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A phylogenetic tree of life shows that all major groups of organisms are linked to one common ancestor billions of years ago. This ancestor was probably a small single-celled organism that lived in an extreme environment. The rise of atmospheric oxygen led to the development of plants and animals (including humans). Without oxygen, life on Earth may have looked completely different.
Once life was established on the early Earth, it began to change the environment. Cyanobacteria released oxygen as a waste product of photosynthesis. The oxygen first reacted with dissolved iron in the oceans to create banded iron formations. At about 2.4 billion years ago, oxygen began to increase dramatically in the atmosphere (the Great Oxidation Event). This made multicellular life possible and created our protective ozone layer.
On the early Earth, microbial mats were everywhere! Some produced stromatolites, which are stubby pillars that later became fossilized. Stromatolites are not fossils of organisms but instead are the fossilized remains of layered sedimentary grains captured by the bacterial colony. This image shows modern stromatolites located in Shark Bay, Western Australia.
You can touch rocks that were formed by some of Earth’s oldest life. The larger stromatolite is 2.7 billion years old, while the smaller one is 2.3 billion years old. Their ages bracket the Great Oxidation Event (GOE). On the reverse side is a banded iron sample (2.45 billion years old).
THE COOLEST LIFE: Goddard scientists study the red and blue algae that live in glacier ice. The photo above shows samples being collected from Friedrichbreen glacier in Svalbard, Norway.
Scientists of the Goddard Center for Astrobiology study life found in extreme environments on Earth such as glacier ices, hydrothermal vents and alkaline lakes. For one research project, NASA scientists traveled to Svalbard, Norway, to study life that survives in very cold temperatures and in glacier ices. But you don’t always have to be a world traveler to study life under extreme conditions. Scientists can simulate some of these extreme conditions in the laboratory.
HEAT-RESISTANT BACTERIA: The vivid colors around the Grand Prismatic Spring in Yellowstone National Park result from microbial mats that grow around the edges of the water. Life can survive even at the hot temperature of 160 ºF (71 ºC). The boardwalk path on the lower right side indicates the size of this thermal vent.
Understanding how life survives in extreme environments informs and guides the search for life beyond Earth. The extreme environments on Earth may be analogous to those on different planets and moons. Thus, extraterrestrial life may exist even on a hot or cold planet.
The rise in oxygen was not entirely beneficial for life. It actually led to the near-extinction of oxygen-intolerant organisms.