Earth rising over moon's horizon


Century of Science


from ScienceNews

396 Milestones in
The human blueprint
All Connections

  1. 1900
    1. Rediscovering Mendel

      Gregor Mendel’s experiments on pea plants, conducted in the 1850s and ’60s, are introduced to a wider audience thanks to three botanists independently studying inheritance.

      The human blueprint
    2. Quanta introduced

      German physicist Max Planck deduces that radiation is absorbed or emitted only in discrete packets, calling them “quanta.”

    3. Particles of light

      Albert Einstein proposes that light travels through space in the form of particles, later called photons.

      Quantum reality
    4. Cepheids as cosmic markers

      Henrietta Leavitt discovers that brighter Cepheid variable stars blink slower than dimmer ones, a relationship that gave astronomers a way to measure cosmic distances.

    5. Population genetics is born

      Mathematician G.H. Hardy and physician Wilhelm Weinberg independently derive a formula for the frequency of gene variants in populations. Their work will become a foundation of the science of population genetics.

    6. Synthetic fertilizer

      Fritz Haber demonstrates a method for making ammonia from nitrogen and hydrogen, which was scaled up by Carl Bosch over the next several years. The Haber-Bosch process made ammonia fertilizer widely available, thus helping to boost agricultural yields.

  2. 1910
    1. Morgan with flies

      Caltech Archives, ID: 1.43-5

      Chromosomes and inheritance

      Thomas Hunt Morgan (shown) discovers a white-eyed mutant in his laboratory fruit flies. His continuing work would confirm that genes, the units of heredity, are located on chromosomes.

      The human blueprint
    2. Piltdown Man

      An amateur archaeologist reports finding fossils of a human ancestor near Piltdown, England. Piltdown Man is touted as evidence that a big brain evolved early in human evolution, but the fossils are later exposed as a hoax

    3. Continental drift

      Meteorologist Alfred Wegener suggests that Earth’s continents aren’t fixed in place, but drift around the globe.

    4. Earth’s story

      Geologist Arthur Holmes publishes The Age of the Earth, presenting the first complete geologic timescale and arguing for using radioactive materials as geologic clocks.

      Shaking up Earth
    5. X-ray crystallography

      Physicists Lawrence Bragg and William Henry Bragg demonstrate that X-rays can be used to accurately determine the position of atoms in a crystal. X-ray crystallography would prove essential in the discovery of the structure of DNA and many other biological molecules.
      Connection: New vistas

    6. Bohr model

      Danish physicist Niels Bohr uses quantum theory, the notion that energy comes in discrete packets, to explain the structure of the hydrogen atom.

    7. black and white historical photo of nine nurses, all of whom are Black


      Army accepts Black nurses

      With the 1918 influenza pandemic racing through military training camps, the U.S. Army Nurse Corps began accepting Black nurses two days after World War I ended. Nine of the first group of 18, shown here around 1919, went to Camp Sherman in Ohio.

      Unsung characters
    8. Pandemic flu

      A deadly strain of influenza spreads around the globe, ultimately killing an estimated tens of millions of people. 

      Epidemics and their aftermath
    9. Mass spectrometer

      After inventing the mass spectrograph, now known as the mass spectrometer, British physicist and chemist Francis Aston uses it to discover a large number of isotopes.

  3. 1920
    1. Great Debate

      Harlow Shapley and Heber Curtis publicly debate whether “island universes” – what we now call galaxies – exist outside the Milky Way.

    2. Defining polymers

      German chemist Hermann Staudinger proposes that the linking together of many small molecules can form materials with high molecular weights, such as natural rubber. He later calls them macromolecules.

    3. Kabwe skull pic

      The Natural History Museum/Alamy Stock Photo

      Kabwe skull

      Miners in what’s now Zambia unearth a roughly 300,000-year-old humanlike skull. Known as the Kabwe or Broken Hill skull, it’s the first ancient hominin fossil discovered in Africa.

      The human story
    4. Richardson in a classroom

      Kurt Hutton/Picture Post/Hulton Archive/Getty Images

      Weather forecasting

      British mathematician Lewis Fry Richardson (shown at center) proposes forecasting the weather by piecing together the calculations of tens of thousands of meteorologists working on small parts of the atmosphere.

    5. black and white photo of Sigmund Freud

      Authenticated News/Getty Images

      Mental trio

      Psychoanalyst Sigmund Freud, shown, describes mental life as a series of conflicts between a person’s primitive instincts, or id, and moral conscience, or superego, mediated by the ego’s considerations of what’s socially acceptable.

      The science of us
    6. professional photos of Edgar Allen and Edward A. Doisy

      From left: NLM/NIH (CC BY 2.0); Washington Univ., NLM/NIH

      Estrogen found

      Two scientists at Washington University of St. Louis, Edgar Allen and Edward Doisy, first isolated estrogen in experimental mice and found that it was produced in the ovaries.

