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The , named for the antiquities dealer who bought it, is a medical text from ancient Egypt written around 1600 B.C. It contains the oldest description of surgical techniques and scientific writings. Translations show that the writers had a detailed understanding of anatomy and physiology.

The first recorded mention of the idea that Earth orbits the sun comes from ancient India. Written around 1500 B.C., Vedic hymns reference a . About a thousand years later, Greek astronomer introduced this idea to the West, though it failed to take hold. And about a thousand years after that, published his theory concerning the heliocentric model in the 16th century, and he is often credited with this discovery.

Anaximander, a Greek scholar who lived between 610 B.C. 546 B.C., was the first to propose the . He reasoned that human infants need too much nursing and support from mothers, and would never have survived on their own on early Earth. Instead, he proposed that other, self-supporting animals came to be first, and humans must have come from those ancestors.

The Greek physician, , was one of the first to suggest that the brain is the seat of human thought. Before that, people believed the heart controlled thought.

lived in what is now southern Iraq, and was one of the earliest scientists, learning about the world through observations and experiments. He published the "Book of Optics," in which he outlined laws of refraction and the correct model of vision, showing that the eyes see because objects reflect light rays. Previously, in the second century, the Egyptian astronomer and mathematician, , suggested that the eyes radiate light rays.

In 1088, Shen Kuo, Chinese astronomer and government official, published a series of essays documenting his discovery of . The magnetized needle of a compass doesn't point directly north. Instead, because of the generated by the Earth's swirling, metal core, it points either slightly east or west of north, depending on the field’s position at the time. to determine this declination, or the difference between magnetic north and true north, which laid the foundation for the study of geomagnetism.

The first recorded mention of optical lenses came from English philosopher Roger Bacon. While this is the first recorded mention, historians know that people in both Europe and China were already using reading glasses by then. These first lenses eventually led to the and further advances in optics.

In 1609, Italian astronomer became the first to see the moon for what it is: an imperfect, unevenly pitted rock. Most people believed that the moon was a perfect sphere, and challenged the idea that God created the heavens to be perfect. This was just one of Galileo’s astronomical discoveries that angered the Catholic Church.

Before the discovery of circulation, people believed a 1,400-year-old theory proposed by : the liver constantly produced blood, which then traveled to the bodily tissues before the body consumed it all. English physician was skeptical, and after conducting experiments—including collecting data from blood draws and animal and human dissections—he showed that Galen's theories were impossible. Harvey observed beating hearts in animals and calculated the volume of blood that moves through the body every hour, showing that the body could not replenish this much blood regularly, as Galen proposed.

Robert Boyle, an Oxford University chemist, was the first to define chemical elements and their properties. He observed that while most substances can break down into simpler components, a , like hydrogen, can't be broken down further. This definition is still taught in chemistry classrooms today.

After studying centuries of in 1666, the English physicist Sir Isaac Newton devised the law of , the force of attraction between objects that have mass. Gravity is the reason that the Earth attracts people to its surface, and it is the force that keeps Earth in orbit around the sun. Newton's law has since allowed engineers to design spacecraft that overcome Earth's gravitational pull and explore the solar system.

The Montgolfier brothers, not the Wright brothers, are responsible for the . The brothers invented the , and from Annonay, France, they sent up a manned flight in 1783.

In the centuries before vaccines, to , in a process called variolation, people would scratch material from smallpox sores of affected individuals into the arms of those who had never had the disease; sometimes, they would inhale the diseased matter. Afterward, those people would typically develop symptoms of smallpox, but this resulted in fewer deaths than when people contracted the disease by other means. In 1796, English doctor Edward Jenner observed that milkmaids who had had cowpox didn't show any smallpox symptoms after variolation. Later, he tested this idea by a boy with cowpox and exposing him to smallpox, and the boy never showed symptoms.

