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ca. 5000 B.C.E. Egyptians develop the balance and a ca. 62 C.E.

standard unit of weight.

ca. 3000 B.C.E. Egyptians develop a standard unit of ca. 50-70


ca. 1450 B.C.E. Egyptians develop the water clock.

ca. 1150 B.C.E. The first geologic map, the Turin papyrus, is made in Egypt to help mine gold deposits. ca. 110-50

ca. 550 B.C.E. Pythagoras, in Greece, studies acoustics, relating the pitch of a tone to the length of the wind instrument or of the string producing it.

ca. 400 B.C.E. Democritus, in Greece, states that all matter is made up of "atoms" and empty space.

ca. 370 B.C.E. Aristotle, in Greece, describes free fall, but incorrectly claims that heavier bodies fall faster than lighter ones.

ca. 350 B.C.E. Aristotle, in Greece, notes the slow rates of geologic processes such as erosion.

ca. 300 B.C.E. Theophrastus, Greek scientist, publishes "On Stones," including one of the first systematic descriptions and classification of minerals, ores, and their behavior under specific tests such as burning.

ca. 270 B.C.E. Ctesibius of Alexandria, Egypt, invents an accurate water clock, in use until the Renaissance.

ca. 260 B.C.E. Archimedes, in Greece, studies floating bodies and states his principle of buoyancy. He also states the law of the lever.

ca. 130 B.C.E. Hipparchus, from Greece, uses trigonometry to measure the sizes and distance to the Sun and Moon, and orbit ca. 1080 of the Moon around Earth.

ca. 60 B.C.E. Lucretius, in Greece, proposes the atomic nature of matter.

ca. 1010

Hero of Alexandria, Egypt, studies air pressure and vacuum. Pliny the Elder publishes Historia Naturalis in 37 volumes. In these works he described many new minerals and ores, and defined the basis of crystallography. In Greece, Ptolemy publishes Almagest, the first complete record of astronomy. This was followed by his Geographia, which discussed the geography of the Greco-Roman world, and Tetrabiblos, a discourse on astrology and natural philosophy.

I Hsing, in China, develops a mechanical clock.

Jabir ibn Hayyan, Persian polymath, publishes on the geology of India, including the recognition that many of the rocks there were initially deposited deep under the seas. Ibn Sina (Avicenna in Latinized form), a Persian polymath, publishes Kitab al-Shifa (the Book of Cure, Healing or Remedy from ignorance), containing some of the early and influential works on Mineralogy and Meteorology, in six chapters: Formation of mountains; The advantages of mountains in the formation of clouds; Sources of water; origin of earthquakes; Formation of minerals; and The diversity of earth's terrain. Many of these contributed to later theories of uniformitarian-ism, the law of superposition, and catastrophism.

Shen Kuo (also known as Mengxi), Chinese polymath, formulates a theory of geomorphology, including deposition, uplift, erosion, and the role of climate change, in studies of the Taihang Mountains of China.

ca. 1100 Abu'L-Fath 'Abd al-Rahman al-

Khazini, in Persia, proposes that gravity acts toward the center of Earth.

ca. 1100 Maimonides (Rabbi Moshe ben

Maimon) publishes The Guide for the Perplexed, including expositions on the Aristotelian geocentric models for the universe, but with a constantly changing universe.

ca. 1200 Jordanus de Nemore, in Germany, studies motion and explains the lever.

ca. 1235 Roger Bacon emphasizes the importance of experimentation.

1276 Roger Bacon, in England, proposes using lenses to correct vision.

1284 Witelo, in Poland, describes reflection and refraction of light.

1300 Rabbi Issac of Akko estimates the age of the universe to be 13.34 billion years old.

1305 Dietrich von Freiberg, in Germany, describes and explains rainbows.

1543 Nicolaus Copernicus publishes De revolutionibus orbium coelestium, recognizing that the Earth is not the center of the universe and that the solar system is heliocentric, with the Sun at the center.

1546 Niccolo Tartaglia, in Italy, studies projectile motion and describes the trajectory of a bullet.

1563 Tycho Brahe publishes his Ephem-eris, tables of predictions of the locations of the stars, planets, and constellations.

