prize9-7, Exercise 3: The "missing" Precambrian record

Model answer (check the details):

The Precambrian covers about 88% of Earth's history, but its fossil record is thin. Reasons: most life was soft-bodied and microscopic, with no shells or bones to preserve easily; many Precambrian rocks have been deeply buried, heated and metamorphosed, which destroys fossils; and old surface rocks have been eroded or recycled by plate tectonics.

Other evidence: stromatolites (layered structures made by microbial mats), microfossils in fine-grained rock, chemical signs of life such as isotope ratios of carbon, and chemical changes in rocks showing oxygen building up in the atmosphere. Radiometric dating gives the ages.

Care: "missing" means sparse and hard to read, not absent, and research is active.