Early Earth was largely covered with an oceanic crust-like surface unlike the continental crust that researchers had expected to find, suggests a new study.
"It gives us important information about how the early continents formed. Because it’s so far back in time, we have to grasp at every piece of evidence we can. We have very few data points with which to evaluate what was happening on the Earth at this time," said Jesse Reimink, researcher at the University of Alberta, in Canada, of the study that examined the world’s oldest rock unit estimated to be 4.02 billion years old.
Only three locations worldwide exist with rocks or minerals older than four billion years old — Northern Quebec, mineral grains from Western Australia and the rock formation from Canada’s Northwest Territories which was examined for the study. Earth is estimated to have been created 4.5 billion years ago.
Reimink’s study found the presence of well-preserved grains of the mineral zircon during fieldwork in an area roughly 300 km north of Yellowknife.
"Zircons lock in not only the age but also other geochemical information that we’ve exploited in this paper. Rocks and zircon together give us much more information than either on their own," Reimink added.
Zircon retains its chemical signature and records age information that does not get reset by later geological events, while the rock itself records chemical information that the zircon grains do not, the study suggested.
The researchers explain that the chemistry of the rock itself looks like rocks transitional between oceanic and continental crust and examined to analyse those chemicals that the magma intrudes into the surrounding rock.
"While the magma cooled, it simultaneously heated up and melted the rock around it, and we have evidence for that," Reimink said.
According to the study, published in the journal Nature Geoscience, the presence of continents above water and exposed to the atmosphere has huge implications in atmospheric chemistry and the presence or absence of life.
The amount of continents on the Earth has a large chemical influence both on processes in the deep Earth (mantle and core) and at the Earth’s surface (atmosphere and biosphere).