Blue-green algae
Also called: Cyanobacteria · Topic: Origin and Evolution of the Earth and the Solar System · NCERT: Class 11, Ch 2 "The Origin and Evolution of the Earth"
Meaning
Blue-green algae, also called cyanobacteria, are microscopic living things that make their own food by photosynthesis (using sunlight to turn carbon dioxide and water into food, which gives off oxygen). Structures closely like them are found in rocks older than about 3,000 million years. Their layered mats hardened into rock mounds called stromatolites, and some of these are about 3.5 billion years old. They released oxygen, first into the oceans and later into the air. This made later life possible.
Example
At Jhamarkotra, near Udaipur in Rajasthan, old rocks hold fossil stromatolites. These rock layers were built up by ancient blue-green algae.
Don't confuse with
- True algae (such as seaweeds): their cells have a nucleus. Cyanobacteria are bacteria, with simpler cells that have no nucleus, even though they are called "algae".