Earth's 1st (?) Mass Die-Off: End of the Great Oxidation Event (ca. 2.0 Billion Years Ago)

[EnolaGaia]

We're all luckier than we previously thought ...

Strongly suggestive (though admittedly indirect) evidence indicates the earliest microbial life on earth suffered a mass die-off event that (proportionally) makes the "Great Dying" (Permian Extinction Event) and the K-T Boundary Event (the dinosaurs' demise) pale by comparison.

Ancient die-off greater than the dinosaur extinction

When significant oxygen entered the atmosphere, ancient life multiplied. But after a few hundred million years, Earth's oxygen plummeted, resulting in a die-off likely greater than the extinction of the dinosaurs.

Clues from Canadian rocks formed billions of year ago reveal a previously unknown loss of life even greater than that of the mass extinction of the dinosaurs 65 million years ago, when Earth lost nearly three-quarters of its plant and animal species.

Rather than prowling animals, this die-off involved miniscule microorganisms that shaped the Earth's atmosphere and ultimately paved the way for those larger animals to thrive.

"This shows that even when biology on Earth is comprised entirely of microbes, you can still have what could be considered an enormous die-off event that otherwise is not recorded in the fossil record," said Malcolm Hodgskiss, co-lead author of a new study published in Proceedings of the National Academy of Sciences.

Invisible clues

Because this time period preceded complex life, researchers cannot simply dig up fossils to learn what was living 2 billion years ago. Even clues left behind in mud and rocks can be difficult to uncover and analyze.

Instead, the group turned to barite, a mineral collected from the Belcher Islands in Hudson Bay, Canada, that encapsulates a record of oxygen in the atmosphere. Those samples revealed that Earth experienced huge changes to its biosphere -- the part of the planet occupied by living organisms -- ending with an enormous drop in life approximately 2.05 billion years ago that may also be linked to declining oxygen levels. ...

FULL STORY: https://www.sciencedaily.com/releases/2019/08/190828180437.htm

 

[EnolaGaia]

Here's the bibliographic data and Abstract for the published paper ...

A productivity collapse to end Earth’s Great Oxidation

Malcolm S. W. Hodgskiss, Peter W. Crockford, Yongbo Peng, Boswell A. Wing, and Tristan J. Horner
PNAS August 27, 2019 116 (35) 17207-17212; first published August 12, 2019 https://doi.org/10.1073/pnas.1900325116

Edited by Mark H. Thiemens, University of California San Diego, La Jolla, CA, and approved July 8, 2019 (received for review January 21, 2019)


The Great Oxidation Event (GOE) ca. 2,400 to 2,050 Ma caused the first significant accumulation of free oxygen in the atmosphere and potentially a dramatic growth of oxidant reservoirs on the Earth’s surface in a suggested “oxygen overshoot.” However, the termination of this event remains poorly understood. Here, we present geochemical data suggesting a drastic decline in gross primary productivity across the end-GOE transition, delineating a shift from “feast” to “famine” conditions characteristic of the next 1 billion y.

Abstract

It has been hypothesized that the overall size of—or efficiency of carbon export from—the biosphere decreased at the end of the Great Oxidation Event (GOE) (ca. 2,400 to 2,050 Ma). However, the timing, tempo, and trigger for this decrease remain poorly constrained. Here we test this hypothesis by studying the isotope geochemistry of sulfate minerals from the Belcher Group, in subarctic Canada. Using insights from sulfur and barium isotope measurements, combined with radiometric ages from bracketing strata, we infer that the sulfate minerals studied here record ambient sulfate in the immediate aftermath of the GOE (ca. 2,018 Ma). These sulfate minerals captured negative triple-oxygen isotope anomalies as low as ∼ −0.8‰. Such negative values occurring shortly after the GOE require a rapid reduction in primary productivity of >80%, although even larger reductions are plausible. Given that these data imply a collapse in primary productivity rather than export efficiency, the trigger for this shift in the Earth system must reflect a change in the availability of nutrients, such as phosphorus. Cumulatively, these data highlight that Earth’s GOE is a tale of feast and famine: A geologically unprecedented reduction in the size of the biosphere occurred across the end-GOE transition.

SOURCE: https://www.pnas.org/content/116/35/17207