Scientists have long agreed that early Earth had extreme climate variations, but recent scientific discoveries provide new evidence supporting the theory.
Researchers Prof. Axel Hofmann and Prof. Ilya Bindeman have found well-preserved glacial deposits in rocks underneath the world’s largest gold deposits in South Africa. The deposits have been dated as 2.9 billion years old, based on the ages of the rocks surrounding them — the oldest glaciers yet found on Earth.
“This is one of the few areas which remain fairly intact and unchanged from the early Earth,” Prof Bindeman explained.
The glacial deposits are fossilized glacial moraines — the material left behind by glaciers as they move. The bulk of this material is typically soil and rock. By analyzing the oxygen isotopes found in these deposits, the researchers concluded that the deposits were made during a time with icy temperatures. This, taken with the shape and type of deposits found, indicate the presence of glaciers.
The study authors have a few possible theories for why the glaciers were found in this part of the world. "It may be that this area was close to the poles,” said study co-author Axel Hofmann. “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. 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,” Hofmann continued.
The researchers were able to identify ancient climate conditions using triple oxygen isotope analysis, looking at the relative amounts of three oxygen isotopes, 16O, 17O, and 18O. These three types of oxygen have different weights, allowing scientists the ability to then analyze materials’ origin.
"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,” explained Dr. Andrey Bekker of University of California, Riverside. “Triple oxygen isotope analysis adds an entirely new line of evidence to this argument.”
Sources: Geochemical Perspectives Letters; Phys.org
