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Planet Earth: fun facts and quiz
The essentials in 7 ideas, with fun facts, an illustrated story and a quiz to see how much you know.
The essentials
Earth’s Layers
Earth has layers: a thin rocky crust, a hot mantle, a liquid outer core and a solid inner core about as hot as the surface of the Sun.
Key fact
It’s about 6,370 km to the centre of the Earth.
Plate Tectonics
Earth’s surface is broken into huge plates that slowly move. Where they meet, we get earthquakes, volcanoes and mountains.
Key fact
Plates move about as fast as your fingernails grow.
The Water Cycle
Water keeps cycling: it evaporates from the sea, forms clouds, falls as rain or snow, and flows back through rivers and the ground.
Key fact
The water you drink has been cycling for billions of years.
Volcanoes
Volcanoes form where molten rock, called magma, reaches the surface. Once it erupts, it’s called lava.
Key fact
About 1,350 volcanoes on land could erupt again.
Earthquakes
Earthquakes happen when rocks along a fault suddenly slip. Their size is measured on the magnitude scale, where each step means about 32 times more energy.
Key fact
The strongest recorded earthquake hit Chile in 1960: magnitude 9.5.
Rock Types
Rocks come in three types: igneous, from cooled magma; sedimentary, from layers of sediment; and metamorphic, changed by heat and pressure.
Key fact
Marble is limestone transformed by heat and pressure.
Pangaea
About 300 million years ago, the continents were joined in one supercontinent, Pangaea. It slowly broke apart into the continents we know.
Key fact
Africa and South America fit together like jigsaw pieces.
Fun facts
The inner core stays solid despite its heat, because the pressure there is millions of times that at the surface.
The summit of Mount Everest is made of limestone that formed on an ancient seabed.
A water molecule stays in the air for only about nine days, on average, before it falls again.
Iceland keeps gaining new land from its volcanic eruptions.
The 2011 Japan earthquake shifted Earth’s axis by around 10 cm and shortened the day by a tiny fraction of a second.
Pumice, a volcanic rock full of gas bubbles, is light enough to float on water.
The Atlantic Ocean is still getting wider, by a few centimetres every year.
Story: The Man Who Moved Continents
The Man Who Moved Continents
1912. German scientist Alfred Wegener notices that the coasts of South America and Africa fit like jigsaw pieces.
He argues the continents were once joined and have drifted apart. Most geologists scoff: what could possibly move them?
Wegener dies on a Greenland expedition in 1930. In the 1960s, maps of the seafloor show the continents really do move.
True or false?
Tap your answer to see if you got it, and why.
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Question 1 of 10
Earth’s outer core is liquid.
Show the answer
True. Molten iron and nickel, whose flow makes Earth’s magnetic field.
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Question 2 of 10
Many earthquakes happen near the edges of tectonic plates.
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True. That’s where plates grind, pull apart or collide.
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Question 3 of 10
Evaporation turns liquid water into vapour in the air.
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True. The Sun’s heat does most of the work.
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Question 4 of 10
Molten rock is called lava once it reaches the surface.
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True. Underground, it’s magma.
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Question 5 of 10
Each step up the magnitude scale means much more energy.
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True. About 32 times more.
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Question 6 of 10
Marble is a metamorphic rock.
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True. It forms from limestone.
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Question 7 of 10
The continents were once joined together.
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True. In the supercontinent Pangaea.
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Question 8 of 10
The crust is Earth’s thickest layer.
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False. It’s the thinnest, like the skin of an apple.
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Question 9 of 10
Earth’s tectonic plates never move.
Show the answer
False. They move a few centimetres every year.
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Question 10 of 10
Rain takes water out of the water cycle for good.
Show the answer
False. It flows back to the sea and evaporates again.
Keep going in the app
KnowSoda learns what you know and brings back what you’re about to forget. Planet Earth has 6 more ideas at the Advanced and Expert levels.
Sources
- USGS — Earthquake Hazards and Volcano Hazards programs
- British Geological Survey — Plate tectonics and the rock cycle
- NOAA — The water cycle
- Encyclopaedia Britannica — Earth’s interior, Pangaea
- U.S. Geological Survey — Yellowstone Volcano Observatory; Hawaiian hotspot
- Encyclopaedia Britannica — Kola Superdeep Borehole; geologic time
