Earth’s surface over four billion years ago was more or less like the oceanic-crust researchers have said based on a study that found Earth’s oldest ever rock dated 4.02 billion years old.
The study published in the journal Nature Geoscience claims with strong evidence that Earth was in a solid state 4 billion years ago and that its surface was largely like an oceanic crust. While multiple studies have pointed out that rocks on Earth formed more than four billion years ago, there were hardly any concrete proofs that could establish this fact with certainty. However, researchers have managed to give proof this time around with a 4.02 billion year old rock wherein is present well-preserved grains of the mineral zircon.
Jesse Reimink, a post-doctoral fellow at the Carnegie Institute for Science in the US, found the sample during a fieldwork trip from an area roughly 300 kilometres north of Yellowknife in Canada. Reimink explains that zircon retains its chemical signature and records age information that doesn’t get reset by later geological events, while the rock itself records chemical information that the zircon grains don’t.
Chemistry of the ancient rock isn’t all that different from the rocks forming today in Iceland, which is transitional between oceanic and continental crust. In fact, Iceland has been hypothesised as an analog for how continental crusts started to form.
“We examined the rock itself to analyse those chemical signatures to explore the way that the magma intrudes into the surrounding rock,” Reimink said.
One signature in particular recorded the assimilation step of magma from Earth’s crust, researchers said. “While the magma cooled, it simultaneously heated up and melted the rock around it, and we have evidence for that,” Reimink said.
Currently only three locations are known to exist with rocks or minerals older than 4 billion years old: one from Northern Quebec, mineral grains from Western Australia, and the rock formation from Canada’s Northwest Territories examined in this study.