      The mystery of reproduction
    7. Vitamin E

      A new “vitamin X” that is key to animal reproduction is reported; the next year it would be formally named vitamin E.

      Materials that made us
    8. Compton effect

      American physicist Arthur Compton reports that X-rays lose energy when they are scattered by charged particles. The “Compton effect” indicates that light has a particle nature.

      Quantum reality
    9. Dart and skull

      Science History Images/Alamy Stock Photo

      Taung Child

      The discovery in South Africa of a 2.8-million-year-old skull with a blend of apelike and humanlike traits hints that the earliest phases of human evolution happened in Africa. Raymond Dart, shown with the fossil, called the Taung Child, places it into a new genus: Australopithecus.

      The human story
    10. Jiving bees

      Karl von Frisch finds that bees report to hive mates where nectar has been found with a jazzy dance.

    11. Waves/particles

      French physicist Louis de Broglie introduces the idea that particles, such as electrons, could exhibit the properties of waves.

      Quantum reality
    12. black and white photo of Cecilia Payne seated at a desk looking at the camera

      Smithsonian Institution/Flickr

      Stellar makeup

      Cecilia Payne (shown) discovers what stars are made of: mostly hydrogen and helium.

    13. Scopes trial

      The largest U.S. science society pledges its support of Tennessee teacher John T. Scopes, who has been arrested for teaching evolution.

    14. Matrix mechanics

      German physicist Werner Heisenberg develops a way to describe the energies of electrons in atoms using matrix algebra. His approach became known as matrix mechanics.

      Quantum reality
    15. Tin Goose

      The Ford Trimotor takes its first flight. The all-metal plane was reliable and comfortable for passengers, and commercial airlines quickly adopted it.

      Materials that made us
    16. Wave mechanics

      Physicist Erwin Schrödinger develops “wave mechanics,” a way to describe the energies of electrons in atoms by viewing electrons as waves. Wave mechanics was soon shown to be mathematically equivalent to the matrix mechanics proposed by Werner Heisenberg the previous year.

      Quantum reality
    17. Quantum probabilities

      German physicist Max Born shows that Erwin Schrödinger’s wave equation can be used to calculate the probabilities for various possible outcomes of an atomic observation but does not allow prediction of a single specific outcome.

      Quantum reality
    18. Peking Man

      Based on a tooth found at China’s Zhoukoudian site, Davidson Black identifies a new hominin species named Sinanthropus pekinensis (now called Homo erectus) that lived several hundred thousand years ago.

      The human story
    19. Ice Age Americans

      The discovery of a flint point alongside the remains of prehistoric buffalo in Folsom, N.M., helps convince anthropologists that humans have lived in the Americas since the Ice Age.

      The human story
    20. Complementarity

      Danish physicist Niels Bohr presents the principle of complementarity, arguing that both particle and wave views are necessary for a full description of the subatomic world.

      Quantum reality
    21. Heisenberg pic

      AIP Emilio Segrè Visual Archives

      Uncertainty principle

      German physicist Werner Heisenberg (shown) deduces that it is impossible to precisely measure both the location and velocity of a subatomic particle at the same time. Heisenberg’s principle is called both revolutionary and disturbing by Science News-Letter in 1929.

      Quantum reality
    22. Culture first

      Anthropologist Margaret Mead’s book Coming of Age in Samoa controversially argues that casual sexuality and other cultural practices on a South Pacific island make adolescence smoother for girls there than girls in Western cultures.

  4. 1930
    1. Mendel meets Darwin

      Ronald Fisher publishes a mathematical analysis of how natural selection can change the distribution of genes in a population, helping to synthesize Mendelian genetics with Darwin’s theory of evolution.

      The human blueprint
    2. Fleming pic

      © IWM TR 1468

      Penicillin discovery

      The discovery of a germ-fighting constituent from mold — penicillin — by Alexander Fleming (shown) launches a renaissance in the control of infectious disease.

    3. Random drift

      Sewall Wright begins to publish work showing that “random drift,” or chance fluctuations in a population’s gene frequencies, could be a significant factor in evolution.

      The human blueprint
    4. Moral kids

      In his book The Moral Judgment of the Child, developmental psychologist Jean Piaget argues that children develop moral ideas in three broad stages largely via interactions with peers.

      The science of us
    5. Imperfect recall

      Pioneering memory researcher Frederic Bartlett publishes experiments showing that what people remember about past events consists of a mix of fact and culturally influenced fill-ins.

      The science of us
    6. Positron found

      Images from physicist Carl Anderson’s cloud chamber reveal a positively charged particle with a mass equivalent to the electron: a positron. This antimatter partner of the electron had been foreshadowed by the work of theoretical physicist Paul Dirac.

    7. Flu virus

      British researchers isolate the virus that causes influenza for the first time, after using human throat washings to infect ferrets.

      Epidemics and their aftermath
    8. historical image of Charles Richter

      New York Public Library/Science Source

      Shaking scale

      The Richter scale is proposed by seismologist Charles Richter (shown) to compare the magnitude of different earthquakes. The more accurate moment magnitude scale is now used for most earthquakes.