1572 Tycho Brahe observes a supernova in the constellation Cassiopeia, changing the views that the heavens were unchanging.

1582 Galileo Galilei, in Italy, describes the motion of a pendulum, noticing that its period is constant and, for small amplitudes, independent of amplitude.

1583-86 Flemish scientist Simon Stevin investigates hydrostatics and free fall.

1590-95 Zacharias Janssen makes the first microscope.

1590-91 Galileo investigates falling bodies and free fall.

1596 Johannes Kepler publishes his work Mysterium Cosmographicum, a geometric model of a geocentric universe.

1600s Galileo develops the principle of inertia.

1600 English scientist William Gilbert studies magnetism and its relation to electricity and describes Earth as a magnet.

1601 Tycho Brahe suddenly dies. Some theories suggest he was murdered by Johannes Kepler, who took over his position and research.

1604 Johannes Kepler publishes observations of supernovas.

1609 Dutch lens maker Hans Lipper-shey invents the telescope. German astronomer Johannes Kepler presents his first and second laws of planetary motion.

1610 Galileo Galilei publishes his observations of several moons of Jupiter and uses this to argue for a sun-centered model for the universe.

1617-21 Johannes Kepler publishes his

Epitome astronomia Copernicanae (Epitome of Copernican astronomy), including the heliocentric model for the universe, the elliptical paths of planets, and all three laws of planetary motion.

1622 Willebrord Snell presents his law of refraction of light.

1636 French mathematician René Descartes advances understanding of rainbows.

1638 Galileo studies motion and friction.

1657 Christian Huygens publishes the first book on probability theory.

1660-62 Robert Boyle studies gases.

1666-1704 Sir Isaac Newton actively studies a wide range of natural phenomena.

1669 Danish anatomist and geologist Nicolaus Steno publishes Prodromus, the first work to show that fossils are the remains of formerly living organisms, as well as proposing the law of stratal superposition.

1705 Edmund Halley predicts the return of the comet named for him.

1714 Gottfreid Leibniz proposes the conservation of energy.

1736 Carl Linnaeus publishes the first of 12 editions of Systema naturae, a book that outlined a system for classification of plants, animals, and minerals.

1736-65 Leonhard Euler studies theoretical mechanics using differential equations.

1738 Daniel Bernoulli investigates the theories of gases and of hydrodynamics.

1743-44 Jean d'Alembert studies energy in

Newtonian mechanics and proposes a theory of fluid dynamics.

1751 American scientist Benjamin Franklin discovers that electricity can produce magnetism.

1754 Joseph Black discovers "fixed air" (carbon dioxide).

1772-88 French mathematician and physicist Joseph Lagrange investigates theoretical mechanics and proposes a new formulation of Newtonian mechanics.

1774 Abraham Gottlob Werner publishes his book "On the External Characters of Minerals" as a guide to identify minerals based on their characteristics. Werner also argued that granites crystallized from ocean waters, leading a school of thought called Neptunism.

1770-90 James Hutton pioneers the concept of uniformitarianism, that the natural processes that formed structures in old rocks are the same as the natural processes operating on Earth at present. This is often summarized as the quote "the present is the key to the past."

1776-84 French mathematician and physicist Pierre Laplace applies mathematical methods to theoretical physics, particularly to mechanics and electricity.

1785 James Hutton publishes his Theory of the Earth, becoming recognized as the father of modern geology. French physicist Charles Augustin de Coulomb proposes his law of electrostatics. French chemist Antoine Laurent Lavoisier develops the law of conservation of mass and names oxygen.

1790 The French Academy of Sciences establishes the metric system of measurement.

1796 British geologist and surveyor William Smith formulates the principle of fossil succession, laying the foundation for the science of stratigraphy.

1797 British physicists Benjamin Thompson and Benjamin Rumford study the heat generated by work. French chemist Joseph Proust develops the law of definite proportions.

1800 Italian physicist Alessandro Volta develops the electric battery.

1800-02 Jean-Baptiste Lamarck elaborates his theory of evolution based on the inheritance of modified traits.

1801 English physicist Thomas Young demonstrates that light is a wave phenomenon.

1802 French chemist Joseph Louis Gay-Lussac develops his gas law relating pressure and temperature.

1802-05 British chemist John Dalton develops his atomic theory.

