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Trace fossils of stromatolites date to Precambrian time. What are stromatolites?

A.
mounds of calcium carbonate deposited by cyanobacteria

B.
bacteria that lived near hydrothermal vents in the ocean floor

C.
soft-bodied animals, such as worms and jellyfish

D.
small burrows made by worms or worm-like animals

1 answer

A. mounds of calcium carbonate deposited by cyanobacteria

Stromatolites are layered structures formed by the activities of cyanobacteria, which are photosynthetic microbes. They create mounds or mats made up of calcium carbonate and other minerals, which are deposited over time, often found in shallow marine environments.