What is the age of the earliest traces of life on Earth?
Fossils are our strongest, and to most people most accessible, evidence of the great age of life on earth. The fossils in the Burgess Shale are clearly the imprints of critters, but are a mere 505 million years old. The oldest cyanobacteria-like fossils known are nearly 3.5 billion years old, among the oldest fossils currently known. There is Evidence for biogenic graphite in early Archaean Isua metasedimentary rocks, but requires knowledge of isotopic chemistry to understand (or dispute.) Life on earth originated before 3.5 billion years ago.