1808 French scientist Étienne-Louis Malus discovers and investigates polarized light.

1809 English scientist Sir George Cayley publishes his theoretical studies of aerodynamics, laying the foundation for flight.

1811 Italian scientist Amedeo Avogadro describes gases in molecular terms.

1814 German physicist Joseph von Fraunhofer discovers and investigates optical spectra. French physicist Augustin-Jean Fresnel explains light polarization in terms of light's wave nature.

1818 The first national geologic map is produced, as a map of the United Kingdom by William Smith.

1820 Danish physicist Hans Christian 0rsted and French physicist André-Marie Ampère show that an electric current has a magnetic effect.

1821 English physicist Michael Faraday, who was studying electromagnetism, introduces the concept of magnetic field.

1824 French engineer Nicolas-Léonard-

Sadi Carnot publishes his analysis of heat engines, which leads to the laws of thermodynamics.

1827 German physicist Georg Simon Ohm shows the proportionality of electric current and voltage, known as Ohm's law. English botanist Robert Brown discovers the motion of pollen grains suspended in a liquid, called Brown-ian motion.

1830-33 Charles Lyell publishes his work "Principles of Geology," in which he proposes that geological processes are very slow and the Earth is very old, and emphasizes the uniformitarian concepts of James Hutton.

1831 English physicist Michael Faraday discovers electromagnetic induction, that magnetism can produce electricity. American physicist Joseph Henry invents the electric motor.

1831-36 Charles Darwin collects evidence supporting his theory of evolution while traveling around the globe on the H.M.S. Beagle.

1833-60 Adam Sedgwick maps parts of Wales, and proposes divisions of Paleozoic time. He also identifies the origins of many geologic structures, such as folds and faults.

1837 James Dana publishes his "System of Mineralogy."

1840 English physicist James Prescott Joule develops the law of conservation of energy.

1842 Austrian scientist Christian Dop-pler explains the dependence of the observed frequency on the motion of the source or observer, called the Doppler effect.

1847 German scientist Hermann von Helmholtz expresses the conservation of energy in mathematical terms, the first law of thermodynamics.

1848 English scientist Sir William Thomson (Lord Kelvin) describes absolute zero temperature.

1850 German physicist Rudolf Clausius introduces the concept of entropy, which leads to the second law of thermodynamics. French physicist Jean-Bernard-Léon Foucault measures the speed of light in air, and later in water.

1851 Foucault uses a huge pendulum, known as a Foucault pendulum, to demonstrate the rotation of planet Earth.

1853 British geologist Henry Sorby pioneers the use of the polarizing microscope for petrography and publishes models for the origin of slaty cleavage in rocks.

1854 German mathematician Georg Riemann describes the geometry of curved spaces, applied later by modern physicists to relativity and other problems.

1858 Rudolf Virchow states that cells only arise from other cells. Darwin and Alfred Russel Wallace jointly propose the theory of natural selection.

1859 Charles Darwin publishes On the Origin of Species by Means of Natural Selection, or the Preservation of Favored Races in the Struggle for Life. Louis Pasteur disproves the notion of spontaneous generation.

1859 Scottish physicist James Clerk Maxwell develops the kinetic theory of gases, based on a statistical treatment of the gas particles.

1860 The famous debate on evolution by Thomas Henry Huxley and Bishop Samuel Wilberforce takes place at Oxford.

1862 German physicist Gustav Robert

Kirchhoff introduces the concept of a blackbody, later study of which leads to the development of quantum mechanics.

1866 Haeckel coins the term ecology to mean the study of living organisms and their interactions with the environment and states his famous bioge-netic law, that ontogeny recapitulates phylogeny.

1869 Russian physicist Dmitry Mendeleyev develops the periodic table based on atomic mass. American geologist and explorer John Wesley Powell leads a first expedition to the Grand Canyon, providing some of the first geological descriptions of the western United States.

1871 English physicist John William Strutt (Lord Rayleigh) mathematically relates the amount of scattering of light from particles, such as mol ecules, to the wavelength of the light, thus explaining the color of the sky.

