History of Earth . There are microbial mat fossils such as stromatolites found in 3.48 billion-year-old sandstone discovered in Western Australia . Microbial mat . Microbial mats are the earliest form of life on Earth for which there is good fossil evidence , from , and have been the most important members and maintainers of the planet 's ecosystems .
The History of Earth rules out microbial mat fossils being part of it.