      Shaking up Earth
    9. Skeleton and living cat

      Rhoeo/iStock/Getty Images Plus

      Schrödinger’s cat

      In the journal Naturwissenschaften, physicist Erwin Schrödinger coins the term Verschränkung, meaning “entanglement,” and develops his famous thought experiment of a cat that exists in a state of simultaneously being alive and dead.

    10. Inner core

      Seismologist Inge Lehmann discovers that Earth has a solid inner core, distinct from its molten outer core.

    11. pic of Turing

      Science History Images/Alamy Stock Photo

      Turing machine

      Alan Turing (shown) sketches out the theoretical blueprint for a machine able to implement instructions for making any calculation — the principle behind modern computing devices.

    12. Muon found

      A new subatomic particle somewhere between an electron and a proton in mass, later termed the muon, is reported from debris of cosmic ray bombardments.

    13. Robust hominins

      In South Africa, Robert Broom identifies a robust form of hominin, named Paranthropus robustus, that had giant molar teeth and a skull built for heavy chewing. The species, now known to have lived 1.8 million to 1.2 million years ago, is evidence that more than one type of hominin once called the region home.

      The human story
    14. Science History Images/Alamy Stock Photo

      Shaping behaviors

      Psychologist B.F. Skinner, shown, presents evidence indicating that behaviors are strengthened or weakened by their consequences in his first book, The Behavior of Organisms.

      The science of us
    15. Circuit design

      Claude Shannon’s master’s thesis “A Symbolic Analysis of Relay and Switching Circuits,” published in 1938, outlines the foundations for digital circuit design.

      The future of computing
    16. Temperatures up

      Engineer and amateur meteorologist Guy Stewart Callendar links a rise in average temperatures around the globe to the release of carbon dioxide from the burning of fossil fuels.

      Our climate change crisis
    17. Women in nylons

      Arthur Tanner/Fox Photos/Getty Images

      Synthetic silk

      E.I. du Pont de Nemours & Co. prepares to market nylon (waterproofing test shown). The synthetic “silk” fiber was invented by chemist Wallace Hume Carothers.

      Materials that made us
    18. Teflon

      Chemist Roy Plunkett invents the superslick material polytetrafluoroethylene, more commonly known by its trademark Teflon.

      Materials that made us
    19. Science Source

      Nuclear fission

      In a discovery that portends the possibility of atomic bombs, Otto Hahn (right) and Fritz Strassmann report evidence that uranium atoms produce barium when bombarded with neutrons. As explained by their collaborator Lise Meitner (left) and her nephew Otto Frisch, this is fission, the splitting of atoms.

    20. Fluorine for teeth

      Epidemiological data show that adding fluorine to drinking water cuts the risk of cavities.

  5. 1940
    1. Shell model of the nucleus

      Physicists Maria Goeppert Mayer and J. Hans D. Jensen develop a theory of the nucleus as composed of shells of protons and neutrons. It explains why nuclei with certain “magic numbers” of protons and neutrons are more stable.

      Cracking the atom
    2. Chromatography advance

      Archer Martin and Richard Synge report a new form of chromatography called “partition chromatography.” It formed the basis for much of the separation and analysis of complex mixtures today.

    3. Manhattan Project gets into gear

      With the formation of the Manhattan Engineer District, the United States kick-starts a massive project to build an atomic bomb, which employed more than 120,000 people at its peak.

      Cracking the atom
    4. DNA and inheritance

      Oswald Avery, Colin MacLeod and Maclyn McCarty report evidence that DNA is the carrier of genetic information, though the result is not widely accepted at first.

      The human blueprint
    5. National Nuclear Security Administration, Nevada Site Office/U.S. Dept of Energy

      Dropping the bomb

      In July, the United States tests the atomic bomb in the New Mexico desert. In August, the U.S. drops two bombs on Japan, killing more than 100,000 people and hastening the end of World War II.

    6. Chemical mutation

      Experiments in mice show that chemicals can — like radiation — induce mutations.

      The human blueprint
    7. Computing architecture

      John Von Neumann describes a computing architecture that will become the standard for decades to come.

    8. Dynamo theory

      Physicist Walter M. Elsasser and geophysicist Edward Bullard separately propose between 1946 and 1949 that Earth’s magnetic field is a self-sustaining dynamo generated by the movement of fluid in the liquid outer core, which produces an electric current.

      Shaking up Earth
    9. Three transistor guys

      Hulton Archive/Getty Images


      John Bardeen, William Shockley and Walter Brattain (shown from left to right) of Bell Laboratories demonstrate the transistor, which would replace vacuum tubes and pave the way for modern computing.

    10. x-ray of a skull

      J. L. Pool/J. Am. Geriatr. Soc 1954

      Electrodes for Parkinson’s

      J. Lawrence Pool is the first to implant electrodes into a woman with Parkinson’s disease.

      Our brains, our futures
    11. Information theory

      Claude Shannon’s “A Mathematical Theory of Communication” establishes the new field of information theory.