1873 Scottish physicist James Clerk Maxwell presents his set of equations, known as Maxwell's equations, which form a theoretical framework for electromagnetism and predict the existence of electromagnetic waves. Dutch physicist Johannes van der Waals modifies the ideal gas equation to take into account weak attractive intermolecular forces, called van der Waals forces.

1875 Austrian geologist Eduard Suess publishes Die Entstehung der Alpen, a milestone paper in understanding the structural geology of the Alps of Europe and in relating his tectonic theories.

1877 English physicist John William Strutt (Lord Rayleigh) publishes his extensive work on acoustics, the science of sound waves. Grove Karl Gilbert publishes a monograph on the Henry Mountains, showing that intrusive plutons can deform host rock.

1879 Austrian physicist Josef Stefan shows experimentally that the rate of energy radiation from a body is proportional to the fourth power of the body's absolute temperature.

1883 Austrian physicist Ludwig Boltzmann explains Stefan's result as a property of blackbodies, known as the Stefan-Boltzmann law. This lays the foundation for the development of quantum mechanics.

1887 German physicist Heinrich Rudolf Hertz observes the photoelectric effect, the emission of electrons from a metal that is irradiated with light, and discovers radio waves. American scientists Albert Abraham Michelson and Edward Williams Morley attempt to measure the motion of Earth in the ether, a proposed medium for the propagation of electromagnetic waves, with a negative result, which leads to the special theory of relativity in the 20th century.

1890 The first monograph of the U.S. Geological Survey is published, by G. K. Gilbert on the origin of glacial Lake Bonneville.

1893 German physicist Wilhelm Wien shows experimentally that the wavelength at which a blackbody radiates at maximal intensity is inversely proportional to the absolute temperature, known as Wien's displacement law.

1895 Scottish geologist Andrew Lawson identifies and names the San Andreas fault and later (in 1908) authors a famous report on the 1906 earthquake. German physicist Wilhelm Conrad Röntgen discovers X-rays.

1896 French physicist Henri Becquerel discovers radioactivity in uranium.

1897 British physicist Sir J. J. Thomson discovers electrons and develops his "plum pudding model" of the atom, where the electrons are imbedded in a positively charged sphere.

1898 French chemist Marie Curie and physicist Pierre Curie isolate radium, which is highly radioactive.

1900 German physicist Max Planck proposes absorption and emission of radiation in discrete amounts, which introduces the quantum concept.

1904 Lord Ernest Rutherford performs the gold foil experiment that demonstrates the existence of the atomic nucleus.

1905 German/Swiss, later American, physicist Albert Einstein publishes his special theory of relativity. To explain the photoelectric effect, Einstein proposes that light consists of photons.

1910-40 Amadeus Grabau publishes a series of 10 books, outlining the stratigraphic and paleontological history of North America, and later China.

1910 Japanese geophysicist Motonori Matuyama recognizes magnetic reversals in Japanese basalts.

1911 Arthur Holmes becomes the first person to use the uranium-lead decay series to date rocks, showing that the Earth is more than a billion years old. Netherlands physicist Heike Kamerlingh Onnes discovers superconductivity. New Zealand-born British physicist Sir Ernest Rutherford discovers the structure of the atom. American physicist Robert A. Mil-

likan uses his "oil drop method" to determine the charge of an electron.

1911-12 Using X-ray methods, British physicists William Henry Bragg and William Lawrence Bragg and German physicist Max von Laue discover the atomic structure of crystals.

1912 Alfred Wegener proposes a theory of continental drift.

1912-35 Victor Goldschmidt authors a series of papers that lay the foundation for modern geochemistry and proposes geochemical models for the composition of the Earth.

1913 Danish physicist Niels Bohr proposes a "planetary model" of the hydrogen atom to explain the hydrogen spectrum, in which the electrons rotate around the nucleus in orbits like planets around the sun. British physicist, Henry Moseley rearranges the periodic table based on atomic number.

1915 Albert Einstein proposes his general theory of relativity.

1916 American physicist Robert Millikan measures the value of the Planck constant, which characterizes all quantum phenomena.

1917 Joseph Grinnell coins the term ecological niche.

1919 English astronomer and physicist Arthur Eddington leads an expedition that measures the bending of starlight passing near the Sun during a total solar eclipse, which confirms the general theory of relativity.

