A thin shell of air, water, and land - called the biosphere - holds all of life on earth. The biosphere measures just 20 km (12 miles) from top to bottom and contains three very different environments. The atmosphere is the air we breathe. It also filters harmful radiation from the sun while letting heat and light pass through. The hydrosphere consists of all the water on earth. The water circulates through the entire biosphere in a never-ending cycle. The lithosphere is earth’s rocky outer shell, including the continents and the ocean floor. Soil on the surface of the lithosphere supports the growth of plants and trees. Together, these three spheres provide the support system for life on earth.

 

Air
Cirrus clouds, formed from frozen water vapour high in the atmosphere, are an early sign that storms may be on the way.

 

Water
More than 97 percent of all the water on earth is held in the world’s oceans, whose average depth is 4 km (2.5 miles).

 

Land
Soil in the lithosphere plays a vital role in cycling water and other nutrients through the biosphere.

 

The Water cycle
The water in the hydrosphere is constantly in motion. The sun evaporates water from the oceans. This water vapor collects in clouds, then falls back to earth as rain. Rivers and streams carry the water back to the ocean.

 

BIOSPHERE
Life abounds in the biosphere, thanks to the interaction of land, air, and water. Earth is the only planet known to contain all three of these life-giving spheres.

 

 

Lithosphere
Earth’s outer shell is broken into about a dozen large pieces, called tectonic plates, that float over the molten rock below. The plates’ movement is slowly rearranging the continents at a rate of about 3 cm (1 inch) per year.

 

Atmosphere
The atmosphere can be divided into five distinct layers. Each layer is thinner in density until it fades 900 km (560 miles) above the earth’s surface. Oxygen and nitrogen make up almost 98 percent.

 

Hydrosphere
Covering about 75 percent of our blue planet, the hydrosphere regulates earth’s climate by soaking up heat from the sun and moving it around the globe through ocean currents.