TellUs: "The Earth Story" Series, Meteorites & First Signs of Life

The Earth’s Story Series: The Hadean and Archaean Eons

Leading on from my last blog I thought it’d be fun to go more in depth about each of the eons and eras briefly mentioned, describing what the Earth looked like at these times, whether the Earth was inhabited, what the atmosphere was like and so forth. Throughout the next few weeks I’ll be going over the multiple eons and eras in our Earth’s history, from the beginning until present day. Starting off we will be discussing the Hadean and Archaean eons!

Hadean Eon

Here we start with the Earth being newly formed around about 4600 million years ago. It appears to be an extremely hostile territory for any life-form. Meteor strikes are common, volcanic activity is prevalent and there is no ozone layer. This means there is no protection from the Sun’s harmful radiation. However the Sun at this point was actually cooler than it is today, but the Earth would still be too hot for comfort without that ozone layer. For 1000 million years no life appears. It isn’t surprising that this eon is named after the Greek god of the underworld, Hades, for its ‘hell-ish’ feel.

Archaean Eon

This eon begins around 3600 million years ago and finishes approximately 2500 million years ago. This is an exciting eon because the first life begins to appear! Bacteria is this first life-form that appears. The earliest traces of life (bacteria) were found, preserved as tiny patterns in a rock formation which is known as “chert”. This was dated to be around 3600 million years old, hence why we have an eon change from Hadean. This bacteria lived in the newly formed oceans, providing the environment for early life and for life much after this. 

Earliest form of bacteria,
"Chert"

Also early continents begin to appear. This is a sign deep within the Earth that the mechanisms that build continents, mountain ranges and oceans have began!

Both the Hadean and Archaean eon atmospheres were similar, with carbon dioxide and methane dominating the atmosphere. Little oxygen was present. However we begin to see the bacteria affecting the atmosphere, by releasing nitrogen. 

Halfway through this eon, around 3000 million years ago, a key event happens! A huge event! Cyanobacteria aka blue-green algae appears! This may not sound overly exciting, but I promise it is. It’s exciting because here we begin to see the algae using photosynthesis. This means the raging carbon dioxide in the atmosphere can start to be taken in and oxygen then being released. This event changes the Earth’s atmosphere forever! Remains of this algae has been found in mound-like formations name “stromatolites”. What’s amazing is that this algae still flourishes in today’s lakes and oceans!

Cyanobacteria in its mound-like
formation, "Stromatolites"

By the end of these eons, nearly half of the Earth’s history has passed.