      The future of computing
    12. Neurons firing, wiring

      Canadian psychologist Donald Hebb publishes his account of how neurons reinforce each other’s activity, a description that’s now shorthanded, “fire together, wire together.”

      Our brains, our futures
  6. 1950
    1. McClintock pic

      Smithsonian Institution/Science Service, restored by Adam Cuerden/Wikimedia Commons

      Transposons discovered

      Barbara McClintock (shown) describes her studies from corn kernels of genetic elements that can move from chromosome to chromosome — transposable elements, or transposons.

    2. Milky Way is a spiral

      William W. Morgan and colleagues present a model of the Milky Way’s shape made of cotton balls to the American Astronomical Society meeting, depicting the galaxy as a spiral. The team received a raucous ovation with stomping feet.

      Other worlds
    3. HeLa cells

      Doctors take samples of cervical cancer cells from a Black woman named Henrietta Lacks. The cells, which divide indefinitely, were shared and studied widely without Lacks’ consent, becoming a key tool in biomedical research. 


      Norethindrone made

      Luis Miramontes (shown) made one of the first active ingredients in birth control pills – norethindrone.

      Unsung characters
    5. Cholesterol woes

      Physicians link atherosclerosis to the circulation of large fatty particles in the blood and suggest that a low-cholesterol diet could prevent the condition.

    6. Plastics galore

      Phillips Petroleum chemists J. Paul Hogan and Robert Banks, while studying new ways to make gasoline, discover polypropylene, which also leads to a new way to make high-density polyethylene.

      Materials that made us
    7. The H-bomb drops

      The United States tests the first hydrogen bomb, a thermonuclear weapon 1,000 times more powerful than the bomb dropped on Hiroshima.

      Cracking the atom
    8. More evidence for DNA

      A blender experiment by Alfred Hershey and Martha Chase demonstrates that DNA, not protein, is the genetic material.

      The human blueprint
    9. Grace Hopper



      Grace Hopper (shown) creates the first compiler. It translated instructions into code that a computer could read and execute, making it an important step in the evolution of modern programming languages.

    10. Hidden variables

      Building on earlier work by French physicist Louis de Broglie, theoretical physicist David Bohm suggests a deterministic interpretation of quantum theory that incorporates “hidden variables.”

      Quantum reality
    11. UC San Diego School of Medicine

      Hippocampus and memory

      A patient known as H.M. undergoes surgery to remove his hippocampus, later revealing the role that the brain structure plays in memory. Studies of his postmortem brain (shown) complicated the picture.

      Our brains, our futures
    12. Watson and Crick

      A. Barrington Brown/Science Source

      Double-helix structure of DNA

      James Watson (left) and Francis Crick (right) report in Nature the discovery of the double-helix structure of the DNA molecule. Papers from Rosalind Franklin and Maurice Wilkins, which appear alongside Watson and Crick’s report, provide essential evidence.  

      The human blueprint

      RNA and protein synthesis

      Vincent G. Allfrey, Alfred E. Mirsky and Marie Maynard Daly (shown) report direct experimental evidence that protein synthesis requires RNA.

      Unsung characters
    14. Narinder Singh Kapany

      Joseph McKeown/Picture Post/Hulton Archive/Getty Image

      Fiber optics feat

      Narinder Singh Kapany successfully sent high-quality images through a bundle of optical fibers.

      Unsung characters
    15. Poliovirus plaque assay

      Marguerite Vogt and Renato Dulbecco publish a method for purifying and counting poliovirus particles. Vogt and Dulbecco’s approach remains the gold standard for purifying and counting virus particles.

      Unsung characters
    16. photo of Canyon Diablo meteorite

      Geoffrey Notkin, Aerolite Meteorites of Tucson/Wikimedia Commons (CC BY-SA 2.5)

      Age of Earth

      Geochemist Clair Patterson sets the age of the Earth at 4.550 billion years, relying on ages of meteorites (including the Canyon Diablo meteorite, shown) that formed around the same time.

    17. Neutrino found

      Scientists detect the neutrino, an electrically neutral subatomic particle released in radioactive decay and other reactions. It had once been thought to be undetectable.

      Cracking the atom
    18. AI as a field

      A workshop for a small group of scientists organized by John McCarthy at Dartmouth College is often considered the beginning of the field of artificial intelligence.

      The future of computing
    19. General circulation model

      Meteorologist Norman Phillips develops the world’s first general circulation climate model, which captures how energy flows between the oceans, atmosphere and land.

      Our climate change crisis
    20. Nuclear power

      The first full-scale commercial nuclear power plant, known as Calder Hall, switched on in Cumbria, England.

    21. Steroids made

      Scientists show how living things manufacture steroids, suggesting ways to block cholesterol formation.

