The earth's oldest existing lifeforms

Scientists estimate that the earth is around 4.5 billions years old. In Western Australia, you can see stromatolites, rock formations built by organisms beginning about 3.5 billion years ago. And those organisms are still with us. 

With a citizen scientist's understanding, stromatolites are stony structures built by colonies of microscopic photosynthesising organisms called cyanobacteria. — Read the rest