Earth's 4 Spheres

Earth's biosphere is composed of all of the living organisms on the planet. This includes all of the plants, animals, bacteria, fungi and single-celled organisms found on Earth.

Most of this life exists no deeper than about 10 feet into the ground or about 600 feet above it.

Because each individual is so small in relation to the overall planet, organisms are often grouped into biomes, which are regional communities characterized by vegetation and climate. You are likely already familiar with some of these, like:

• deserts
• grasslands
• rainforests

The biosphere has existed for about 3.5 billion years.

The biosphere’s earliest life-forms, called prokaryotes, survived without oxygen. Ancient prokaryotes included single-celled organisms such as bacteria and archaea.

Some prokaryotes developed a unique chemical process. They were able to use sunlight to make simple sugars and oxygen out of water and carbon dioxide, a process called photosynthesis. These photosynthetic organisms were so plentiful that they changed the biosphere. Over a long period of time, the atmosphere developed a mix of oxygen and other gases that could sustain new forms of life.

The addition of oxygen to the biosphere allowed more complex life-forms to evolve. Millions of different plants and other photosynthetic species developed. Animals, which consume plants (and other animals) evolved. Bacteria and other organisms evolved to decompose, or break down, dead animals and plants.

The biosphere benefits from this food web. The remains of dead plants and animals release nutrients into the soil and ocean. These nutrients are re-absorbed by growing plants. This exchange of food and energy makes the biosphere a self-supporting and self-regulating system.

The biosphere is sometimes thought of as one large ecosystem—a complex community of living and nonliving things functioning as a single unit. More often, however, the biosphere is described as having many ecosystems.