    22. a person playing chess

      Jeremy Bishop/Unsplash

      Rational limits

      A decision-making model developed by economist Herbert Simon contends that people use experience-based rules of thumb to work around limited knowledge and time when dealing with complex challenges, such as playing chess.

      The science of us
    23. Parity violation

      Particles that are mirror images — those with opposite “handedness” or orientation of their spin — don’t necessarily behave identically. Chien-Shiung Wu and colleagues report the discovery of this phenomenon, called parity violation, in decays of cobalt-60 atoms.

      Cracking the atom
    24. Carbon dioxide buildup

      Scientists Roger Revelle and Hans Suess report that oceans do not take up as much carbon dioxide as previously thought, which suggests much of the gas produced by human activities is going into the atmosphere.

      Our climate change crisis
    25. Superconducting theory

      John Bardeen, Leon Cooper and Robert Schrieffer set out a theory explaining how electron pairs can flow without resistance through low-temperature materials.

      Materials that made us
    26. Everett

      Photograph by Alan Richards, Courtesy of AIP Emilio Segrè Visual Archives

      Many worlds

      American physicist Hugh Everett III proposes what’s now known as the “many worlds” interpretation of quantum mechanics. An experiment does not create one reality from many quantum possibilities, argues Everett (shown), but instead identifies only one of many branches of reality.

      Quantum reality
    27. Keeling portrait

      SIO Photographic Laboratory records. SAC 0044. Special Collections & Archives, UC San Diego

      Keeling curve

      Geochemist Charles David Keeling (shown in 1988) begins tracking the rise in atmospheric carbon dioxide at Mauna Loa in Hawaii. The record, which continues through today, has become one of the most iconic datasets in all of science.

      Our climate change crisis
    28. Diabetes types

      Henry Dolger reports that diabetes is really two diseases: type 1 with little or no insulin made, and type 2 in which the body doesn’t use insulin well.

    29. Carbon fibers

      Physicist Roger Bacon, working at Union Carbide in Parma, Ohio, demonstrates the first high-performance carbon fibers.

      Materials that made us
    30. Leakey luck begins

      At Olduvai Gorge in Tanzania, Mary Leakey finds the skull of a robust hominin. She and her husband, Louis Leakey, name it Zinjanthropus boisei (now called Paranthropus boisei). The discovery shifts the focus of hominin fieldwork to East Africa.

      The human story
    31. Vision insight

      David Hubel and Torsten Wiesel illuminate the visual system in the cat, opening up an area of inquiry for how brain systems handle information from the senses.

      Our brains, our futures
  7. 1960
    1. Birth control pill

      The U.S. Food and Drug Administration approves the first oral contraceptive, soon known simply as “the pill.”

      The mystery of reproduction
    2. a laboratory device with switches and dials

      Isabelle Adam/Flickr (CC BY-NC-ND 2.0)

      Shocking obedience

      Experimental studies of people’s willingness to follow orders to administer what they think are electric shocks to an unseen stranger gain fame and notoriety for social psychologist Stanley Milgram (Milgram’s “shock box” is shown).

    3. Cracking the code

      Scientists reveal how the sequence of DNA’s four chemical subunits encode the instructions for the creation of the amino acids that make up proteins. One team including Francis Crick and Sydney Brenner discovers that it’s a triplet code, with each sequence of three subunits, or “genetic letters,” coding for one amino acid. In the same year, Marshall Nirenberg and Heinrich Matthaei report the three-letter sequence associated with one particular amino acid, jump-starting efforts to identify more.

      The human blueprint
    4. RNA messengers

      Jacques Monod and François Jacob describe messenger RNA and its role in carrying genetic information from the cell nucleus to the ribosome for protein synthesis.

      The human blueprint
    5. Carson

      USFWS/Flickr (CC BY 2.0)

      Silent Spring

      Rachel Carson (shown) publishes the book Silent Spring, raising alarm over the ecological impacts of the pesticide DDT. The book helps catalyze the modern U.S. environmental movement.

    6. Hot spots

      Geophysicist J. Tuzo Wilson suggests that volcanic island chains form as plates move over upwellings of magma in the mantle.

      Shaking up Earth
    7. Breast cancer screening

      Mammography is shown to be a valuable gauge of the presence of breast tumors.

    8. Handy man

      Louis Leakey and colleagues report that a collection of fossils found at Tanzania’s Olduvai Gorge are the earliest known remains from the genus Homo. The researchers fold the fossils into a new species, Homo habilis, thought to have lived about 2.4 million to 1.4 million years ago. The classification remains controversial.

    9. black and white photo of Arno Penzias (left) and Robert Wilson (right)

      Keystone Press/Alamy Stock Photo

      Background radiation

      Arno Penzias (left) and Robert Wilson (right) discover the cosmic microwave background radiation, the relic radiation left over from the Big Bang.

    10. BASIC unveiled

      Beginner’s All-purpose Symbolic Instruction Code, a computer programming language designed to be easy to use, successfully runs its first programs on a General Electric computer at Dartmouth College.

