Author Question: What evidence of life on Earth before stromatolites do we have? What will be an ideal ... (Read 25 times)

stephzh · **on:** Jul 15, 2018

What evidence of life on Earth before stromatolites do we have? What will be an ideal response?

Question 2

What are stromatolites, and why are they important in Earth history? What will be an ideal response?

Kdiggy · **Reply #1 on:** Jul 15, 2018

Answer to Question 1

In Greenland, 3.8 billion-year-old rocks contain small carbon spheres that may be organic in origin,
but evidence is not conclusive. Archean and Early Paleoproterozoic rocks contain fossils of singlecelled
bacteria that lack a cell nucleus and reproduced asexually, called prokaryotic cells

Answer to Question 2

Stromatolites are blue-green algae that trap sediment. They are common in some Proterozoic rocks,
but the oldest are in 3.3 to 3.5 billion-year-old rocks. Stromatolites are important because the
atmosphere of the Paleoarchean had no free oxygen, but stromatolites release oxygen as a by-product
of photosynthesis. In the Archean and more so in the Proterozoic, they increased oxygen in Earth's
atmosphere.