1920 Pentti Eskola defines the concept of metamorphic facies.

1922 soviet mathematician and meteorologist Aleksander Friedmann shows that the general theory of relativity predicts the universe is expanding.

1923 French physicist Louis de Broglie proposes that matter possesses wavelike properties. American physicist Arthur Holly Compton demonstrates, through the Compton effect, that electromagnetic radiation consists of photons.

1925 German physicist Werner Heisenberg invents a matrix formulation of quantum mechanics. American astronomer Edwin Hubble identifies very distant stars outside the Milky Way Galaxy.

1926 Austrian physicist Erwin Schrodinger publishes his formulation of quantum mechanics in the form of the Schrodinger equation.

1927 Werner Heisenberg proposes his uncertainty principle. American physicists Clinton Davisson and Lester Germer show that electrons possess wave-like properties. Leading to the big bang theory, Belgian astronomer Georges Lemaitre states that the universe began its expansion from a tiny, hot state.

1928 British geologist Arthur Holmes proposes that radioactive decay causes thermal convection in Earth's mantle and that this convection causes the continents to drift. British physicist Paul Dirac derives the Dirac equation, which predicts the existence of antiparticles.

1929 American astronomer Edwin Hubble demonstrates that all galaxies are receding from each other, indicating the expansion of the universe. Alexander du Toit begins to publish observations correlating fossils between South America and Africa in support of continental drift.

1931 Ernst Ruska and Max Knoll make the first electron microscope.

1932 Indian-born American astrophysicist Subrahmanyan Chandrasekhar proposes that when a sufficiently massive star reaches the end of its life, it will collapse to a black hole. American physicists Ernest O. Lawrence and M. Stanley Livingston invent the cyclotron, a particle accelerator for investigating nuclei and elementary particles. American physicist Carl D. Anderson discovers the positron, the electron's antiparticle. British physicist James Chadwick discovers the neutron.

1933 Swiss astronomer Fritz Zwicky studies the rotation of galaxies and shows that they must contain more mass than is visible, introducing the idea of dark matter. Georges Lemaitre proposes the theory of the big bang, initially criticized as being too much like creationist accounts, but later endorsed by Albert Einstein.

1934 French physicists Irème Joliot-Curie and Frédéric Joliot-Curie produce the first artificial radioactive isotopes.

1935 Japanese physicist Hideki Yukawa proposes the theory of the nuclear force, binding protons and neutrons into nuclei, which predicts the existence of mesons.

1936 Hans Stille publishes his models for the tectonic pulses of Europe, correlating different events across Europe, Asia, and eventually the globe.

1937 Normal Levi Bowen proposes models of magmatic differentiation by partial melting and by fractional crystallization. American physicists Carl D. Anderson and seth Neddermeyer discover the muon in cosmic rays.

1938 Soviet physicist Pyotr Kapitsa discovers that liquid helium exhibits superfluidity near 0 K. American physicist Hans Bethe explains the source of energy production in stars as nuclear fusion reactions.

1938-39 Austrian physicists Lise Meitner and Otto Frisch explain that the German chemists Otto Hahn and Fritz Strassmann achieved nuclear fission by bombarding uranium with neutrons.

1939 Linus Pauling publishes The Nature of the Chemical Bond and the Structure of Molecules and Crystals: An Introduction to Modern Structural Chemistry.

1941 Milutin Milankovitch publishes his model that changes in the orbital parameters of Earth change the amount of incoming solar radiation, leading to climate cycles on Earth, preserved as Milankovitch cycles in the rock record.

1942 A team led by Italian/American physicist Enrico Fermi produces the first controlled nuclear fission chain reaction. The United States initiates the Manhattan Project to construct a nuclear fission (atomic) bomb.

1943 As part of the Manhattan Project, the Los Alamos laboratory is built in New Mexico, directed by American physicist Robert Oppenheimer.

1945 Erwin Schrödinger publishes What Is Life, a book that inspires many biologists.

1946 American chemist Willard Frank Libby invents the carbon 14-dat-ing technique for determining when living organisms died. The first programmable digital computer, the Electronic Numerical Integrator and Comparator (ENIAC) starts operation.

