14. Earth's Prebiotic Atmosphere

Around more than 3 billion years ago, our Earth's atmosphere originally had almost no free oxygen. It was gradually changed to what it is today, over a very long time duration of a process called Great Oxygenation Event which means it is a long process of the introduction of free oxygen into the earth's atmosphere by a single celled photosynthesizing microbe called Cyanobacteria. They were the first organisms to make free oxygen into the atmosphere by photosynthesis process and it took a very long time from about three billion years to one billion years ago.

   

As Cyanobacteria produced oxygen, and built their stromatolites, they changed the environment for other protists. Since the other protists had no way to deal with oxygen, as they were the earth's anaerobic inhabitants, most of them would have become extinct. Stromatolites are layered mounds, columns and sheets-like sedimentary rocks that were originally formed by the growth of layer upon layer of cyanobacteria. Fossilized stromatolites provide records of ancient life on Earth.

 

Fossilized Stromatolites found in Glacier National Park

 In 2002, a scientific study showed that the 3.45 billion years old geological formations of Precambrian Stromatolites from Glacier National Park, Canada contain fossilized cyanobacteria which was later suggests that they are evidence of one of the oldest and earliest lifeforms on Earth at the time. Therefore, if life originated on earth, then this happened sometime between 4.4 billion years ago, when water vapor first liquefied and 3.5 billion years ago. After through a few years of searching and further discoveries of the fossilized evidences at different geological location, it was claimed that the earliest life on earth existed more than 3.5 billion years ago, during the Eoarchean Era when sufficient crust had solidified following the molten Hadean Eon period of Earth.

Hydrothermal Vents in Nuvvuagittug Greenstone Belt of Quebec in Canada

  

The earliest habitats for microbial life on Earth formed in Hydrothermal Vents

 
In 2017, microorganisms or microfossils were discovered in iron and silica rocks which were once hydrothermal vents in the Nuvvuagittuq Greenstone Belt of Quebec in Canada which was announced as old as 4.28 billion years old and that is the oldest records of life ever on earth. This provided support for the hypothesis that abiogenesis began near hydrothermal vents and it suggests “an instantaneous emergence of life after the ocean formation around 4.41 billion years ago, which was not so long after the formation of Earth. And if life arose quickly on Earth, then it could be common in the Universe. A few scientists think if the origin of life could be common in the Universe, then it would be a possibility that life might have been carried from planet or from outside the solar system by the transport of spores. This idea is known as 'Panspermia'.