Final answer:
Life on Earth began around 3.8 billion years ago, with solid evidence of actual cells found in stromatolites dating back to 3.5-3.95 billion years ago.
Step-by-step explanation:
The earliest evidence for life on Earth dates to about 3.8 billion years ago. This evidence comes from geochemical signatures found in the oldest surviving rocks formed around 3.9 billion years ago, which suggest life was already present. The first actual cells, with more solid geological evidence, date back to 3.5-3.95 billion years ago, notably in the form of stromatolites, which are large colonies built by microbial life.
During the Archaean Eon, these were significant life forms, indicating not just the presence of life but its interaction with the environment. Furthermore, fossil evidence of early life extends back to about 3.5 billion years ago, when these organisms had developed the sophistication to form stromatolites, a structure that has stood the test of time and is still found today.