Astronomy 2021A/B Study Guide - Midterm Guide: Tidal Locking, Dna Replication, Mariner 4

• School: Western University
• Department: Astronomy
• Course: Astronomy 2021A/B
• Professor: Prof

Document Summary

For example, a 3. 5-billion-year-old fossil tells us that life on earth arose before 3. 5 billion years ago. Because the geological record is incomplete and because we may not yet have discovered the oldest intact fossils, we do not know exactly how long life has existed on earth. Stromatolites- from the greek word for rock beds . Characterized by a distinctive layered structure, in size, shape, and interior structure, ancient stromatolites look virtually identical to sections of mats formed today by colonies of microbes sometimes called living stromatolites . Living stromatolites contain layers of sediment intermixed with different types of microbes, microbes near the top generate energy through photosynthesis those beneath use organic compounds left as waste products by the photosynthetic microbes. There is some controversy about the biological origin of stromatolites, because geological processes of sedimentation can mimic their layering.