Final answer:
The earliest definite evidence for life on Earth dates back to 3.5-3.95 billion years ago, during the Archaean Eon. There is also softer evidence of microbial life as old as 4.1 billion years ago, near the end of the Hadean Eon.
Step-by-step explanation:
The earliest definite evidence for life on Earth exists in solid geological evidence that dates back to 3.5-3.95 billion years ago, during the Archaean Eon. There is also softer evidence of microbial life in the form of graphite and other possible remains as old as 4.1 billion years ago, near the end of the Hadean Eon. The presence of life on Earth as early as 4.1 billion years ago is supported by geological and geochemical evidence.