Sorted by weight
What Is Inside the Earth?
Earth is layered because when it was molten, heavy stuff sank and light stuff floated.
-
Step 1 of 5
Early Earth was completely molten.
Constant collisions during formation kept the whole planet liquid. Everything could move freely — and that is when the layers were set.
-
Step 2 of 5
Heavy metal sank to the middle.
Iron and nickel are dense, so they sank through the liquid rock and collected at the centre. That is Earth's core, and it is still there.
-
Step 3 of 5
Lighter rock floated to the top.
Silicon and oxygen compounds are much lighter, so they rose and formed the mantle and eventually the thin crust we stand on.
-
Step 4 of 5
The crust is astonishingly thin.
Under the oceans it is around 6 km; under continents up to 70. Compared with Earth's 6,371 km radius, that is thinner than an apple's skin.
-
Step 5 of 5
We know this from earthquake waves.
Nobody has drilled past 12 km. But earthquake waves bend and reflect at each boundary, and reading those echoes maps the interior.
The inner core is solid iron despite being hotter than the Sun's surface — the pressure is simply too great to melt.
The short version
Earth is layered because a molten young planet let heavy iron sink and light rock float, and earthquake waves prove it.
Try it yourself
Shake oil, water and honey in a jar and let it settle. It sorts itself by density — young Earth, in a jar.
Topics