The was invented in 1809 by German scientist Samuel Thomas von Sömmerring and could transmit a message just 2,000 feet away. It was technically an . Electrodes in the water on the sender's end produced a signal at the receiving end via electrolysis, a process using an electric current to separate a substance like water into its component parts. The amount of gas produced at the receiving end encoded the message. Von Sömmerring's invention predated more sophisticated telegraphs like system that sent a message from Washington D.C. to Baltimore via a telegraph line.

In 1811, 12-year-old Mary Anning made one of her most famous discoveries while exploring the coast of her hometown, Lyme Regis, in southwest England: the fossil. In 1823, she logged another major find, the first complete skeleton of another extinct marine reptile, the . These fossil discoveries provided support for the idea of extinction during a time when people believed that life on Earth had existed as is since the planet's creation.

Michael Faraday developed the in 1831. An English chemist, Faraday showed that by moving a magnet back and forth through a coil of wire, he could excite electrons on the wire with the changing magnetic field and generate an .

In 1849, graduated from Geneva Medical College in New York, becoming the first woman in the U.S. to earn a medical degree. Instead of breaking down barriers for women in medicine, the immediate aftermath of her success introduced more obstacles. Geneva Medical College , and Blackwell's sister faced opposition to entering the field because of Blackwell's success.

Throughout her career, Blackwell promoted preventative medicine and physical hygiene, and in 1874, she established the .

At the (a meeting that still occurs today) in Albany, New York, Eunice Foote presented her paper, Foote conducted several experiments in which she filled evacuated glass jars with water vapor, carbon dioxide, or air and then observed how they heated up in the sun. She saw that the jar containing carbon dioxide heated most and further predicted that concentrations of carbon dioxide in the atmosphere might influence the world's temperatures. The male scientist and inventor, , often gets credit for this discovery, but he did not describe the greenhouse effect until a few years later.

British naturalists Alfred Russel Wallace and Charles Darwin codiscovered the theory of evolution. While Darwin was observing and collecting species in the Galapagos islands, Wallace was in modern-day Indonesia, doing the same thing. Wallace realized that animals must adapt to their environment to survive—and so did Darwin—and the two coauthored an 1858 paper arguing that .

1865 marks Austrian monk Gregor Mendel's . Humans have been selectively breeding plants and animals for thousands of years. But to methodically test inheritance patterns of traits and use mathematical models to predict inheritance. Mendel's work also provided the foundation for the study of genetics.

In 1869, Swiss chemist Friedrich Miescher was studying human white blood cells when he identified "," which would come to be known as DNA, within the cells. The importance of this new substance, however, was not fully realized until 1952, when scientists conducted experiments with viruses and bacteria to confirm that .

A feat made possible by the development of the electric telegraph, German scientist Heinrich Hertz proved the existence of electromagnetic waves and transmitted and received the in 1885. This work eventually led to the development of .

In 1903, Marie Curie became the . She received two Nobel Prizes in total: one in physics (1903) and one in chemistry (1911). Throughout her career at the Sorbonne and the University of Paris, , discovered new chemical elements, and worked to develop medical applications for radioactive substances.

require nitrogen to conduct , and farmers often treat crops with nitrogen-containing fertilizers. By the beginning of the 20th century, farmers around the world were using natural sources of their crops, like livestock manure. But without , food production could never have scaled to what supports humanity today. In 1909, German scientists Fritz Haber and Carl Bosch contrived the Haber-Bosch process that allowed large-scale synthetic fertilizer production.

In the Harvard observatory spent her days analyzing the brightness of stars on photographic plates, but because of her sex, she was not allowed to engage in the thoughtful, theoretical astronomy she wanted to do. However, her careful observations led her to change the course of astronomy. She noticed a relationship between the time it took a to go from bright to dim in appearance and its actual brightness. Her discovery allowed astronomers to estimate the distance of stars from Earth more precisely and enabled (for whom NASA's Hubble Space Telescope is named) to determine that other galaxies existed.

Paul Ehrlich was working as a physician in Germany in 1904 when he learned that certain dyes could stain specific bacteria, and decided to search for a drug that operated similarly, selectively killing bacteria. Ehrlich focused on the bacterium that causes and developed and tested hundreds of drugs on syphilis-infected rabbits. By 1909, he had discovered the . His experiments showed that the chemical arsphenamine could treat syphilis.

