_____________ is an essential element of all living creatures.

The total amount of the carbon on Earth is constant.

Carbon is used in the process called __________ by plants and algae to make food and the building blocks for growth.

Bacterias that decompose dead plants release _____________ back into the atmosphere.

In the oceans; algae, plants, and other organisms use carbon from the atmosphere for ________________.

Organisms that die in the ocean may __________ to the bottom and form limestone rock of a period of time.

Ocean coral and oysters use carbon to create _________.

Limestone is a type of rock created from the ______________ of dead sea organisms.

Over ________________ of years, once-living matter that remains in the ground can transform into fossil fuels.

Since the mid- 1800's, _____________ activity has significantly altered the carbon cycle.

Burning fossil fuels has raised the concentration of ___________ in the atmosphere.