How was the Earth's

atmosphere first formed?

  by bacteria and other living things
  by gases from erupting volcanoes
  by water vapors

Today, what are the gas particles in our atmosphere MOSTLY made of?

  oxygen
  nitrogen
  volcanic gases

Today, scientist divide Earth's atmosphere into how many layers?

  three
  four
  two

Most of Earth's ozone is located in what layer?

  stratosphere
  mesosphere
  thermosphere

Which layer has temperatures that reach thousands of degrees Celsius?

  stratosphere
  mesosphere
  thermosphere