When Did Life First Appear on Earth?
The holiday season is the time of the year when many people send out a newsletter providing friends and family members with updates of important events that have taken place over the course of the year.
This past year scientists have made some key advances in understanding an important event in history: the timing of life’s first appearance. (For a detailed discussion of Earth’s first life see the book Hugh Ross and I coauthored, Origins of Life.)
Since the publication of Origins of Life, I have written several articles updating our origins model with the latest discoveries about first life on Earth. (See: “Creation Model Passes Big Test,” “New Discovery Confirms Life’s Early Appearance on Earth,” “Experiencing How Early Life Lived,” and “Now Hear This! New Evidence for Ancient Life!)
Well, it’s time for another update! Good thing, too, because scientists have recently reported on two studies that shed insight onto the inaugural appearance of life on Earth.
When Did Life First Appear on Earth?
As discussed in Origins of Life, there are several geochemical signatures in the oldest rock formations that seem to indicate life (microbial bacteria and archaea) was present on Earth by at least 3.8 billion years ago. As corroboration, several other types of geochemical and a variety of fossil evidence for life have been recovered in slightly younger rock formations in South Africa and Western Australia, dating at around 3.5 billion years in age.
While many scientists find the evidence for early life on Earth compelling, there are a number who think that the geochemical markers and fossil structures are not bioauthentic. They agree that the evidence is consistent with what one would expect if life were present on early Earth, but the possibility that the geochemical residues and fossil remains were produced by some abiotic process can’t be ruled out. Instead the scientists argue that these signatures were actually created by nonbiological mechanisms that mimicked the chemical residues and structures generated by microorganisms.
Researchers hope that better characterization of existing geochemical and fossil markers will help determine what produced these residues and fossil-like structures. They also hope that additional finds will help resolve the controversy.
Discovery 1: Dolomite as a New Geochemical Marker for Life
The primary evidence for 3.8 billion-year-old life consists of carbonaceous deposits, such as graphite, found in rock formations in western Greenland. These deposits display an enrichment of the carbon-12 isotope. Other chemical signatures from these formations that have been interpreted as biological remnants include uranium/thorium fractionation and banded iron formations.
Recently, a team from Australia argued that the dolomite in these formations also reflects biological activity, specifically that of sulfate-reducing bacteria.1 The researchers present evidence that the dolomite was deposited from low-temperature seawater at the time the formations originated. These scientists suggest field studies and lab experiments have determined that dolomite can precipitate from seawater at low temperatures only if sulfate-reducing bacteria are present. These microbes consume sulfate, which inhibits dolomite precipitation. However, when these microbes are around, they remove the dolomite-precipitating inhibitor.
Collectively, these lines of evidence argue that the dolomite in the rocks of western Greenland resulted from the metabolic activity of sulfate-reducing microbes. The fact that previous work has uncovered separate evidence for sulfate-reducing microbes on early Earth adds further support for dolomite as a biogenic marker.
Discovery 2: Recovering New Microfossils
Investigators from Japan and Australia recently reported on the recovery of a new collection of microfossils from three separate localities of the Strelley Pool Formation in Western Australia.2 These microfossils include thread-like filaments believed to be remnants of chains of bacterial cells and the remains of biofilms secreted by bacteria. The scientists argue for the biogenicity of the fossils along a number of lines that include the fact that:
- microfossils were deposited at the time the formations originated;
- deposition occurred from a shallow-water environment;
- the composition of the microfossils is amorphous graphite;
- the size of the fossils is consistent with a microbial origin; and
- the variety of forms and their distribution in the rocks argues against an abiotic mechanism for their formation.
Early Life on Earth and RTB’s Model for the Origin of Life
These discoveries help firm up the evidence for early life on Earth. They also further affirm RTB’s origin of life model. Two key predictions of this model include: (1) life appearing on Earth, soon after the planet’s formation; and (2) first life possessing intrinsic complexity.
The discovery of new microfossils in formations at 3.5 billion years in age and the existence of ancient dolomite, formed by the mediation of sulfate-reducing bacteria, add to the weight of evidence that life has existed on Earth as far back as 3.8 billion years ago.
These discoveries also indicate that first life on Earth was metabolically complex. In the words of the researchers who discovered the first evidence for microbial sulfate reduction on early Earth, “Sulphate reduction is a complex metabolic process requiring advanced membrane-bound transport enzymes, proton motive force generation by ATPase and other charge separation proteins, and the genetic regulation of protein synthesis through DNA and RNA.”3
While the recognition that life appeared early in Earth’s history affirms the RTB model, it is unanticipated from an evolutionary perspective. In 1999, paleontologist J. William Schopf marveled that “no one had foreseen that the beginning of life occurred so astonishingly early.”4 No one, that is, from a naturalistic perspective.
- Allen P. Nutman et al., “≥3700 Ma Pre-Metamorphic Dolomite Formed by Microbial Mediation in the Isua Supracrustal Belt (W. Greenland): Simple Evidence for Early Life?” Precambrian Research 183, no. 4 (December 15, 2010): 725–37.
- Kenichiro Sugitani et al., “Biogenicity of Morphologically Diverse Carbonaceous Microstructures from the ca. 3400 Ma Strelley Pool Formation, in the Pilbara Craton, Western Australia,” Astrobiology 10, no. 9 (November 2010): 899–920.
- Yanan Shen, Roger Buick, and Donald E. Canfield, “Isotopic Evidence for Microbial Sulphate Reduction in the Early Archaean Era,” Nature 410 (March 1, 2001): 77–81.
- J. William Schopf, Cradle of Life (Princeton, NJ: Princeton University Press, 1999), 3.