A team of scientists has discovered traces of the world’s oldest known glaciers, dating back 2.9 billion years, in rocks found beneath the world’s largest gold deposits in South Africa. The traces suggest that at the time that area was closer to the poles, or had experienced a previously unknown period of extreme cold.
The researchers’ findings were presented at the Goldschmidt geochemistry conference in Lyon. Scientists generally agree that there must have been great variations in the climate of the early Earth, but it has been difficult to find concrete evidence that would clarify exactly what the Planet’s climatic conditions were at that time.
Now researchers Professor Axel Hofmann (University of Johannesburg, South Africa) and Professor Ilya Bindeman (University of Oregon, USA) have found evidence from the relative concentrations of oxygen isotopes in ancient rocks, as well as physical evidence, showing the presence, in the area of their study, of glaciers 2.9 billion years ago.
Ilya Bindeman said, “We found extremely well-preserved glacial deposits near the gold deposits in South Africa. This is one of the few areas that remain fairly intact and unchanged since the age of the primeval Earth. These deposits are fossilized glacial moraines, which are basically the debris left behind by a glacier as it gradually melts and contracts. These are the oldest moraine deposits ever found. In addition, we were able to correlate them with oxygen isotope analysis of these rocks, which showed that the climate must have been cold when the rocks were deposited.”
“We looked at the relative amounts of 3 oxygen isotopes, 16 O, 17 O and 18 O. These are all types of oxygen but have slightly different weights. We found that these rocks had very low amounts of 18 O and very high amounts of 17 O, indicating that they were formed at glacial temperatures. That means ice. Couple that geochemical evidence with the moraine evidence, and it means glaciers, the oldest glaciers ever found on Earth.”