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What If? Lab What if Earth had no mountains? Mountains push moving air upward so it drops rain and snow on one side, leaving the other side dry. Many rivers begin high in the mountains, and mountains are home to many plants and animals. Imagine flattening them all, and follow what might change.
What If? Lab What if a mountain wore away? Even the tallest mountains are slowly broken apart by ice, rain, plant roots and wind, and the pieces are carried away by rivers and glaciers. Imagine following a mountain as it wears away: its rock might end up as sand on a beach, mud on a farm or new land at a river's mouth, while moving plates push other mountains up.
What If? Lab What if you boiled water on a high mountain? Water does not always boil at 100 °C. Climb a mountain and the air pressure drops, so water boils at a lower temperature. In our model of the atmosphere, water 5 kilometers up boils at about 83 °C, which is why food cooked in boiling water takes longer high up.
What If? Lab What if glaciers melted? Glaciers are huge, slow-moving masses of ice on land. When land ice melts, its water runs into the ocean and raises the sea. In our model, melting every mountain glacier on Earth would lift the sea by about 40 centimeters; scientists' best estimate is a little less, about 32.
What If? Lab What if Earth were much bigger? Astronomers have found many planets bigger than Earth, called super-Earths. A simple calculation shows that an Earth twice as wide, made of the same rock, would pull twice as hard. Such a world might hold on to more air and might not grow such tall mountains.
What If? Lab What if you climbed Mount Everest? The higher you go, the thinner the air gets. In this lab, travel from sea level to 8.8 kilometers, near the top of Mount Everest, using a model of the atmosphere. Watch the air pressure fall to about a third, the temperature drop far below freezing, and water boil at under 70 °C.
What If? Lab What if the continents stopped moving? Earth's outer shell is broken into giant plates that creep along just a few centimeters a year. Where they meet, they build mountains and cause earthquakes and volcanoes. Imagine the plates stopped: rain, ice and wind would keep wearing the land down, but nothing would push new mountains up.
What If? Lab What if snow were black? Clean snow is white because it reflects most of the sunlight that hits it, which helps it stay cold and frozen. Dark things soak up sunlight and warm up. In some mountains, dust blowing onto snow already makes it melt weeks earlier. Imagine snow that was black, and find out why color matters so much.
What If? Lab What if Earth had no deserts? About one third of Earth's land is desert. Deserts form where sinking air dries out the sky or mountains block the rain, and they are home to animals found nowhere else. Their dust even blows across an ocean to feed the Amazon rainforest. Imagine Earth with no deserts and see what would change.
What If? Lab What if tunnels could be dug anywhere? Tunnels carry trains, cars and water through mountains and under rivers. But digging one is hard: the ground can be solid rock or soft mud, and water is always trying to get in. Explore how tunnel builders hold back rock and water, and how giant boring machines dig and line a tunnel as they go.
What If? Lab What if it rained every day? Rain is wonderful: it waters plants and fills rivers. But what if it rained every day? Soil can only soak up so much, so more water would run into rivers. Some rainforests and mountain slopes get rain very often, and life there is built for it. Explore what daily rain would change.