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Earth's magnetic field
William Gilbert discovered the Earth's magnetic field, he proposed that the Earth acts like a big magnet whose field aligns the small magnet used as a compass needle. -
The Scientific Method
René Descartes publishes his Discourse on the Method for Guiding One's Reason and Searching for Truth in the Sciences, the source of the famous quote, "I think, therefore I am." He outlines his rules for understanding the natural world through reason and skepticism, forming the foundation of the scientific method still in use today. -
Law of Gravity
Isaac Newton discovered the relationship between the motion of the Moon and the motion of a body falling freely on Earth. By his dynamical and gravitational theories, he explained Kepler’s laws and established the modern quantitative science of gravitation. Newton assumed the existence of an attractive force between all massive bodies, one that does not require bodily contact and that acts at a distance. -
Microscopic Organisms
The existence of microscopic organisms was discovered during the period 1665-83 by two Fellows of The Royal Society, Robert Hooke, and Antoni van Leeuwenhoek. After a lapse of more than 150 years, microscopy became the backbone of our understanding of the roles of microbes in the causation of infectious diseases and the recycling of chemical elements in the biosphere. -
The speed of light
In ancient times, many scientists believed the speed of light was infinite and could travel any distance instantaneously. Danish astronomer Ole Roemer became the first person to prove that light travels at a finite speed. He studied Jupiter’s moons and noted that their eclipses took place sooner than predicted when Earth was nearer to Jupiter and happened later when Earth was farther away from Jupiter. Roemer reasoned this was the result of light moving at a finite speed. -
Global Warming
A number of scientists see evidence of a warming trend on the Earth's surface and attribute it to a rise in the concentration of "greenhouse gases." Global warming theory states that an increase in the average temperature of Earth's atmosphere and oceans since the late 19th century can be attributed to humans and increased emissions of carbon dioxide. According to the theory, temperatures will increase further if emissions of these greenhouse gases continue. -
Magnetic Field Reversal
Bernard Brunhes discovers that the Earth's magnetic field has changed direction and reversed itself. His paleomagnetic study of clay baked by a Miocene lava flow 13 million years ago provides the evidence. It is nearly 50 years before his discovery is accepted by the scientific community. -
Continental Drift
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. -
The Big Bang
A Belgian priest named Georges Lemaître first suggested the big bang theory, when he theorized that the universe began from a single primordial atom. The idea received major boosts from Edwin Hubble's observations that galaxies are speeding away from us in all directions. -
Periodic Ice Ages
Serbian astrophysicist Miultin Milankovitch develops a theory relating Earth's motion to long-term climate change and ice ages. His mathematical theory of climate uses variations in solar radiation based on season and latitude. His theory posits that cyclical variations in Earth-sun geometry, such as orbit shape and axis angle, resulting in different levels of solar energy reaching the Earth. -
Seafloor Spreading
Adding his own data on changes in seafloor depth and geology to discoveries of his peers, Harry Hess proposes that Wegener's theory of continental drift is a result of seafloor spreading. He hypothesizes that molten magma from beneath the Earth's crust is oozing up between the plates in the Great Global Rift (now referred to as the Mid-Ocean Ridge). As the hot magma cools, it expands and pushes the plates out from the rift, causing the Atlantic Ocean to get wider over time. -
Plate Tectonics
The work of many scientists reveals that the Earth's surface is broken into several interconnected plates of rock. Earth's outermost layer, the lithosphere, is broken into at least seven large, rigid pieces. These plates are moving in different directions and at different speeds (about 1 to 4 inches per year) and are crashing together, pulling apart, and sideswiping each other. All the action at plate boundaries produces phenomena such as mountains, volcanoes, and earthquakes. -
Men Land on the Moon
American astronauts Neil Armstrong (1930-2012) and Edwin "Buzz" Aldrin (1930-) became the first humans ever to land on the moon. About six-and-a-half hours later, Armstrong became the first person to walk on the moon. -
Curiosity Rover
The Curiosity rover landed on Mars, where it has made several significant discoveries, including new evidence of past water on the red planet, the presence of organic molecules that could be related to life, and mysterious seasonal cycles of methane and oxygen that hint at a dynamic world beneath the surface. -
Water on Mars
The European Space Agency announced that ground-penetrating radar data from the Mars Express spacecraft provided strong evidence that a liquid reservoir of water exists underground near the Martian south pole.