      The future of computing
    11. Bell test

      Physicist John Bell devises a mathematical theorem that would allow researchers to experimentally rule out any “hidden variables” that might explain the results of quantum entanglement experiments in classical, deterministic terms.

      Quantum reality
    12. Kwolek and molecule

      Hagley Archive/Science Source


      Chemist Stephanie Kwolek (shown) invents Kevlar while looking for light, strong fibers to replace steel wires in car tires.

    13. Strong connections

      Norwegian physiologist Terje Lømo observes that connections between nerve cells strengthen with use, a core principle of neuroscience called long-term potentiation.

      Our brains, our futures
    14. Harry Whittington looking at fossils

      Geological Survey of Canada

      Wonderful life

      Harry Whittington (shown) leads an expedition to Canada’s Burgess Shale, identifying a riot of new and unusual forms of animal life and boosting studies into the Cambrian explosion.

      Shaking up Earth
    15. Human-ape split dated

      By studying blood proteins, Vincent Sarich and Allan Wilson develop a “molecular clock” for primate evolution. The pair estimates that humans and African apes diverged about 5 million years ago. The latest estimates suggest that humans and chimpanzees, now known to be our closest living relative, diverged sometime between 9 million and 6 million years ago.

      The human story
    16. Heart transplant

      Christiaan Barnard in Cape Town, South Africa, transplants a human heart into Louis Washkansky.

    17. Mother of all demos

      American inventor Douglas Engelbart, at a meeting in San Francisco, demonstrates in one system most of the elements of modern personal computing.

      The future of computing
    18. DRAM

      Robert Heath Dennard receives a patent for dynamic random access memory that requires just one transistor, ultimately leading to big boosts in computer memory density.

      The future of computing
    19. Population bomb

      A book by biologists Paul and Anne Ehrlich popularizes the notion of a “population bomb” in which global overpopulation would lead to mass starvation.

      Our climate change crisis
    20. ARPANET

      The ARPANET is born, as two computers — one at UCLA and one at the Stanford Research Institute — link up and share a message.

      The future of computing
    21. Rubella vaccine

      The first rubella vaccine is licensed in the United States, following an epidemic during which 20,000 children were born with congenital rubella syndrome, which can include hearing loss and developmental problems.

      Epidemics and their aftermath
  8. 1970
    1. Earth Day sign

      Archive Photos/Getty Images

      Earth Day

      The first Earth Day, organized by U.S. senator Gaylord Nelson and graduate student Denis Hayes, is celebrated.

      Our climate change crisis
    2. Cell division

      Studying baker’s yeast, geneticist Leland H. Hartwell identifies genes that regulate how cells divide as well as proteins that halt division if a cell’s DNA is damaged.

    3. Restriction enzymes as a tool

      Restriction enzymes, which cut DNA in specific locations, are successfully used for the first time. They would become an essential tool for molecular biology.

    4. Microprocessor

      Federico Faggin, Ted Hoff and Stanley Mazor develop what’s widely considered the first microprocessor, the Intel 4004, a single-chip central processing unit, or CPU, with 2,300 transistors.

      The future of computing
    5. Chipko movement

      A group of women in India lead a series of widely publicized protests against deforestation, linking environmental protection with the protection of human communities.

      Our climate change crisis
    6. Quarks and the November revolution

      Two teams of physicists find a new subatomic particle, the J/psi, which, it soon became clear, could be explained only by a new type of quark, the charm quark. This discovery and others during the period, known as the November revolution, quelled lingering doubts that quarks were real constituents of larger particles such as protons, neutrons and the J/psi.

    7. Lunar origins

      Astronomers William Hartmann and Donald Davis propose in 1975 the Giant Impact Hypothesis, suggesting the moon formed out of material ejected from Earth after a large collision. Space scientist Alastair Cameron and astronomer William Ward developed the same idea independently, proposing it in 1976.

      Shaking up Earth
    8. Kids looking at a computer

      D&P Valenti/ClassicStock/Getty Images

      Personal computers

      Three computers released this year — the Commodore PET, the Apple II and the TRS-80 (an early version shown) — help make personal computing a reality.

      The future of computing
    9. Body planning

      Work reported by Edward Lewis in 1978 and Christiane Nüsslein-Volhard and Eric Wieschaus in 1980 reveals which genes control early embryonic development in fruit flies. The discoveries help explain congenital defects and lead to research on similar genes that determine the human body plan.

    10. black and white photo of Vera Rubin

      AIP Emilio Segrè Visual Archives, Rubin Collection

      Dark matter levels up

      Vera Rubin (shown), Kent Ford and Norbert Thonnard measure the rotation rates of stars in outer parts of galaxies, strongly implying the existence of dark matter.

  9. 1980
    1. Cosmic collision

      Luis Alvarez and Walter Alvarez publish a report saying that a large space rock hitting Earth was responsible for the mass extinction event 66 million years ago that killed off all nonbird dinosaurs. The father-son team proposed the idea at American Geophysical Union’s annual meeting the year before.

