize).

45. Radioactivity (Henri Becquerel, 1896, and Marie and Pierre Curie, 1898)

Becquerel found that uranium salts emitted radiation without any external energy source. Marie and Pierre Curie showed this was a property of atoms, coined the term radioactivity and discovered two new elements, polonium and radium. Radioactivity revealed that atoms have an inner structure and led to radiotherapy, radiometric dating and nuclear power.

46. The electron (J. J. Thomson, 1897)

Thomson showed that cathode rays are made of particles much smaller than the lightest atom, carrying negative charge. The electron was the first subatomic particle discovered. Electronics, from radios to computer chips, is the engineering of electrons.

47. Mosquitoes transmit malaria (Ronald Ross, 1897)

Ross found malaria parasites in the stomach of mosquitoes that had fed on an infected patient and later traced the parasite's full life cycle in birds. He received the 1902 Nobel Prize in Physiology or Medicine. Knowing how malaria spreads made mosquito control, bed nets and drainage central to fighting the disease.

The new physics and the new biology (1900–1945)

Quantum theory and relativity rewrote physics, while biologists found genes, hormones, vitamins and antibiotics (Nobel Prize).

48. Energy comes in quanta (Max Planck, 1900)

To explain the colours of light given off by hot objects, Planck proposed that energy is emitted in tiny packets, or quanta. He saw it as a mathematical trick, but it was the beginning of quantum physics, which now explains atoms, chemical bonds, lasers and semiconductors.

49. Blood groups (Karl Landsteiner, 1901)

Landsteiner found that mixing blood from different people sometimes made red cells clump together, and identified the A, B and O groups (AB followed shortly after). Matching donors and recipients made blood transfusions safe, which now saves millions of lives a year. He received the Nobel Prize in 1930.

50. Hormones (William Bayliss and Ernest Starling, 1902)

Bayliss and Starling found that a substance released by the small intestine, which they called secretin, travels in the blood and triggers the pancreas to release digestive juices. Starling coined the word "hormone" in 1905. Endocrinology, the study of chemical messengers, grew from this work.

51. Relativity and the photon (Albert Einstein, 1905)

In one year Einstein explained the photoelectric effect by treating light as particles (photons), showed that space and time depend on the observer's motion, and derived E=mc2E = mc^2. Special relativity is essential for particle accelerators and, together with general relativity, for the accuracy of GPS.

52. Atoms are real (Jean Perrin, 1908)

Many scientists still doubted that atoms physically existed. Einstein had predicted how tiny particles in a liquid would jiggle when struck by invisible molecules, and Perrin's careful measurements of this Brownian motion matched the prediction and gave a value for the number of molecules in a mole. He received the 1926 Nobel Prize in Physics.

53. Making ammonia from air (Fritz Haber, 1909)

Haber found a way to combine nitrogen from the air with hydrogen to make ammonia, and Carl Bosch scaled the process up for industry. Ammonia-based fertilisers from the Haber–Bosch process are estimated to support food production for roughly half of the world's population. The same process was also used to make explosives, a reminder that discoveries can be used for harm as well as good.

54. The atomic nucleus (Ernest Rutherford, 1911)

When Hans Geiger and Ernest Marsden fired alpha particles at thin gold foil, a few bounced almost straight back. Rutherford concluded that an atom's positive charge and nearly all its mass are packed into a tiny central nucleus. The modern picture of the atom begins here.

55. Genes are on chromosomes (Thomas Hunt Morgan, 1910–1915)

Breeding fruit flies, Morgan found that a white-eye mutation was inherited along with the sex chromosomes, and his group went on to map genes along chromosomes. This connected Mendel's units of inheritance to physical structures in the cell. He received the 1933 Nobel Prize.

56. Vitamins (Eijkman, Hopkins and Funk, 1897–1912)

Christiaan Eijkman found that a diet of polished rice caused a beriberi-like disease in chickens, and Frederick Gowland Hopkins showed that animals need small amounts of "accessory food factors" to grow. Casimir Funk coined the word "vitamine" in 1912. Understanding vitamins led to the prevention of scurvy, rickets, beriberi and pellagra.

