Meteorologist Alfred Wegener suggests that Earth’s continents aren’t fixed in place, but drift around the globe.
Meteorologist Alfred Wegener suggests that Earth’s continents aren’t fixed in place, but drift around the globe.
Geologist Arthur Holmes publishes The Age of the Earth, presenting the first complete geologic timescale and arguing for using radioactive materials as geologic clocks.
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.
Russian physiologist Ivan Pawlow (Pavlov) reports that mice learn to associate an electric bell with dinner after 300 lessons of the bell accompanying food.
Geologist Arthur Holmes proposes that heat from the radioactive decay of elements in the Earth keeps the planet’s interior partially molten.
German psychiatrist Hans Berger reports the first human electroencephalogram, or EEG.
Edwin Hubble (shown) reports that distant galaxies appear to be flying away from us faster than nearby galaxies, crucial evidence that the universe is expanding.
The electron microscope is invented by Max Knoll and Ernst Ruska (shown), allowing for the investigation of a wide range of materials, including biological samples.
Physicist James Chadwick discovers an electrically neutral particle, the neutron, contained within atomic nuclei.
Images from physicist Carl Anderson’s cloud chamber reveal a positively charged particle with a mass equivalent to the electron: a positron.
Karl Jansky’s discovery of a shortwave radio hiss coming from the Milky Way’s heart is widely publicized, marking the beginning of radio astronomy. Jansky is shown here with his rotating radio antenna.
Fritz Zwicky examines galaxies in the Coma cluster and determines that there is unseen mass, what scientists now call “dark matter.”
Harvard researchers Gregory Pincus and E.V. Enzmann grow rabbit eggs cells to maturity in the laboratory for the first time.
Henry Dale reports the discovery of acetylcholine, a chemical released by nerves to command a muscle to move.
The first artificially produced radioactive isotopes are discovered by Frédéric and Irène Joliot-Curie.
Neurosurgeon Wilder Penfield reports on an epilepsy treatment, now known as the “Montreal Procedure,” that destroys areas of the brain where seizures begin.
Scientists use electroencephalography to show that two types of electrical waves, labeled alpha and beta, occur in the brain.
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.
Seismologist Inge Lehmann discovers that Earth has a solid inner core, distinct from its molten outer core.
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.
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.
After creating large amounts of carbon-14 using a cyclotron, or “atom-smasher,” researchers hail the isotope’s potential as a medical tracer. Several years later, scientists propose using carbon-14 to date objects more than 20,000 years old.
Physicists in the United States produce the first controlled, self-sustaining nuclear chain reaction, in a major step toward an atomic bomb.
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.
Details of an epidural nerve block that allows pain-free childbirth without putting women to sleep are reported.
Leo Kanner reports on his studies of a mental illness in 11 children that causes them to largely ignore the people around them, a disease that would come to be called autism.
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.
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.
J. Lawrence Pool is the first to implant electrodes into a woman with Parkinson’s disease.
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.”
Rita Levi-Montalcini identifies chemicals from mouse tumors that stimulate growth in chick embryos — the discovery of nerve growth factor.
The United States tests the first hydrogen bomb, a thermonuclear weapon 1,000 times more powerful than the bomb dropped on Hiroshima.
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.
Physiologists Nathaniel Kleitman and Eugene Aserinsky report the discovery of rapid eye movement during sleep and link it to dreams.
Scientists report that chlorpromazine, developed to treat nausea and vomiting, also helps sedate mental patients.
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.
Scientists detect the neutrino, an electrically neutral subatomic particle released in radioactive decay and other reactions. It had once been thought to be undetectable.
Columbia University researchers Bruce Heezen, Marie Tharp (shown) and Maurice Ewing create the first comprehensive map of an ocean basin, revealing a deep rift right at the center of a long underwater mountain chain cutting through the North Atlantic.
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.
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.
The U.S. Food and Drug Administration approves the first oral contraceptive, soon known simply as “the pill.”
The first cochlear implants, which translate sounds into electrical stimulation, are implanted in deaf patients, in Los Angeles.
Geologist Harry Hess and geophysicist Robert S. Dietz independently argue in 1961 and 1962 that the seafloor is pulling apart at mid-ocean ridges.
Geophysicist J. Tuzo Wilson suggests that volcanic island chains form as plates move over upwellings of magma in the mantle.
Marian Diamond provides early evidence for the brain’s ability to change, or plasticity, later summarizing her findings with the phrase, “Use it or lose it.”
Arno Penzias (left) and Robert Wilson (right) discover the cosmic microwave background radiation, the relic radiation left over from the Big Bang.
Astronomers describe 12 strange celestial objects that appear a bit like stars and a bit like galaxies as quasars, for quasi-stellar radio sources.
Beatrice Mintz creates a mouse with two mothers and two fathers to demonstrate which parent’s genetic contribution ended up in which region of the body.
Norwegian physiologist Terje Lømo observes that connections between nerve cells strengthen with use, a core principle of neuroscience called long-term potentiation.
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.
The great unifying theory of the earth sciences is born with the publication of two separate studies, one by geophysicist W. Jason Morgan in 1967 and the other by geophysicists Dan McKenzie and Robert Parker in 1968.
The first pulsar — stellar objects emitting beams of radiation that look from Earth like pulses — is discovered by Jocelyn Bell Burnell.
The idea that modern birds evolved from dinosaurs takes hold, with new evidence of warm-bloodedness and fossil discoveries such as the small, carnivorous Deinonychus antirrhopus.
Scientists report for the first time test-tube fertilization of human eggs.
Eric Kandel shows how synapses change in response to learning, early work that led to a greater understanding of short- and long-term memory.
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.
