Easy. Answer is oxygen because it says which one was missing before any life was on earth. And in order to have life on earth you need oxygen!
:)
Answer:
The animals could change it. For example, a bunny could dig a hole in the ground, making a home for other animals inside of it, too, changing the animals' living environment.
Or natural disasters could change their environment, too. For example, if a landslide occurred and covered a pond, frogs and snakes could lose their living areas and food, which would make them have to move to a different area, changing another ecosystem.
Answer:
the formation of new cells for the replacement and repair of old cells as well as for growth.
Explanation:
Explanation:
Physics The state of a body or physical system that is at rest or in constant and unchanging motion. The sum of all forces acting on a body that is in equilibrium is zero (because opposing forces balance each other).
