Scientists have made a groundbreaking discovery, finding traces of the world’s oldest known glaciers dating back 2.9 billion years. These glacier remnants were found in rocks beneath South Africa’s largest gold deposits, indicating the presence of ancient continental ice caps. This suggests that either the region was once located closer to the poles or that Earth experienced a previously undocumented period of extreme cold known as “snowball Earth.”
This significant finding is discussed in the article “Earth’s first glaciation at 2.9 Ga revealed by triple oxygen isotopes” by A. Hofmann and I.M. Bindeman, published in Geochemical Perspectives Letters. The authors will present their work, titled “A model of unidirectional and accumulative fluxes from mantle to the lithosphere explaining crustal growth via triple oxygen isotope mass balance throughout Earth’s history,” at the Goldschmidt geochemistry conference in Lyon.
While it is widely accepted among scientists that the early Earth’s climate experienced significant variations, concrete evidence has been challenging to obtain. However, researchers Professor Axel Hofmann and Professor Ilya Bindeman have now provided physical proof and relative oxygen isotope concentrations in ancient rocks, which solidify the existence of glaciers 2.9 billion years ago.
Professor Ilya Bindeman explains, “We have discovered exceptionally well-preserved glacial deposits near South Africa’s gold fields. These deposits are fossilized glacial moraines, the remnants of debris left by glaciers as they gradually melt and recede. They represent the oldest moraine deposits ever found. Additionally, oxygen isotope analysis of these rocks reveals that the climate must have been cold when they formed.”
Professor Axel Hofmann adds, “We examined the relative amounts of three oxygen isotopes—^16O, ^17O, and ^18O. These isotopes have slightly different weights. Our findings indicate that these rocks contained low levels of ^18O and high levels of ^17O, suggesting their formation under icy conditions. When considering the geochemical evidence alongside the moraine deposits, it becomes evident that these are the oldest glaciers ever discovered on Earth.”
The researchers propose two explanations for these findings. “One possibility is that this region was once located near the poles. Another hypothesis is that Earth experienced a ‘snowball Earth’ period, characterized by low atmospheric concentrations of CO2 and CH4 that caused a reverse greenhouse effect, leading to a global freeze. Similar events have been theorized to occur in more recent history. Regardless, both possibilities are scientifically intriguing,” states Professor Hofmann.
He further adds, “Interestingly, the largest sedimentary gold deposits in the world are found in slightly younger rocks above the ones we studied. It is possible that the transition from icehouse to greenhouse conditions played a role in the formation of these gold deposits, but further research is needed to confirm this.”
Dr. Andrey Bekker, Associate Professor at the Department of Earth & Planetary Sciences, University of California, Riverside, comments on the significance of the researchers’ work, stating, “Triple oxygen isotope analysis provides an entirely new line of evidence in the discussion and debate on glaciation of this age. The biogeochemical carbon cycle not only influences climate but also atmospheric oxygen content, making these findings likely to spur further studies on transient oxygenation during that time period.”
More information: A. Hofmann et al, Earth’s first glaciation at 2.9 Ga revealed by triple oxygen isotopes, Geochemical Perspectives Letters (2023). DOI: 10.7185/geochemlet.2319
Provided by Goldschmidt Conference
Citation: Scientists find evidence of world’s oldest glaciers (2023, July 13) retrieved 13 July 2023 from https://phys.org/news/2023-07-scientists-evidence-world-oldest-glaciers.html
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