57. Measuring distances to stars (Henrietta Swan Leavitt, 1912)

Studying photographic plates at Harvard, Leavitt found that Cepheid variable stars that are intrinsically brighter pulse more slowly. By timing a Cepheid's pulse, astronomers could work out its true brightness and therefore its distance. This "standard candle" later let Hubble measure the distances to other galaxies.

58. Continental drift (Alfred Wegener, 1912–1915)

Wegener argued that the continents had once been joined and had drifted apart, pointing to matching coastlines, fossils and rocks on opposite sides of oceans. He could not explain what moved them, and the idea was widely rejected until the discovery of seafloor spreading in the 1960s.

59. General relativity (Albert Einstein, 1915)

Einstein described gravity not as a force but as the curving of space and time by mass and energy. In 1919, measurements during a solar eclipse showed starlight bending around the Sun by the amount he predicted. General relativity explains black holes, gravitational lensing and the expansion of the universe, and GPS satellites must correct for it.

60. Insulin (Banting, Best, Collip and Macleod, 1921–1922)

At the University of Toronto, Frederick Banting and Charles Best extracted insulin from the pancreas, James Collip purified it, and in January 1922 it was given to a 14-year-old boy with diabetes. Type 1 diabetes changed from a death sentence to a manageable condition. Banting and John Macleod received the 1923 Nobel Prize.

61. Other galaxies (Edwin Hubble, 1924–1925)

Using Leavitt's Cepheid method, Hubble showed that the Andromeda "nebula" was far too distant to be part of the Milky Way. It was a separate galaxy. The universe suddenly became vastly larger, containing countless galaxies like our own.

62. Stars are made mostly of hydrogen (Cecilia Payne, 1925)

In her doctoral thesis, Payne used the new physics of atoms to analyse stellar spectra and concluded that stars are made overwhelmingly of hydrogen and helium. Leading astronomers at first resisted the result, but it was soon confirmed. It is the basis of our understanding of how stars shine and how the elements were made.

63. Quantum mechanics (Heisenberg, Schrödinger and others, 1925–1927)

Werner Heisenberg, Erwin Schrödinger, Paul Dirac, Max Born and others developed a complete theory of how matter behaves at atomic scales, including the uncertainty principle. Quantum mechanics explains chemical bonding, the periodic table, semiconductors and lasers, and is the basis of most modern technology.

64. The expanding universe (Georges Lemaître, 1927, and Edwin Hubble, 1929)

Lemaître showed that general relativity allowed an expanding universe and noted that galaxies' speeds appeared to increase with distance. Hubble's 1929 measurements made the relationship clear: distant galaxies are moving away from us, faster the further they are. The universe had a history, which led to the Big Bang theory.

65. Penicillin (Alexander Fleming, 1928, then Howard Florey and Ernst Chain, 1940)

Fleming noticed that a mould contaminating a bacterial culture had killed the bacteria around it. Over a decade later, Florey, Chain and their team at Oxford purified penicillin and showed it could cure infections. Mass production during the Second World War began the antibiotic era. The three shared the 1945 Nobel Prize.

66. Antimatter (Paul Dirac, 1928, and Carl Anderson, 1932)

Dirac's equation for the electron predicted a twin particle with the opposite charge. In 1932 Anderson found it in cosmic-ray tracks and called it the positron. Antimatter is now used in hospitals every day, in PET scans.

67. The neutron (James Chadwick, 1932)

Chadwick identified an uncharged particle in the atomic nucleus with almost the same mass as the proton. The neutron explained isotopes and, because it has no charge, could penetrate nuclei easily, which made nuclear fission possible a few years later.

68. Dark matter (Fritz Zwicky, 1933, and Vera Rubin, 1970s)

Zwicky found that galaxies in the Coma Cluster moved too fast to be held together by their visible matter alone. In the 1970s, Vera Rubin and Kent Ford measured that stars in the outer parts of spiral galaxies orbit just as fast as those near the centre. Most matter in the universe appears to be invisible, and identifying it is still one of science's biggest open questions.

69. Earth's solid inner core (Inge Lehmann, 1936)

By studying how earthquake waves pass through Earth, Lehmann found that some were reflected from a boundary deep inside the liquid core. She concluded that Earth has a solid inner core. Seismology became the main way to map Earth's deep interior.

