Origin and evolution of the biosphere

The first prokaryotes flourished in an oxygen-free biosphere some 3.8 billion years ago. These primitive ancient prokaryotes included single-celled creatures such as bacteria and archaea. Some prokaryotes evolved a distinctive chemical process known as photosynthesis and converted water and carbon dioxide into simple sugars and oxygen with the help of sunlight. The organism’s ability to perform photosynthesis is autotrophy. More species, therefore, were able to use the carbon dioxide in the atmosphere and eventually supplied the atmosphere with oxygen. These creatures ranged from single-celled algae to multicellular autotrophs, such as vascular plants.

The atmosphere gradually changed into a mixture of oxygen and other gases that could support new types of life. More complex living forms were able to evolve as a result of the biosphere receiving more oxygen, such that they acquired different ecological niches. Numerous species of plants and other photosynthetic organisms, which formed the autotrophs of the food chain, increased. Likewise, animals that eat plants or other animals that behave as heterotrophs also developed. Also, to decompose dead plants and animals, bacteria and fungi (decomposers) evolved.