1947 A team directed by British astronomer Bernard Lovell completes construction of the first radio telescope. British physicist Cecil Frank Powell discovers the pion, predicted by Yukawa in 1935. American physicists John Bardeen, William Shockley, and Walter Brattain invent the transistor, a semiconductor device.

1948 George Gamow publishes a big bang model for the origin of the universe and predicts the presence of cosmic background radiation and the origin of the chemical elements.

1949 German-American physicist Maria Goeppert Mayer and German physicist Hans Jensen model the nucleus of atoms as consisting of shells of protons and neutrons. American geologist Francis Pettijohn publishes his book Sedimentary Rocks, which laid the foundation for modern sedimentology.

1950 Swedish astrophysicist Hannes Alfven reaches an understanding of the physics of plasmas (ionized gases), with relevance to space science and, later, to nuclear fusion. The United States Congress creates the National Science Foundation for the funding of basic research and science education.

1951-52 American physicists Harold Ewen and Edward Mills Purcell observe the 21-cm radio signal from hydrogen atoms in space.

1954 American seismologist Hugo Benioff recognizes that earthquakes beneath island arcs are concentrated in narrow zones and suggests that the arcs are being thrust over sinking oceanic crust, a forerunner to the modern subduction zone model.

1956 American physicists Clyde Cowan, Frederick Reines, F. B. Harrison, H. W. Kruse, and A. D. McGuire discover the electron neutrino.

1956-57 Chinese-American physicist Chien-Shiung Wu experimentally confirms the proposal by the Chinese-American physicists Tsung-Dao Lee and Chen Ning Yang that the weak force might not obey reflection symmetry.

1957 American physicists John Bardeen, Leon Cooper, and Robert schrieffer propose an explanation for superconductivity in terms of conduction by electron pairs. Bayer and General Electric develop polycarbonate plastics.

1958 Japanese physicist Leo Esaki invents the tunnel diode, which exploits quantum tunneling.

1959 Israeli physicist Yakir Aharonov and American physicist David Bohm predict that magnetic fields can affect particles in an observable, nonclas-sical way when the particles do not pass through the field. Austrian molecular biologist Max Perutz determines the structure of hemoglobin.

1960 Robert Dietz and Harry Hess propose the concept of seafloor spreading. The Aharonov-Bohm effect is observed. American physicist Theodore Maiman constructs the first laser from a ruby crystal.

1962 American physicists Leon M. Leder-man, Melvin schwartz, and Jack steinberger discover the muon neutrino. Rachel Carson publishes Silent Spring, a book that stimulates the environmental movement.

1963 Dutch-American astronomer Maarten schmidt discovers the first quasar (QUASi-stellAR radio source), a very distant object that appears similar to a star but radiates more than some galaxies.

1964 American physicists Murray GellMann and George Zweig independently propose the existence of quarks as components of protons, neutrons, and other hadrons.

1965 American physicists Arno Penzias and Robert Wilson discover the cosmic microwave background. Canadian geologist J. Tuzo Wilson publishes "A New Class of Faults and Their Bearing on Continental Drift" in Nature, a paper widely held to be the start of the plate tectonic paradigm. Cambridge Instruments makes the first commercial scanning electron microscope.

1967 American physicists Steven Weinberg and Sheldon Glashow and Pakistani physicist Abdus Salam independently propose unifying the electromagnetic and weak forces to a single, elec-troweak force.

1967-68 British astronomers Jocelyn Bell and Anthony Hewish discover that certain stars, called pulsars, emit periodic radio pulses. American astrophysicist Thomas Gold explains pulsars as rotating neutron stars.

1969 A group of American physicists, including Jerome I. Friedman, Henry Kendall, and Richard E. Taylor, discover experimental evidence for the existence of quarks inside protons.

1970 John Dewey and John Bird apply the concept of plate tectonics to the ancient Appalachian mountain belt.

1970-73 Physicists develop the "standard model" of elementary particles, which includes the strong and electroweak forces.

1972 NASA launches the first Landsat satellite. Preston Cloud proposes models for the evolution of organisms and relationships between life, atmospheric chemistry, and geology for the early Earth.

1972 Stephen Jay Gould and Niles Eldridge propose the theory of punctuated equilibrium as a method for evolutionary events.

