After analyzing rock beds situated near Durban on the east coast of South Africa, containing glacial deposits estimated 2.9 billion years old, scientists have uncovered evidence of the oldest glaciers ever found. The University of Johannesburg archaean geologist Axel Hofmann led the team.
The team discovered the traces of the world’s oldest known glaciers, dating from 2.9 billion years ago. This suggests that South Africa’s largest gold reserves are buried beneath rocks.
This implies that continental ice caps were present at the time, either because the region was closer to the poles or because parts of the Earth may have been frozen during a previously unrecognized “snowball Earth” period of freezing weather. Following a recent peer-reviewed publication, this work is presented for the first time at the Goldschmidt geochemistry conference in Lyon.
According to scientists, the early Earth’s climate must have undergone significant fluctuations, but compelling proof of the precise circumstances has been difficult to come by.
Researchers Professor Axel Hofmann from the University of Johannesburg in South Africa and Professor Ilya Bindeman from the University of Oregon in the United States have now discovered physical proof as well as evidence from relative oxygen isotope concentrations in ancient rocks, showing clear evidence of glaciers, 2.9 billion years ago.
Ilya Bindeman said, “We found extremely well-preserved glacial deposits close to the gold fields of South Africa. This is one of the few areas which remain fairly intact and unchanged from the early Earth. These deposits are fossilized glacial moraines, the debris a glacier leaves as it gradually melts and contracts. These are the oldest moraine deposits ever found. In addition, we were able to correlate this with analysis of oxygen isotopes from these rocks, which showed that the climate must have been cold when the rocks were deposited”.
“We looked at relative amounts of 3 oxygen isotopes, 16O, 17O, and 18O. These are all types of oxygen but have very slightly different weights. We found that these rocks had very low amounts of 18O, and very high amounts of 17O, indicating that they were formed at icy temperatures. This means ice. Couple that geochemical evidence with the moraine evidence, meaning glaciers, the oldest glaciers yet found on Earth.”
The researchers proposed the following theories as potential explanations:
Axel Hofmann said, “It’s possible that this location was near the poles. A “snowball Earth” epoch during which low atmospheric CO2 and CH4 concentrations caused a “reverse greenhouse effect” and caused much of the world to freeze is another scenario. According to scientists, this may have occurred a few times in the recent past. If correct, this would be the world’s first recorded cooling period. Both possibilities have a scientific interest.”
“The largest sedimentary gold deposits in the world are found in slightly younger rocks sitting above the rocks we studied. It’s possible that a change from icehouse to greenhouse conditions may have aided in forming those gold deposits, but this needs to be confirmed and requires further work.”
Commenting, Dr. Andrey Bekker (Associate Professor at the Department of Earth & Planetary Sciences, University of California, Riverside) said:
“Evidence for glaciation of this age has been hotly discussed and debated for decades based on sedimentological evidence with suggestions ranging from high altitude to high latitude glaciation. Triple oxygen isotope analysis adds a new line of evidence to this argument. The biogeochemical carbon cycle controls not only climate but also atmospheric oxygen content, and these data are likely to trigger follow-up studies on the transient oxygenation at that time”.
Journal Reference:
- A. Hofmann, I.N. Bindeman. Earth’s first glaciation at 2.9 Ga was revealed by triple oxygen isotopes. Geochemical Perspectives Letters v26. DOI: 10.7185/geochemlet.2319