The oldest known form of life is debated, but the current leading contender is stromatolites. These are layered, rock-like structures formed by the activity of cyanobacteria, also known as blue-green algae.

Here's what we know:

* Fossil evidence: Stromatolite fossils have been found in Western Australia, dating back to 3.48 billion years ago. This makes them the oldest known evidence of life on Earth.

* Cyanobacteria: Stromatolites are formed by the layered growth of cyanobacteria. These are photosynthetic organisms that produce oxygen as a byproduct. This means that stromatolites played a crucial role in oxygenating the Earth's atmosphere, paving the way for the evolution of more complex life.

* Other contenders: While stromatolites are the oldest known form of life, other forms of microbial life may have existed even earlier. However, due to the lack of fossil evidence, it's difficult to definitively say when and how these earlier forms of life arose.

It's important to note that research on the origins of life is ongoing. Scientists are constantly discovering new clues and refining their understanding of early life on Earth.