German researcher Alfred Wegener was one of the first people to propose that Earth's surface wasn't fixed in place. In 1915, he published his theory of . Most rejected this idea, and some components of were incorrect, but over the next few decades, geological discoveries convinced scientists that Earth's crust is made of large, slow-moving plates, a theory called plate tectonics.

British scientists John D. Cockcroft and Ernest T.S. Walton were the first to . They used a particle accelerator to bombard a lithium atom with protons, splitting it in two. In doing so, they confirmed , E=mc², which states that the energy of a particle equals the mass of a still object multiplied by the speed of light, squared. This experiment also had more destructive consequences and contributed to the development of nuclear weapons.

A great deal of science happens near or above the Earth's surface, but scientists also want to know what happens underneath. Before the end of the 19th century, most scientists thought below ground, all the way through. But after the , scientists could observe the movements on Earth's surface generated by disturbances beneath the ground. In 1936, female Danish seismologist Inge Lehmann proposed the Earth had a .

In 1938, , the process of splitting an atom into lighter atoms, was first achieved by the German physicists . They bombarded uranium with neutrons, the neutral particles at the center of atoms, and showed that the uranium had decayed into different elements. Though their discovery would be used to develop nuclear weapons, that team did not encourage this. Instead, they advocated for peaceful applications of their science.

At the University of Pennsylvania, began building the in 1942 for the U.S. Military. Three years later, they finished ENIAC, the Electronic Numerical Integrator And Computer. Though it was a massive machine with 6,000 manual switches and could only run one program at a time, ENIAC signaled the beginning of the modern .

The first in a line of animals that would pave the way for human space travel, fruit flies aboard a U.S. rocket were the in 1947. Researchers wanted to see how the at high altitudes would affect the flies. survived their flight to an altitude of 68 miles.

U.K. physicist Narinder Singh Kapany invented the first in 1952. Kapany based his invention on Irish inventor 1870 experiments transmitting light through mirrored pipes. Today, hundreds of thousands of miles of are responsible for fast internet speeds and long-distance calls.

Graduate student Stanley Miller and University of Chicago professor Harold Urey wanted to know on Earth billions of years ago. In 1953, they simulated the —pumping it full of methane, ammonium, and hydrogen—and connected it to another flask filled with water as a stand-in for the ocean. Electrodes then sparked the "atmosphere" flask as lightning might have. After a week, Miller and Urey detected amino acids in their apparatus, showing that in these conditions on a much younger Earth, ingredients necessary for life may have emerged.

That same year, scientists revealed the using X-ray crystallography. Though Francis Crick and James Watson, who worked together at Cambridge University, are traditionally given credit for this discovery, they only determined the structure because they used unpublished work, without consulting her. Franklin, who was at King's College, had been taking and resolving the structure of DNA herself, but her colleague showed these crucial photos—which Franklin had submitted for publication—to Watson and Crick.

In 1958, scientist Charles David Keeling began the longest-running daily measurements of atop Mauna Loa in Hawaii. While observing seasonal fluctuations of , after a few years, it was clear that these concentrations were trending upward. The graph produced by these measurements is now known as the Keeling Curve, and it provides evidence that carbon dioxide accumulates in the atmosphere.

In the heat of the space race between the U.S. and the U.S.S.R., Soviet cosmonaut became the first woman in space in 1963. She was chosen to pilot her spacecraft, , and throughout her career spent over 70 hours in space, flying around the Earth 48 times.

The first version of the internet is over 40 years old. In 1969, the U.S. Department of Defense Advanced Research Projects Agency (ARPA) created a computer network called ARPANET, the , albeit a more limited one. ARPANET only connected mainframes at universities, government buildings, and defense contractor facilities, motivating the development of a faster, more comprehensive mobile network, like the modern internet.

