Seismologist Richard Oldham determines that earthquake waves move through the central part of the Earth much slower than through the mantle around it. He surmises that the Earth has a core composed of liquid.
Earth's Inner Core (1930s) In 1936, Inge Lehmann documents that some seismic waves from deep inside the Earth's core do not pass through, but are reflected back. It becomes clear that the Earth has an inner core consisting of a small, solid iron sphere that is surrounded by a thick outer core composed of liquid iron.
Alfred Wegener proposes that all the continents in the world once formed a single, giant landmass that was eventually split apart in a process called "continental drift." Wegener's evidence consists of the "fit" of South America with Africa, fossil distribution and geological similarities.
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Galileo Galilei overturns nearly 2,000 years of Aristotelian belief that heavier bodies fall faster than lighter ones by proving that all bodies fall at the same rate.
Isaac Newton comes to the conclusion that all objects in the universe, from apples to planets, exert gravitational attraction on each other.
Isaac Newton changes our understanding of the universe by formulating three laws to describe the movement of objects. 1) An object in motion remains in motion unless an external force is applied to it. 2) The relationship between an object's mass (m), its acceleration (a) and the applied force (F) is F = ma. 3) For every action there is an equal and opposite reaction.
Microscope lens grinder Anton Van Leeuwenhoek accidentally discovers microorganisms in a drop of water. Using his own microscopes, he observes sperm, bacteria and red blood cells. His observations lay the foundation for the sciences of bacteriology and microbiology.
While studying an orchid, botanist Robert Brown identifies a structure within the cells that he terms the "nucleus."
Carl Woese discovers bacteria are not the only simple-celled prokaryotes (unicellular organisms without a nucleus) on Earth. Many of the organisms classified in the new kingdom of Archaea are extremophiles. Some live at very high or low temperatures, others in highly saline, acidic or alkaline water. Some have been found in environments like marshland, sewage and soil. Archaea are usually harmless to other organisms and none are known to cause disease.
Andreas Vesalius dissects human corpses, revealing detailed information about human anatomy and correcting earlier views. Vesalius believes that understanding anatomy is crucial to performing surgery, so he dissects human corpses himself (unusual for the time).
His anatomical charts detailing the blood and nervous systems, produced as a reference aid for his students, are copied so often that he is forced to publish them to protect their accuracy. In 1543 he publishes De Humani Corporis Fabrica, transforming the subject of anatomy.
William Harvey discovers that blood circulates through the body and names the heart as the organ responsible for pumping the blood. His groundbreaking work, Anatomical Essay on the Motion of the Heart and Blood in Animals, published in 1628, lays the groundwork for modern physiology.
Austrian biologist Karl Landsteiner and his group discover four blood groups and develop a system of classification. Knowledge of the different blood types is crucial to performing safe blood transfusions, now a common practice.
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Joseph Priestley discovers oxygen; later, Antoine Lavoisier clarifies the nature of elements. Priestley produces oxygen in experiments and describes its role in combustion and respiration.
Then, by dissolving fixed air in water, he invents carbonated water. Priestley, oblivious to the importance of his discovery, calls the new gas "dephlogisticated air." Lavoisier gives oxygen its name and correctly describes its role in combustion.
A thousand years of observations reveal that there are stars that move in the sky and follow patterns, showing that the Earth is part of a solar system of planets separate from the fixed stars.
The Earth Moves (1543) Nicolaus Copernicus places the sun, not the Earth, at the center of the solar system.
Planetary Orbits Are Elliptical (1605 – 1609) Johannes Kepler devises mathematical laws that successfully and accurately predict the motions of the planets in elliptical orbits
Austrian monk and botanist Gregor Mendel discovers how genetic information is passed down through generations. In experiments performed on pea plants, he notices that characteristics of a plant's offspring, such as height, exhibit recessive and dominant behavior.
Mendel's findings are ridiculed during his lifetime and he dies never knowing that he would come to be known as the "father of genetics
Walter Alvarez postulates that high levels of iridium found in rock core samples around the world provide evidence that an asteroid impact caused the extinction of dinosaurs. Iridium, a common mineral found in asteroids, was discovered in the clay layer at what is known as the K-T boundary. This layer, at 65 million years, lies between the rocks of the Cretaceous and the Tertiary periods and coincides with the mass extinction of dinosaurs.
In 1822, geologist William Buckland uncovers some really big teeth in England. At the time, there is no word to describe his finds. Twenty years later, in 1842, Sir Richard Owen comes up with the word "dinosaur" to describe several spectacular creatures whose fossils are discovered across England. Megalosaurus is the first dinosaur ever named.
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