Stromatolites in are in the news.

First appearing over 3 billion years ago, stromatolites are the oldest known fossils. They were colonial structures built by photosynthesising blue-green algae, and were responsible for the creation of earth's oxygen atmosphere. These organisms thrived in warm aquatic environments, building reefs much as corals do today.
The photograph is a slice through a relatively young, 120 million year old, stromatolite from the Mendip hills.
Now there is a claim that stromatolites have been found in ancient rocks from Greenland. These rocks were part of the seafloor 3.7 billion years ago, and if confirmed as stromatolites, the  colonies would predate the previously oldest known fossils by over 200 million years.
We live in exciting times!