1974 English physicist Stephen Hawking proposes that black holes can radiate particles and eventually evaporate. American physicists Burton Richter and Samuel C. C. Ting and their groups independently discover the charm quark.

1974-77 American physicist Martin L. Perl and colleagues discover the tau particle.

1975-77 Polish-American mathematician Benoit B. Mandelbrot introduces the concept of fractals, patterns in systems that are similar to themselves at all scales.

1977 Robert Ballard and his team discover chemosynthetic communities surrounding hydrothermal vents. Carl Woese proposes a third domain of life, Archaea. American physicist Leon Lederman and colleagues discover the bottom quark.

1978 American astronomer Vera Rubin and others conclude from an analysis of the rotation of galaxies that the gravity from the visible stars is insufficient to keep them from flying apart, and they must contain invisible matter, called dark matter.

1979 French physicist Pierre-Gelles de Gennes publishes his work on the theories of polymers and liquid crystals.

1980 American physicist Alan Guth proposes adding inflation—a very brief period of extremely rapid expansion of the universe—to the big bang theory, in order to better explain observations.

1981 German physicist Gerd Binnig and swiss physicist Heinrich Rohrer invent the scanning tunneling microscope, which can image surfaces to the detail of individual atoms.

1983 A team led by the Italian physicist Carlo Rubbia discovers the W and Z bosons, the carriers of the weak force.

1985 English chemist sir harry Kroto and American chemists Richard smalley and Bob Curl discover the structure of the buckminsterfullerene molecule.

1986 swiss physicist Karl Alexander Muller and German physicist Johannes Georg Bednorz discover high-temperature superconductors, materials that become superconducting at temperatures much farther above 0 K than were previously known.

1989 American astronomers Margaret Geller and John Huchra discover that the galaxies in the universe are located on thin sheets surrounding great voids that are empty of galaxies.

1989-92 The U.S. National Aeronautics and Space Administration (NASA) launches the Cosmic Background Explorer (COBE) satellite, which maps the radiation from the sky in all directions, the cosmic microwave background, a remnant from the big bang. The cosmic microwave background is found to be very uniform and to correspond to the radiation of a blackbody at a temperature of 2.725 K. Tiny angular fluctuations in the radiation's generally uniform distribution are detected, reflecting on some nonuniformity in the universe at a very early age.

1990 NASA launches the Hubble Space

Telescope as a satellite above Earth's atmosphere to study the universe at high resolution.

1993 The u.s. Air Force completes the Global Positioning system (GPs), allowing users on Earth to locate themselves and navigate around the world.

1994 The top quark is discovered at Fermi-lab. Hubble telescope.

1995 American physicists Eric Cornell and Carl Wieman produce a Bose-Ein-stein condensate of 2,000 atoms at a temperature lower than 10-6 K, thus confirming a prediction of Bose-Einstein statistics. American geo-physicists Xiaodong Song and Paul Richards demonstrate that Earth's solid inner core, with a diameter of 1,500 miles (2,400 km), rotates a little faster than the rest of the planet. The top quark is discovered by a group at Fermilab. Anti-hydrogen atoms, consisting of an antiproton and a positron, are created at the European Organization for Nuclear Research (CERN).

1998 Observations of supernovas indicate that the expansion of the universe is accelerating.

2000 A collaboration at Fermilab announces the detection of the tau neutrino.

2001 The first complete Archean ophiolite is discovered in China by American geologist T. Kusky and Chinese geologist J. H. Li.

2003 The Human Genome project, a collaborative group of scientists from many nations, complete the sequence of the human genome.

2006 President George W. Bush announces the Advanced Energy Initiative (AEI) to increase research on technology to reduce oil use for transportation, including hybrid-vehicle batteries, ethanol, and hydrogen-fuel cell vehicles and fueling stations. AEI also supports research into electricity pro duction from clean coal, wind, and solar power.

2008 The U.S. Senate introduces The Green Chemistry Research and Development Act of 2008 for the advancement of research into environmentally friendly chemicals by the National Science Foundation (NSF), National Institute of Standards and Technology (NIST), Environmental Protection Agency (EPA), and Department of Energy.

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