What is the oldest known living organism on Earth?

The oldest known living organism on Earth is a type of bacteria called cyanobacteria or blue-green algae, which have been around for about 3.5 billion years. These single-celled organisms are believed to be the first photosynthetic organisms on the planet, responsible for releasing oxygen into the atmosphere and paving the way for the evolution of complex life forms. Cyanobacteria are found in a variety of habitats, from the open ocean to hot springs and even in Antarctic ice.

Scientists have identified some individual colonies of cyanobacteria that are believed to be more than 2 billion years old. These ancient organisms are known as stromatolites, which are structures built by layers of sediment and cyanobacteria. Stromatolites are still found today in a few places around the world, such as Shark Bay in Western Australia.