70. Nuclear fission (Hahn, Strassmann, Meitner and Frisch, 1938–1939)

Otto Hahn and Fritz Strassmann found barium among the products of uranium bombarded with neutrons. Lise Meitner and Otto Frisch explained that the uranium nucleus had split in two, releasing enormous energy, and named the process fission. It led to both nuclear power and nuclear weapons.

71. DNA carries genetic information (Avery, MacLeod and McCarty, 1944)

Oswald Avery, Colin MacLeod and Maclyn McCarty showed that DNA, not protein, was the substance that could transform harmless bacteria into disease-causing ones. It was the first strong evidence that genes are made of DNA, setting the stage for the double helix.

The postwar boom (1945–1980)

Molecular biology, plate tectonics and the Big Bang all took shape in a few decades (OpenStax Biology 2e).

72. The transistor (Bardeen, Brattain and Shockley, 1947)

At Bell Labs, John Bardeen and Walter Brattain made the first working transistor, a semiconductor device that can amplify and switch electrical signals, and William Shockley soon designed an improved version. Billions of transistors now sit on a single computer chip. The three shared the 1956 Nobel Prize in Physics.

73. Radiocarbon dating (Willard Libby, 1949)

Libby showed that living things take in a known proportion of radioactive carbon-14, which decays at a steady rate after they die. Measuring what remains reveals the age of organic material up to around 50,000 years old. Archaeology, geology and climate science were transformed. He received the 1960 Nobel Prize in Chemistry.

74. The double helix (Watson, Crick, Franklin and Wilkins, 1953)

James Watson and Francis Crick proposed that DNA is a double helix with paired bases, using X-ray data from Rosalind Franklin, Raymond Gosling and Maurice Wilkins. The structure immediately suggested how DNA copies itself. Watson, Crick and Wilkins received the 1962 Nobel Prize; Franklin had died in 1958, and her essential contribution is now widely recognised.

75. A safe polio vaccine (Jonas Salk, 1955)

A huge field trial involving more than a million children showed Salk's inactivated polio vaccine was safe and effective, and Albert Sabin's oral vaccine followed. Polio, which paralysed hundreds of thousands of children a year, has since been eliminated from most of the world.

76. Rising carbon dioxide (Charles David Keeling, 1958)

Keeling began precise measurements of carbon dioxide at Mauna Loa, Hawaii. Within a few years his record showed a seasonal rhythm and a steady rise. The "Keeling Curve" is now the longest continuous record of atmospheric carbon dioxide and the clearest evidence that human activity is changing the atmosphere (NOAA).

77. Cracking the genetic code (Nirenberg, Khorana, Holley and others, 1961–1966)

In 1961, Marshall Nirenberg and Heinrich Matthaei showed that a chain of the RNA base uracil (UUU) codes for the amino acid phenylalanine. By 1966 all 64 three-letter codons had been decoded. Knowing the code made it possible to read, and later write, genetic instructions. Nirenberg, Har Gobind Khorana and Robert Holley shared the 1968 Nobel Prize.

78. Plate tectonics (Hess, Vine, Matthews and others, 1960s)

Harry Hess proposed that new seafloor forms at mid-ocean ridges and spreads outwards. Fred Vine and Drummond Matthews showed that magnetic stripes on the seafloor recorded reversals of Earth's magnetic field, as spreading predicted. Wegener's continental drift was revived as plate tectonics, which explains earthquakes, volcanoes and mountain building.

79. Afterglow of the Big Bang (Arno Penzias and Robert Wilson, 1965)

Penzias and Wilson could not get rid of a faint microwave hiss in their radio antenna, coming equally from every direction. It turned out to be the cosmic microwave background, light left over from when the universe was about 380,000 years old. It provided strong evidence for the Big Bang and earned them the 1978 Nobel Prize.

80. Pulsars (Jocelyn Bell Burnell, 1967)

As a graduate student, Bell Burnell noticed a strange, regular signal pulsing every 1.3 seconds in her radio telescope data. It came from a rapidly spinning neutron star, an object made of matter denser than an atomic nucleus. Her supervisor Antony Hewish shared the 1974 Nobel Prize; Bell Burnell's role is now widely celebrated.

