Start here · Essential guide
How Weather Works
Learn how uneven heating from the Sun, air pressure, humidity and fronts combine to produce the clouds, wind and rain we experience from day to day.
Earth and Life
Weather and Geology
Atmosphere, storms, rocks and the moving crust of the Earth.
How Hurricanes Form
Find out how warm ocean water, moist air, low wind shear and Earth's rotation come together to turn a cluster of thunderstorms into a tropical cyclone.
How Rocks Are Formed
Learn how igneous, sedimentary and metamorphic rocks form, and how heat, pressure, erosion and time can turn any rock type into another over millions of years.
How Volcanoes Erupt
Understand how rising magma, dissolved gas and rock viscosity decide whether a volcano oozes lava gently or explodes, with a tour of the main eruption styles.
How Weather Forecasts Are Made
See how satellites, balloons and radar feed computer models that simulate the atmosphere, and why forecasts become less certain the further ahead they look.
Ice Ages and What Caused Them
Explore Earth's glacial cycles, from ancient deep freezes to the most recent ice age, and the orbital, carbon dioxide and continental factors scientists link to them.
Plate Tectonics Explained
Learn how Earth's rigid outer shell is split into slowly moving plates, and the fossil, rock and seafloor evidence that turned continental drift into accepted theory.
What Causes Thunder and Lightning
Learn how ice and water droplets in storm clouds separate electric charge, how a lightning flash forms, and why you hear thunder after you see the flash.
Why Earthquakes Happen
Understand how built-up stress on faults is released as seismic waves, how scientists locate quakes, and what magnitude numbers do and do not tell you.
Why the Ocean Is Salty
Find out where sea salt comes from, how rivers, rocks and undersea vents add it, why it builds up, and why some lakes are saltier than the ocean while others are fresh.
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