Question

What are the four systems that sustain life on earth? What threat do they face?

Answer 1

Answer:

The earth has four principal biological systems. These are: fisheries, forests, grasslands and croplands. They form the basis of the world's economic system.

Explanation:

The earth has four principal biological systems. These are: fisheries, forests, grasslands and croplands. They form the basis of the world's economic system.

Answer 2

Answer:

The earth has four principal biological systems. These are: fisheries, forests, grasslands and croplands. They form the basis of the world's economic system. They supply us food and raw materials for industry.