81. Quarks (SLAC–MIT experiments, 1968)

Firing high-energy electrons at protons at the Stanford Linear Accelerator Center, Jerome Friedman, Henry Kendall and Richard Taylor found that protons contain smaller point-like particles, confirming the quarks proposed by Murray Gell-Mann and George Zweig. They shared the 1990 Nobel Prize. Quarks are a core part of the Standard Model of particle physics.

82. Recombinant DNA (Stanley Cohen and Herbert Boyer, 1973)

Building on work by Paul Berg, Cohen and Boyer cut DNA from one organism and inserted it into bacteria, which copied it. Genetic engineering was born. Within a decade, bacteria were producing human insulin for people with diabetes.

83. CFCs destroy ozone (Mario Molina and F. Sherwood Rowland, 1974)

Molina and Rowland showed that chlorofluorocarbons (CFCs), used in fridges and aerosols, could rise into the stratosphere and destroy the ozone layer that shields life from ultraviolet radiation. In 1985, British Antarctic Survey scientists reported a deep seasonal ozone "hole" over Antarctica. The 1987 Montreal Protocol phased out CFCs, and the ozone layer is now slowly recovering.

84. Life at deep-sea vents (1977)

Scientists diving in the submersible Alvin near the Galápagos Islands found thriving communities of giant tubeworms, clams and crabs around hot springs on the ocean floor. They depend on bacteria that make food from chemicals rather than sunlight. The discovery widened the search for life on other worlds.

85. A third domain of life (Carl Woese and George Fox, 1977)

Comparing ribosomal RNA sequences, Woese and Fox found that some microbes that look like bacteria are as different from bacteria as bacteria are from humans. They called them archaea. Life is now classified into three domains: bacteria, archaea and eukaryotes.

Modern science (1980–present)

Since 1980, discoveries have come from ever larger collaborations, new instruments and, increasingly, computation (Nobel Prize).

86. An asteroid killed the dinosaurs (Luis and Walter Alvarez, 1980)

The Alvarez team found an unusually high level of iridium, rare on Earth but common in asteroids, in a thin layer of rock marking the end of the age of dinosaurs 66 million years ago. In 1991 the 180-kilometre Chicxulub crater in Mexico was identified as the impact site. It showed that sudden catastrophes can reshape life on Earth.

87. Bacteria cause stomach ulcers (Barry Marshall and Robin Warren, 1982)

Doctors believed ulcers were caused by stress and acid. Warren and Marshall showed that the bacterium Helicobacter pylori causes most of them; Marshall even drank a culture to prove it. Ulcers became curable with antibiotics. They received the 2005 Nobel Prize (Nobel Prize).

88. HIV (Françoise Barré-Sinoussi and Luc Montagnier, 1983)

Barré-Sinoussi and Montagnier isolated the virus that causes AIDS. Identifying it led to blood tests, safe blood supplies and antiretroviral drugs that let people with HIV live long lives. They shared the 2008 Nobel Prize.

89. PCR (Kary Mullis, 1983)

Mullis devised the polymerase chain reaction, a way of copying a tiny piece of DNA billions of times in a few hours. PCR made DNA fingerprinting, genetic testing, ancient DNA research and rapid diagnosis of infections, including COVID-19 tests, possible. He received the 1993 Nobel Prize in Chemistry.

90. Planets around other stars (Michel Mayor and Didier Queloz, 1995)

Planets had been found around a pulsar in 1992, but Mayor and Queloz detected the first planet orbiting a Sun-like star, 51 Pegasi b, by the tiny wobble it caused in its star. More than 6,000 exoplanets have now been confirmed (NASA Exoplanet Archive). They shared the 2019 Nobel Prize.

91. The accelerating universe (Perlmutter, Schmidt and Riess, 1998)

Two teams measuring distant exploding stars found that the expansion of the universe is speeding up, not slowing down. Whatever drives this, called dark energy, makes up most of the universe's energy. Saul Perlmutter, Brian Schmidt and Adam Riess shared the 2011 Nobel Prize.

