Final answer:
Evidence for early microbial life includes fossilized microbial mats, isotopic ratios, stromatolites, and chemical signatures in ancient rocks, dating back about 3.5 billion years.
Step-by-step explanation:
The different lines of evidence for early microbial life on Earth include fossilized microbial mats, isotopic ratios in geological deposits, stromatolites, and chemical signatures in ancient rocks. For instance, one of the key evidence is the existence of fossilized microbial mats, which are similar to those found near modern hydrothermal vents, dating back to approximately 3.5 billion years ago.
This, along with laboratory experiments such as those conducted by Stanley Miller and Harold Urey, which demonstrated the possible formation of organic compounds from inorganic molecules, supports the natural origin of life on Earth.