      Shaking up Earth
    2. PCR invented

      Kary Mullis invents the polymerase chain reaction technique, which can make millions of copies of a DNA sequence in a short amount of time.

    3. Nuclear winter

      Scientists including Carl Sagan publish a paper titled “Nuclear Winter: Global Consequences of Multiple Nuclear Explosions” that describes how smoke from cities annihilated by nuclear weapons and from forest fires ignited by airbursts could bring on global cooling.

      Our climate change crisis
    4. 3-D printing

      Chuck Hull invents stereolithography, an early 3-D printing technique.

      Materials that made us
    5. photo of Kimeu

      Marion Kaplan/Alamy Stock Photo

      Turkana discovery

      In Kenya, Kamoya Kimeu (shown in 1977) discovers a 40 percent complete skeleton of a Homo erectus youngster nicknamed Turkana Boy. Studies of the fossil suggest that humanlike stature may have evolved by 1.6 million years ago.

      The human story
    6. Alzheimer’s discovery

      George Glenner and Caine Wong discovered a “novel cerebrovascular amyloid protein.” That was amyloid-beta, the key component of plaques in the brains of people with Alzheimer’s disease.

      Our brains, our futures
    7. Quantum cryptography

      Physicist Charles Bennett and computer scientist Gilles Brassard propose a theoretical system for quantum cryptography, which would use photons in a superposition of states to create a secure key.

      Quantum reality
    8. schematic diagram of the nervous system of C. elegans

      J.G. White et al/Proceedings of the Royal Society B 1986

      Worm connectome

      Scientists trace the wiring diagram of the nervous system of a C. elegans worm.

      Our brains, our futures
    9. Walls and voids

      Margaret Geller, John Huchra and Valérie de Lapparent map a section of the observable universe, revealing a structure that encompasses large walls and giant voids.

      General relativity reshaped our universe
    10. African Eve

      A controversial study of modern-day people’s mitochondrial DNA, a type of DNA passed down from mother to child, suggests that all humans can trace their maternal ancestry back to a population that lived in Africa roughly 200,000 years ago.

    11. Great ocean conveyor

      Geochemist Wallace Broecker describes a global system of ocean currents that transports heat and salt between surface and deep waters and around the globe, influencing regional climates. 

    12. Novel antidepressant

      The drug fluoxetine, or Prozac, received approval from the U.S. Food and Drug Administration as a treatment for major depression.

      Our brains, our futures
    13. World Wide Web proposed

      Tim Berners-Lee, a researcher at the European laboratory CERN, writes the first proposal for what would become the World Wide Web.

  10. 1990
    1. Principles of environmental justice

      Delegates at the First National People of Color Environmental Leadership Summit in Washington, D.C., draft and adopt 17 principles of environmental justice, setting a foundation for a growing movement.

      Our climate change crisis
    2. Lithium-ion battery in phone

      Brent Lewin/Bloomberg via Getty Images

      Lithium-ion power

      Sony releases the first commercial lithium-ion battery (a more modern battery is shown), clearing the way for abundant portable electronics.

      Materials that made us
    3. Mirror neurons

      Giacomo Rizzolatti and colleagues discovered a set of neurons in the brains of macaque monkeys that fire both when monkeys do something and see another monkey doing it. These neurons would later be called mirror neurons.

      Our brains, our futures
    4. Rio Earth Summit

      Sue Cunningham Photographic/Alamy Stock Photo

      Rio Earth summit

      World leaders gathered (shown) at the United Nations Conference on Environment and Development in Rio de Janeiro to address how to pursue economic development while also protecting the Earth. The meeting resulted in an international convention on climate change.

      Our climate change crisis
    5. Diagram of qubit

      L. LO


      American physicist Benjamin Schumacher introduces the quantum bit, or qubit.

    6. Quantum teleportation proposed

      Physicist Charles Bennett and collaborators propose that entanglement can, in principle, be used to transfer a particle’s quantum information from one place to another, a feat termed “quantum teleportation.”

    7. Breast cancer genes

      A pair of genes, BRCA1 and BRCA2, appear to play a role in some breast cancers that cluster in families.

      The human blueprint
    8. a sheep

      Getty Images

      First cloned mammal

      Dolly the Sheep (shown) is the first mammal cloned from the DNA of an adult mammal. Ian Wilmut and Keith Campbell of the Roslin Institute transferred the nucleus of an adult mammary gland cell into an egg cell, showing that adult DNA can be reprogrammed to grow a new organism.

    9. Oldest life

      Carbon isotope measurements from Greenland rocks push back the history of life on Earth to 3.85 billion years ago.

    10. Neutrinos have mass

      Physicists discover that neutrinos, long thought to be massless, have a tiny amount of mass. The find raises a slew of still-unanswered questions, whether neutrinos are their own antiparticles, for example, or whether the particles can help explain the scarcity of antimatter in the universe.