92. The human genome (Human Genome Project, 2001–2003)

An international project published a draft of the human genome in 2001 and declared it essentially complete in 2003. It revealed about 20,000 protein-coding genes, far fewer than expected. A truly gap-free sequence followed in 2022 (NHGRI). Genome sequencing now guides cancer treatment and diagnoses rare diseases.

93. Reprogramming adult cells (Shinya Yamanaka, 2006)

Yamanaka showed that switching on just four genes could turn mature mouse skin cells into stem cells able to become any cell type; human cells followed in 2007. These induced pluripotent stem cells let researchers grow patients' own cells to study diseases and test drugs. He shared the 2012 Nobel Prize with John Gurdon.

94. Neanderthal DNA in modern humans (Svante Pääbo, 2010)

Pääbo's team sequenced the Neanderthal genome and found that many people living today carry a small percentage of Neanderthal DNA. They also identified a previously unknown group of ancient humans, the Denisovans, from a finger bone. Ancient DNA has rewritten the story of human origins. Pääbo received the 2022 Nobel Prize.

95. CRISPR genome editing (Jennifer Doudna and Emmanuelle Charpentier, 2012)

Doudna and Charpentier showed that a bacterial immune system, CRISPR-Cas9, could be programmed to cut DNA at almost any chosen spot. Editing genes became fast and cheap, and in 2023 regulators approved the first CRISPR-based therapy, for sickle cell disease. They received the 2020 Nobel Prize in Chemistry.

96. The Higgs boson (CERN, 2012)

The ATLAS and CMS experiments at CERN's Large Hadron Collider announced a particle matching the Higgs boson predicted in 1964. It confirmed the mechanism that gives fundamental particles their mass and completed the Standard Model (CERN). Peter Higgs and François Englert shared the 2013 Nobel Prize.

97. Gravitational waves (LIGO, 2015)

On 14 September 2015, the LIGO detectors in the United States recorded ripples in space-time from two black holes merging over a billion light years away, a century after Einstein predicted such waves. Gravitational-wave astronomy is now a new way to observe the universe. Rainer Weiss, Barry Barish and Kip Thorne shared the 2017 Nobel Prize (LIGO).

98. A picture of a black hole (Event Horizon Telescope, 2019)

By linking radio telescopes around the world into one Earth-sized instrument, the Event Horizon Telescope collaboration imaged the shadow of the supermassive black hole in the galaxy M87. In 2022 they released an image of Sagittarius A*, the black hole at the centre of the Milky Way (EHT).

99. mRNA vaccines (Katalin Karikó and Drew Weissman, 2005; vaccines 2020)

Karikó and Weissman found that changing one of the building blocks of messenger RNA stopped it from triggering harmful inflammation. This made mRNA usable as a medicine. In 2020, mRNA vaccines against COVID-19 were developed and authorised in under a year. They received the 2023 Nobel Prize (Nobel Prize).

100. Predicting protein structures with AI (AlphaFold, 2020)

A protein's function depends on its 3D shape, which was slow and expensive to determine experimentally. In 2020 DeepMind's AlphaFold predicted structures with accuracy approaching experimental methods, and its database now covers hundreds of millions of proteins. Demis Hassabis and John Jumper shared the 2024 Nobel Prize in Chemistry with David Baker, who designs new proteins (Nobel Prize).

What these discoveries have in common

Looking across the list, a few patterns stand out:

  • Better instruments come first. The telescope, microscope, spectroscope, particle accelerator and DNA sequencer each opened a wave of discoveries.
  • Surprises matter. Penicillin, X-rays, radioactivity, the cosmic microwave background and pulsars were all found by people investigating something else who took an unexpected result seriously.
  • Good ideas are often resisted. Continental drift, handwashing, Payne's hydrogen-rich stars and bacteria causing ulcers were all doubted at first. Evidence won in the end.
  • Science is collaborative, and credit is uneven. Many discoveries involved people, often women, technicians and junior researchers, who received less recognition than they deserved at the time.
  • Discoveries can be used for good or harm. Fission powers cities and destroyed them; the Haber–Bosch process feeds billions and made wartime explosives.

Where to go next

References

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