The first detailed image of a living brain is taken by a computerized tomography, or CT, scanner in England. Co-inventor of the technology, Godfrey Hounsfield, is shown.
Studies of radio emissions from Cygnus X-1 support claims that it is a black hole, the first detected black hole candidate.
The first Landsat satellite launched (shown), opening the door to continuous monitoring of Earth and its features from above.
Michael E. Phelps and colleagues invent a technique for seeing radioactive tracers in the living brain called positron emission tomography, or PET.
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.
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.
Scientists find that Earth’s ice ages over the last 500,000 years correlate to three different orbital variations — cycles lasting about 23,000 years, 42,000 years (now said to be 41,000) and 100,000 years, confirming a hypothesis proposed decades earlier by astronomer Milutin Milankovitch.
Dives to the seafloor along the Galápagos Rift reveal the first known active hydrothermal vent — and abundant life (including this purple octopus at one vent site).
Louise Brown is the first baby born using in vitro fertilization.
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.
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.
Astronomers detect the first gravitational lens, seeing a single quasar appear as a double image.
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.
Neurologist Stanley Prusiner identified a misfolded protein, calling it a “prion,” as the infectious agent in the degenerative brain disorder Creutzfeldt-Jakob disease.
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.
Walter Jakob Gehring identifies the homeobox, a cluster of genes expressed in early embryonic development that determine how an organism’s body develops.
The first baby is born from frozen eggs in Australia.
Scientists trace the wiring diagram of the nervous system of a C. elegans worm.
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.
An accident at the Chernobyl nuclear power plant in Ukraine killed or sickened dozens of workers and released radioactive material into the environment, requiring the evacuation and resettlement of hundreds of thousands of residents.
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.
The drug fluoxetine, or Prozac, received approval from the U.S. Food and Drug Administration as a treatment for major depression.
Alan Handyside of London’s Hammersmith Hospital is able to check an embryo for genetic defects before implanting it into a mother’s uterus. This testing, known as preimplantation genetic diagnosis or PGD, enables parents carrying a genetic or chromosomal defect to avoid passing it to their children.
Seiji Ogawa and colleagues at Bell Labs invent functional magnetic resonance imaging, or fMRI, a method that reveals blood flow changes in the brain, a proxy for activity.
NASA launches the Hubble Space Telescope (shown), one of the sharpest eyes to ever peer into the cosmos.
Based on just nine minutes of data, the Cosmic Background Explorer, or COBE, reveals that the cosmic microwave background radiation aligns with what is expected from blackbody radiation, good evidence that it is an afterglow of the Big Bang.
A powerful eruption from the Philippines’ Mount Pinatubo (shown) ejects millions of tons of sulfur dioxide into the stratosphere, temporarily cooling the planet.
Neuroscientists discover that a protein can prompt mature nerve cells in adult mice to divide, dispelling the belief that adult mammals’ brain cells cannot reproduce. Whether this happens in human brains is still unclear.
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.
Cosmologists detect temperature fluctuations in the cosmic microwave background, variations that correspond to ripples in the density of matter shortly after the Big Bang, as expected from inflation.
Astronomers report evidence of Massive Compact Halo Objects at the outskirts of the Milky Way. These MACHOs account for some but not all of galactic dark matter.
Astronomers report the most compelling evidence for the existence of a black hole, at the center of galaxy M87, about 50 million light-years from Earth.
The Intergovernmental Panel on Climate Change establishes that there is evidence of a “discernible” human influence on climate.
Dolly the Sheep 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.
Biologists isolate human embryonic stem cells, which have the potential to become nerves, blood or any other tissue.
Astronomers uncover data indicating that the expansion of the universe is picking up speed.
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.
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.
Astronomers put the age range of the universe at between 13 billion and 14 billion years.
Neurologist Helen Mayberg begins work testing deep brain stimulation on people with severe depression, targeting an area called the subcallosal cingulate.
A magnitude 9.1 earthquake off the coast of Indonesia spawned a devastating tsunami that killed over 250,000 people in 14 countries.
An implanted grid of electrodes called BrainGate allows a paralyzed man to check his e-mail and play games with his brain activity alone.
A technique to control genetically engineered nerve cells (shown) in animal brains precisely using laser light, now known as optogenetics, is reported.
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.
By studying an intergalactic collision (which formed the Bullet Cluster, shown), researchers report compelling evidence of dark matter’s presence in space.
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.
North Carolina sediment cores reveal that sea levels began rising precipitously in the late 19th century, a trend attributed to climate change.
After an earthquake and tsunami, reactors at the Fukushima Daiichi Nuclear Power Station lost power and cooling, resulting in partial meltdowns, explosions and releases of radioactive material. Over 100,000 people were evacuated as a result.
Research groups led by Susumu Tonegawa and Mark Mayford independently create false memories in the brains of mice.
A paralyzed woman controls a robotic arm with her mind, enabling her to drink coffee from a bottle.
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.
Precise analyses of ancient Siberian lava provide the smoking gun, convicting ancient volcanic eruptions in the greatest known mass extinction on Earth 252 million years ago.
The first baby with three biological parents is born with DNA from his mother, father and the mitochondria of an egg donor. The birth raises hopes for preventing inheritance of mitochondrial disorders —and triggers fears of “designer babies.”
Scientists for the first time report the detection of cosmic ripples in spacetime, gravitational waves from colliding black holes, thus verifying one of general relativity’s predictions.
Chinese scientist Jiankui He uses CRISPR/Cas9 to create the first gene-edited babies — twin girls — to reduce their risk of contracting HIV. His actions lead to the formation of an international commission on the clinical use of gene editing.
Researchers with the Event Horizon Telescope report the first image of a black hole, capturing the shadow of M87’s monster on its accretion disk.