Stromatolites are a major constituent of the fossil record of the first forms of life on earth. The earliest fossils date to 3.7 billion years ago.

Stromatolites are not only Earth's oldest of fossils but are intriguing in that they are our singular visual portal into deep time on earth, the emergence of life, and the evolving of the beautiful forms of life of the modern times.

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According to livescience, Earth is about 4.5 billion years old, but the oldest rocks still in existence date back to just 4 billion years ago. A set of filament-like fossils from Australia, reported in the journal Astrobiology in 2013, may be the remains of a microbial mat that might have been extracting energy from sunlight some 3.5 billion years ago. Another contender for world's oldest life is a set of rocks in Greenland that may hold the fossils of 3.7-billion-year-old colonies of cyanobacteria, which form layered structures called stromatolites.

Proposal for Formation of Archaean #Stromatolites before the Advent of Oxygenic Photosynthesis. Via @CellEvo https://t.co/xd8TWetg82 pic.twitter.com/TRUaOTIECs

— Lukas Novak (@animalculum) November 16, 2016

In broad terms, stromatolites are fossil evidence of the prokaryotic life that remains today, as it has always been, the preponderance of biomass in the biosphere. For those that subscribe to the theory of the living earth, it is the prokaryotes that maintain the homeostasis of the earth, rendering the biosphere habitable for all other life.

#Stromatolites at Yalgorup National Park, #Australia these is the first known life on #Earth, 3.45 billion years old pic.twitter.com/VKBDsL9KVY — José Joaquín Galán (@JJoaquinGalan) February 2, 2017

The researchers first reported in 1996 in the journal Nature that isotopes in those rocks might indicate ancient metabolic activity by some mystery microbe. Those findings have been hotly debated ever since as, in fact, have all claims of early life.