Tu Youyou led Project 523, a Chinese government-funded effort to caused by parasites resistant to the standard treatment. Tu turned to ancient Chinese medical texts and found that around 400 A.D., people used sweet wormwood to treat intermittent fevers, a symptom of malaria; these texts also guided her in isolating the active compound in wormwood without damaging it. In 1971, Tu Youyou and her team discovered the new antimalarial compound, which became a drug that has saved millions of lives. In 2015, Tu Youyou was awarded the for her research. She did not have a research or medical doctoral degree.

In 1974, a team led by paleoanthropologist Donald Johanson was searching for fossils in Hadar, Ethiopia, when they discovered the first fossils comprising a partially complete skeleton. It was the oldest hominin species at the time—roughly 3.18 million years old—and showed that over 3 million years ago, human ancestors walked upright on two legs.

was a mathematician at the Naval Support Facility in Dahlgren, Virginia, from 1956 to 1958. There, starting in the mid-1970s through the 1980s, she used satellite data to create a and develop GPS technology.

Now, the phrase —CRISPR for short—is associated with the , but it refers to a piece of the bacterial immune system that scientists have now harnessed to change DNA. In 1987, scientists at Osaka University in Japan noticed that the E. coli genome had these strange sequences, CRISPR arrays (although the name CRISPR didn't come on the scene until 2002). The scientists did not know the sequences' purpose at the time, but future researchers learned that the arrays helped bacteria recognize and fend off invading viruses.

Neurological conditions and amputations can deprive people of functions they once relied on, like movement control or hearing. (or brain-computer interfaces) aim to restore some of those functions by linking brains and computational devices. and his colleagues experimented with the in 1988. They developed a program that interpreted the brain signals from a participant wearing an electroencephalogram cap (a cap with electrodes that pick up local brain signals). Participants sat in front of a screen and used their thoughts to move the cursor on the screen either up or down toward different targets. Though a simple design, this research spurred the development of more advanced brain-machine interfaces.

Aleksander Wolszczan and Dale Frail , planets outside the solar system, in 1992. Using the , they located two rocky planets orbiting a star in the Virgo constellation. Since this initial discovery, astronomers have found thousands of exoplanets.

The Human Genome Project, an effort funded by the U.S. government involving scientists around the world, did not end up sequencing the entire human genome, but it sequenced . The "first draft" of the human genome was published in 2000, and the , amounting to 99% of the genome, were published in 2003.

In 2010, scientists published the . The dinosaur in question, Anchiornis, was around the size of a chicken and looked like a woodpecker covered in black and gray feathers, with black and white striped wings and a rust-colored crown. The scientists produced this image by using a powerful microscope to analyze pigments from fossilized Anchiornis feathers.

The idea of the Higgs boson came from in the 1960s, to help explain where mass comes from: Higgs proposed that matter exists immersed in what's now called the Higgs field, which is associated with particles called , and as other particles pass through this field, they can gain mass. The 2012 discovery of the came out of a collaboration of thousands of physicists and confirmed the Standard Model of physics. was one of those scientists most involved in the discovery, which marked the third time she helped .

May 9, 2013, marked the reached 400 parts per million (ppm) in human history and the first time on Earth since over 3 million years ago. The last time averages were consistently above 400 ppm was about 16 million years ago. When , concentrations hovered around 317 ppm. While reaching and does not represent an explicit tipping point in climate change, it does represent for humanity and the climate.

Over a billion years ago, , traces of which didn't reach Earth until 2015. The Laser Interferometer Gravitational-Wave Observatory (LIGO) detectors, one in Louisiana and one in Washington state, recorded the traces of that collision in the form of gravitational waves on Sept. 14, 2015. As part of his theory of general relativity, Albert Einstein predicted the existence of , claiming that these waves are ripples in space-time; the 2015 LIGO detection provided evidence for this.

On April 10, 2019, the world saw the first-ever image of a black hole. An international network of hundreds of researchers working on the Event Horizon Telescope team collected the data necessary to see the , 55 million light-years distant. Computer scientist and her team processed the data to produce the image, which shows a halo of dust and gas swirling at the speed of light around the black hole.