Scientists think oceans may have formed after millions of years of


What bodies in the solar system collided and combined to form Earth?

Carbon dioxide and water vapor.

Scientists think that earth's first atmosphere was made up of

Gravity and heat.

What factors caused the shape and structure of the earth?


Early life-forms released oxygen into the earth's atmosphere through the process of


The layer of earth that has the lightest elements is the


The middle layer of earth is the

Heavier and lighter elements separated.

Earth's layers formed as rocks melted and


The layer of earth that extends to the planet's center is the