- Science
- The Earth
- Earth Timeline
- Early life: Oxygen enters the atmosphere
Early life: Oxygen enters the atmosphere
Exactly when the first life on Earth - the ancestors of modern bacteria - began is a subject of debate, but evidence suggests it could be as much as 3.5 billion years ago.
Early bacterial life introduced oxygen to the atmosphere. As the first free oxygen was released through photosynthesis by cyanobacteria, it was initially soaked up by iron dissolved in the oceans and formed red coloured iron oxide, which settled to the ocean floor. Over time, distinctive sedimentary rocks called banded iron formations were created by these iron oxide deposits. Once the iron in the oceans was used up, the iron oxide stopped being deposited and oxygen was able to start building up in the atmosphere about 2.4 billion years ago.
Image: Stromatolites in Shark Bay, Western Australia. Stromatolites, which are formed by microscopic bacteria, are rare on Earth today but were much more common in the ancient Earth's seas. (credit: L Newman & A Flowers/SPL)
Introduction
Early life: Oxygen enters the atmosphere
TV clips (5)
play
Oxygen enters the atmosphere
Stromatolites pump oxygen into the early atmosphere.
Dr Iain Stewart explains how stromatolites, one of the earliest forms of life, first released oxygen over three billion years ago when they turned sunlight into energy. Oxygen was initially soaked up by iron in the seas but eventually entered the atmosphere.
play
The early Earth in a flask
The famous Miller-Urey experiment investigates the first steps towards life.
In the 1950s, Stanley Miller and Harold Urey, scientists at the University of Chicago, exposed a sealed flask full of the inorganic chemicals that may have been present in the atmosphere of the early Earth to an electrical current. Amino acids, the organic chemical precursors to proteins, were generated. They showed that it was theoretically possible for lightning strikes in an atmosphere full of their inorganic ingredients to generate some of the organic precursors to life. Many scientists now think that the early Earth may have had an atmosphere with a different composition to the one that Miller and Urey experimented with.
play
Wading in an ancient sea
Aubrey Manning visits the stromatolites of Shark Bay, Australia.
Aubrey Manning talks to Professor Maarten De Wit about the stromatolites in Shark Bay, Australia. Stromatolites are mounds in shallow seas formed by millions of bacteria and are among the most ancient forms of life on Earth.
play
Rusty rocks
Early life affected the structure of the planet.
Presenter Aubrey Manning and geologist Professor Maarten De Wit investigate iron rich rocks known as banded iron formations, which formed when stromatolites, some of the earliest known life forms on Earth, produced oxygen that combined with iron dissolved in the oceans.
play
Volcanoes and life
Volcanoes may have played an important role in the emergence of life.
Dr Iain Stewart explains how volcanic activity on the early Earth may have played an important role in the emergence of life about four billion years ago. He visits hot springs in Rotorua, New Zealand, to meet Dr Bruce Mountain, who explains the theory.
Early life: Oxygen enters the atmosphere
The Great Oxygenation Event (GOE), also called the Oxygen Catastrophe or Oxygen Crisis or Great Oxidation, was the biologically induced appearance of free oxygen (O2) in Earth's atmosphere. This major environmental change happened around 2.4 billion years ago.
Photosynthesis was producing oxygen both before and after the GOE. The difference was that before the GOE, organic matter and dissolved iron chemically captured any free oxygen. The GOE was the point when these minerals became saturated and could not capture any more oxygen. The excess free oxygen started to accumulate in the atmosphere.
The rising oxygen levels may have wiped out a huge portion of the Earth's anaerobic inhabitants at the time. Cyanobacteria, by producing oxygen that was toxic to anaerobic organisms, were essentially responsible for what was likely the largest extinction event in Earth's history.[citation needed] Additionally the free oxygen reacted with the atmospheric methane, a greenhouse gas, triggering the Huronian glaciation, possibly the longest snowball Earth episode ever. Free oxygen has been an important constituent of the atmosphere ever since.
This entry is from Wikipedia, the user-contributed encyclopedia. If you find the content in the 'About' section factually incorrect, defamatory or highly offensive you can edit this article at Wikipedia.
Related Earth topics
Other related BBC topics
What happened...
The Late Heavy Bombardment ends 
Snowball Earth Collections
News
Warning over 'dangerous' Skipsea cliff erosion
… that the cliffs were not safe, she said....
Elsewhere on the web
BBC links
BBC © 2012 The BBC is not responsible for the content of external sites. Read more.
This page is best viewed in an up-to-date web browser with style sheets (CSS) enabled. While you will be able to view the content of this page in your current browser, you will not be able to get the full visual experience. Please consider upgrading your browser software or enabling style sheets (CSS) if you are able to do so.