• Are some minerals more plentiful than others?
  Many useful minerals are abundant. Other less common, but important ...

• What common rocks are used for buildings?
  Two sedimentary rocks, limestone and sandstone, and the igneous rock ...

• How are fossils turned to stone?
  When tree trunks or bones are buried, minerals deposited from water ...

• Do earthquakes and volcanoes occur in the same places?
  Most active volcanoes occur near the edges of plates that are moving ...

• What is carbonization?
  Leaves usually rot quickly after plants die. But sometimes they float ...

• When did mammals first appear?
  Mammals lived on Earth from at least the start of the Jurassic ...

• When did people first live on Earth?
  Hominids (ape-like creatures that walked upright) first appeared on ...

• What are plates?
  The Earth's hard outer layers are divided into large blocks called ...

• How big are the plates?
  The Earth's outer layers are split into seven large plates and about ...

• What happens when plates collide?
  Along deep ocean trenches, one plate is pulled beneath another. There ...