Question

Be able to explain what stromatolites are and their abundance through geologic time.

a) Fossilized footprints of early animals; rare in the Precambrian
b) Microbial structures in sedimentary rocks; abundant in the Archean and Proterozoic
c) Early land plants; common in the Jurassic
d) Glacial deposits; widespread during the Pleistocene

Answer 1

Stromatolites are layered sedimentary structures formed by prokaryotes that represent the oldest known record of life on Earth, abundant in the Archean and Proterozoic eons, with some modern examples still found today.

Step-by-step explanation:

Stromatolites are fossilized microbial mats that are considered the earliest record of life on Earth. These sedimentary structures are formed by minerals precipitated out of water by prokaryotes within a microbial mat. They form layered rocks made primarily of carbonate or silicate. Historically, stromatolites have been abundant in the Archean and Proterozoic eons and are of significant interest as they played a pivotal role in the oxygenation of the Earth's atmosphere. While stromatolites are mainly known as ancient fossils, with the oldest known being 3.47 billion years old, modern equivalents are still forming in certain locations such as the Anza-Borrego Desert State Park in San Diego County, California, and in Western Australia.