Constraining the Time Interval for the Origin of Life on Earth

Abstract

Estimates of the time at which life arose on Earth make use of two types of evidence. First, astrophysical and geophysical studies provide a timescale for the formation of Earth and the Moon, for large impact events on early Earth, and for the cooling of the early magma ocean. From this evidence, we can deduce a habitability boundary, which is the earliest point at which Earth became habitable. Second, biosignatures in geological samples, including microfossils, stromatolites, and chemical isotope ratios, provide evidence for when life was actually present. From these observations we can deduce a biosignature boundary, which is the earliest point at which there is clear evidence that life existed. Studies with molecular phylogenetics and records of the changing level of oxygen in the atmosphere give additional information that helps to determine the biosignature boundary. Here, we review the data from a wide range of disciplines to summarize current information on the timings of these two boundaries. The habitability boundary could be as early as 4.5 Ga, the earliest possible estimate of the time at which Earth had a stable crust and hydrosphere, or as late as 3.9 Ga, the end of the period of heavy meteorite bombardment. The lack of consensus on whether there was a late heavy meteorite bombardment that was significant enough to prevent life is the largest uncertainty in estimating the time of the habitability boundary. The biosignature boundary is more closely constrained. Evidence from carbon isotope ratios and stromatolite fossils both point to a time close to 3.7 Ga. Life must have emerged in the interval between these two boundaries. The time taken for life to appear could, therefore, be within 200 Myr or as long as 800 Myr. Key Words: Origin of life-Astrobiology-Habitability-Biosignatures-Geochemistry-Early Earth. Astrobiology 18, 343-364.

The Hot Spring Hypothesis for an Origin of Life

“…Inset B shows an example of such a pool on Mount Mutnovsky, an active volcano in Kamchatka, Russia (Kompanichenko et al, 2015). The recent discovery of a 3.5billion-year-old hot spring setting on a volcanic plateau that formed in the absence of direct plate tectonic involvement is a good analog for an early Earth volcanic landscape emerging from a global ocean just 500 million years after the approximate time frame we are proposing for life's origins (Pearce et al, 2018;Van Kranendonk et al, 2020).…”

Colloquium: Physical constraints for the evolution of life on exoplanets

“…The general conclusion that can be drawn (from the above examples) is that planets in the HZ of very lowmass stars are often, but not always, susceptible to losing their atmospheres over sub-Gyr timescales, even reaching a minimum of O 10 7 yrs. On Earth, we know that the timescale taken for the origin of life (abiogenesis) was ≤ 0.8 Gyr (Pearce et al, 2018), and it required 4.5 Gyr for the emergence of technological intelligence, namely, Homo sapiens. Strictly speaking, we have no knowledge whatsoever of what the timescale for abiogenesis is on other planets based on just a single data point from Earth (Spiegel and Turner, 2012).…”

Active Galactic Nuclei: Boon or Bane for Biota?

“…This result is consistent with more sophisticated analyses that have yielded an average AGN lifetime of ∼ 4.5 × 10 8 yrs provided that M BH < 10 8 M and ∼ 1.5 × 10 8 yrs for M BH > 10 8 M (Marconi et al 2004); in some instances, a total lifetime of ∼ 10 9 yrs for the active phase is feasible. The earliest unambiguous evidence for life on Earth is attributable to carbon isotopic (δ 13 C) signatures and stromatolite-like structures from the Isua supracrustal belt in west Greenland that date to 3.7 Ga (Pearce et al 2018), but other ambiguous signatures have been dated to 4.1-4.3 Ga (Bell et al 2015;Dodd et al 2017). 7 Thus, based on empirical evidence, we can say with some degree of confidence that life originated within 8 × 10 8 yrs after the Earth became habitable with the possible upper bound being as small as ∼ 2 × 10 8 yrs.…”