New estimate predates earliest fossil evidence by 800 million years.
An exhaustive genetic analysis of modern-day organisms has revealed new insights into Earth’s earliest forms of complex life.
The findings, reported by MIT earth scientists in Nature, suggest that eukaryotes — the domain of life comprising animals, plants, and protists — were present on Earth as early as 2.33 billion years ago, right around the time when oxygen became a permanent fixture in the atmosphere.
This new time-stamp for ancient life significantly predates the earliest sign of eukaryotes found in the fossil record —1.56 billion-year-old macroscopic fossils that scientists widely agree are the remains of multicellular algae-like organisms.
The MIT researchers arrived at their estimate not by examining rocks for fossil evidence but by using a technique called “molecular clock analysis.”
This approach involves first sifting through DNA databases to trace the evolution of particular gene sequences across hundreds of modern species.
Then, using ages derived from the fossil animal and plant relatives, these sequences can be tied backward in time to the earliest point at which those sequences must have been expressed in ancestral eukaryotes.
“We’ve again demonstrated the feasibility of using modern DNA to provide insights about early life,” says Roger Summons, professor of geobiology in MIT’s Department of Earth, Atmospheric and Planetary Sciences (EAPS).
“We have no concrete records of early life. We have a few fossil microbes, which are often disputed, and some geochemical signals, but it’s not enough to reconstruct an informed history of life. What we’re saying is, you can look at what’s on the planet today, and you can tell something important about what the organisms’ ancient ancestors were doing.”
The analysis was carried out by Summons and lead author David Gold, a former MIT postdoc who is currently at Caltech, along with Abigail Caron, a senior research support associate at MIT, and Gregory Fournier, the Cecil and Ida Green Career Development Assistant Professor in EAPS.
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News source: MIT. The content is edited for length and style purposes.
Figure legend: This Knowridge.com image is credited to MIT.