      Cracking the atom
    11. photo of Alan Trounson

      Tim Grainger/Monash Univ./Flickr (CC BY-NC-ND 2.0)


      Australian researcher Alan Trounson reports successful vitrification, a method that freezes eggs so rapidly that no crystals can form. The technique boosts the success rate for using frozen eggs in assisted reproduction.

      The mystery of reproduction
  11. 2000
    1. Earliest hominin?

      A nearly complete skull found in Chad and dating to between 7 million and 6 million years ago may be from the earliest known hominin, Michel Brunet and colleagues announce. The team names the find Sahelanthropus tchadensis.

      The human story
    2. SARS outbreak

      A deadly viral pneumonia that emerged in China, called SARS for severe acute respiratory syndrome, sickens more than 8,000 worldwide.

      Epidemics and their aftermath
    3. The hobbit

      A surprising find is reported from the Indonesian island of Flores: A small-brained, short-statured hominin lived there about 100,000 to 50,000 years ago. Named Homo floresiensis, but often called the hobbit, the species may be a case of island dwarfism.

      The human story
    4. Quark-gluon plasma

      Physicists at Brookhaven National Laboratory smash nuclei of gold atoms together to recreate the phase of matter thought to have existed in the early moments of the universe. The quark-gluon plasma is a hot, dense soup of quarks intermingling freely with gluons, which under normal conditions bind quarks into larger particles like protons and neutrons.

      Cracking the atom
    5. Big CO2 emitters

      China passes the United States as the world’s biggest emitter of carbon dioxide, as measured by annual emissions.

      Our climate change crisis
    6. illustration of the Kepler space telescope in space with a starry background


      Kepler up

      The Kepler space telescope (illustrated) found thousands of planets outside our solar system before it stopped operating in 2018.

      Other worlds
  12. 2010
    1. Western blinders

      Cross-cultural researchers led by anthropologist Joseph Henrich review evidence that members of Western, educated, industrialized, rich and democratic (WEIRD) societies are among the least useful populations to study in order to generalize about how resources get shared and other features of human nature.

      The science of us
    2. Tohoku-oki quake

      A magnitude 9.0 earthquake in Japan and the tsunami it spawned kill more than 15,000 people and damaged reactors at the Fukushima power plant, triggering the worst nuclear disaster since Chernobyl in 1986.

      Shaking up Earth
    3. © CERN (CC BY-SA 4.0)

      Higgs is found

      Physicists at CERN near Geneva report discovery of the final particle predicted by the standard model, the Higgs boson. Its existence confirms scientists’ beliefs about how fundamental particles obtain mass.

    4. CRISPR debut

      Jennifer Doudna, Emmanuelle Charpentier and colleagues introduce the CRISPR/Cas9 gene-editing tool. The next year, Feng Zhang and his team would adapt the tool to cut DNA at precise locations in the human genome.

    5. Computer vision

      What’s known as a convolutional neural network makes a big leap in performance in the annual ImageNet Challenge, an object detection and image classification competition. Convolutional neural networks would become the standard architecture for computer vision.

      The future of computing
    6. Microbiome gets attention

      Scientists amass substantial evidence that animals, including people, and their resident bacteria, archaea, fungi and viruses should be thought of as superorganisms.

      The human blueprint
    7. ebola patient and health workers

      KENZO TRIBOUILLARD/AFP via Getty Image

      Ebola outbreak

      An Ebola outbreak in West Africa that began in 2014 and continued through 2016 is the largest to date (health workers assisting a patient in Guinea are shown). The second largest outbreak, in the Democratic Republic of the Congo, begins in 2018 and ends in 2020.

      Epidemics and their aftermath
    8. Sonia Harmand holding fossil

      West Turkana Archaeological Project

      Earliest stone tools

      Archaeologist Sonia Harmand (shown) and colleagues report that flakes, cores and pounding platforms discovered in Kenya are the oldest known stone tools yet found. They are 3.3 million years old, predating the genus Homo by at least half a million years.

      The human story
    9. Homo naledi

      Lee Berger and colleagues report finding a small-brained species of Homo, named Homo naledi, in a South African cave. Although the team thinks H. naledi was an early member of the genus, later dating shows it lived only about 300,000 years ago, making it a contemporary of Homo sapiens.

      The human story
    10. Atmospheric CO2 milestone

      The Keeling curve, an iconic graph that tracks the rise in atmospheric carbon dioxide, passes an annual minimum of 400 parts per million.

      Our climate change crisis
    11. COVID-19 pandemic

      A cluster of pneumonia cases in China with no known cause are reported in December. In 2020 the cases are linked to a novel coronavirus that will soon spread around the globe, killing millions of people and counting.

      Epidemics and their aftermath
  13. 2020
    1. Touching the sun

      NASA’s Parker Solar Probe, launched in 2018, leaves interplanetary space and enters the sun’s atmosphere.