Researchers have mapped out how life on Earth evolved over a billion years by studying ecosystems of fossil microbes.
Microbial eukaryotes called testate amoebae are poorly understood fossils from a time before complex multicellular life first evolved on our planet.
Eukaryotes are organisms whose cells have a membrane-bound nucleus. This group includes all animals and plants. Eukaryotes are one of the 3 major group of life forms on Earth, along with the 2 groups of prokaryotes: Bacteria and Archaea.
A new paper published in the Proceedings of the National Academy of Sciences focuses on testates to better understand the evolution of ecosystems on Earth and predict what the planet may look like in the future.
“Using fossils, we can estimate the divergence times and evolutionary paths leading to today’s testate amoebae found across the globe,” explains co-senior author Matthew Brown, a professor of biology at Mississippi State University in the US.
These organisms are also referred to as vase-shaped microfossils.
“Testates are particularly significant for understanding the history of early Earth and the history of life. They represent some of the earliest confirmed heterotrophic eukaryotes.”
Heterotrophic organisms are those which cannot produce their own food, unlike autotrophs like plants do through photosynthesis. Heterotrophs, instead, take their nutrition from other organic sources – in other words, eating other organisms.
The researchers used the information encoded in the genes of living organisms, coupled with fossil evidence, to examine the evolution of testates.
“From the data we collected, scientists can now examine the evolutionary history of these intriguing amoebae like never before through bioinformatic approaches called molecular clocks,” Brown says. “In evolution, genes and the proteins they encode evolve in a somewhat clock-like manner, making evolutionary changes somewhat predictable and model-able.”
Their results highlight key events in the history of life on Earth.
One of these is the origin of eukaryotes during the Stenian (1.2 to 1 billion years ago) and Tonian (1 billion to 720 million years ago) periods. Another is evidence which supports the suggestion of a “Tonian revolution” about 800 million years ago which saw the diversification of eukaryotes and the transition from a prokaryote-rich to eukaryote-rich ecosystems.
The authors write that the results also hint that, while early life on Earth is generally thought to have lived in the ancient oceans, “a terrestrial habitat for these organisms is also plausible” even before the planet froze over into “Snowball Earth” about 700 million years ago.
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