Which layer contains Earth's most diverse set of plant and animal life?

• A. Atmosphere
• B. Hydrosphere
• C. Geosphere
• D. Biosphere

Answer: (D)

The variety of life on Earth happens in the biosphere, the global realm where living organisms exist and interact. It includes plants and animals on land, in freshwater, and in the oceans, as well as organisms that live in the air. Because it encompasses all environments that can support life, the biosphere hosts the widest range of species and ecosystems. The other layers describe parts of Earth without focusing on living organisms: the atmosphere is the air around the planet, the hydrosphere is all Earth’s water, and the geosphere is the solid and rocky surface. But life thrives across the biosphere, making it the layer with Earth's most diverse plant and animal life.