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From Soup to Cells—the Origin of Life

A microbe-like cellular filament found in 3.465 billion year old rock
A microbe-like cellular filament found in 3.465 billion year old rock
Evolution encompasses a wide range of phenomena: from the emergence of major lineages, to mass extinctions, to the evolution of antibiotic resistant bacteria in hospitals today. However, within the field of evolutionary biology, the origin of life is of special interest because it addresses the fundamental question of where we (and all living things) came from.

Many lines of evidence help illuminate the origin of life: ancient fossils, radiometric dating, the phylogenetics and chemistry of modern organisms, and even experiments. However, since new evidence is constantly being discovered, hypotheses about how life originated may change or be modified. It's important to keep in mind that changes to these hypotheses are a normal part of the process of science and that they do not represent a change in the basis of evolutionary theory.

When did life originate?
Evidence suggests that life first evolved around 3.5 billion years ago. This evidence takes the form of microfossils (fossils too small to be seen without the aid of a microscope) and ancient rock structures in South Africa and Australia called stromatolites. Stromatolites are produced by microbes (mainly photosynthesizing cyanobacteria) that form thin microbial films which trap mud; over time, layers of these mud/microbe mats can build up into a layered rock structure — the stromatolite.

Stromatolites are still produced by microbes today. These modern stromatolites are remarkably similar to the ancient stromatolites which provide evidence of some of the earliest life on Earth. Modern and ancient stromatolites have similar shapes and, when seen in cross section, both show the same fine layering produced by thin bacterial sheets. Microfossils of ancient cyanobacteria can sometimes be identified within these layers.

stromatolites at Shark Bay close up of a stromatolite at Shark Bay
Modern stromatolites in Shark Bay, Australia

cross section of fossil stromatolites cross section of fossil stromatolites
Cross sections of 1.8 billion year old fossil stromatolites at Great Slave Lake, Canada

Where did life originate?
Hydrothermal vent photo
A hydrothermal vent at the bottom of the ocean
Scientists are exploring several possible locations for the origin of life, including tide pools and hot springs. However, recently some scientists have narrowed in on the hypothesis that life originated near a deep sea hydrothermal vent. The chemicals found in these vents and the energy they provide could have fueled many of the chemical reactions necessary for the evolution of life. Furthermore, using the DNA sequences of modern organisms, biologists have tentatively traced the most recent common ancestor of all life to an aquatic microorganism that lived in extremely high temperatures — a likely candidate for a hydrothermal vent inhabitant! Although several lines of evidence are consistent with the hypothesis that life began near deep sea vents, it is far from certain: the investigation continues and may eventually point towards a different site for the origin of life.
Explore further
•  How did life originate?
•  Looking for the oldest fossils
•  Studying the origin of life
•  Human evolution

• Apex Chert microbe-like cellular filament image provided by J. William Schopf.
• Shark Bay stromatolite photos provided by Carole Hickman.
• Great Slave Lake stromatolite photos provided by PF Hoffman.
• Hydrothermal vent photo courtesy of Verena Tunnicliffe, University of Victoria.
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