The first evidence of the world’s oldest discovered glaciers has been found in the gold fields of South Africa. Extremely well-preserved glacial deposits lay beneath the world’s largest gold deposits, providing convincing evidence of the environmental conditions of the early Earth.
While the exact conditions of Earth during this period are still widely unknown, these 2.9-billion-year-old glacial remains could provide evidence for a number of theories surrounding conditions during this time. “It may be that this area was close to the poles. Another possibility is that the whole Earth was in a ‘snowball Earth’ period, when low atmospheric concentrations of CO2 and CH4 led to a ‘reverse greenhouse effect’, causing much of the planet to freeze,” said Professor Axel Hofmann, study co-author, in a statement.
“Scientists believe that this may have happened on a couple of occasions in the more recent past. If so, this would be the earliest such global cooling period recorded. Either possibility is scientifically interesting.”
Along with the physical evidence of fossilized glacial moraines – the debris left behind by glaciers – the team also analyzed oxygen isotope concentrations in the ancient rocks to determine the climate conditions at the time they were deposited.
“We looked at relative amounts of three 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,” explained study co-author Professor Ilya Bindeman. “Couple that geochemical evidence with the moraine evidence, and it means glaciers, the oldest glaciers yet found on Earth.”
The significance of the location of the finding, beneath the Earth’s largest sedimentary gold deposits, may also spark further investigation explained Hofman. “It’s possible that a change from icehouse to greenhouse conditions may have aided in the formation of those gold deposits, but this needs to be confirmed and requires further work.”
The use of triple oxygen isotope analysis in this way could add new avenues for finding evidence of the early Earth’s glaciation, with finds like this introducing new lines of questioning and investigation into Earth’s historical climate.
The study is published in Geochemical Perspectives Letters.