A 4-billion year old piece of Earth’s crust the size of Ireland has been detected beneath Western Australia according to new research. However this piece of crust is not the oldest. The oldest is in the Canadian Shield on the eastern shore of Hudson Bay which is 4.3 billions years old. The Earth is 4.5 billion years old.
Because Earth’s crust is constantly being churned up and pushed back into the mantle by plate tectonics, most of the planet’s rocky surface was formed within the past couple billion years.
However, the oldest crust that has been discovered, like the recently found chunk in Western Australia, dates back around 4 billion years. That suggests that something novel occurred in that era of Earth history, study coauthor Maximilian Droellner said.
“When comparing our findings to existing data, it appears many regions around the world experienced a similar timing of early crust formation and preservation,” said Droellner. “This suggests a significant change in the evolution of the Earth some four billion years ago, as meteorite bombardment waned, crust stabilized and life on Earth began to establish.”
Geochemical hints in the sediments near the region suggested that there might be even older crust buried under newer rocks and sediments at the surface.
To learn where these minerals came from, the researchers used data collected by Earth orbiting satellites. Since Earth’s crust varies in thickness, gravity varies slightly across the surface of the planet. By measuring these gravity variations, scientists can figure out how thick the crust is in different locations.
Understanding the formation of crust 4 billion years ago will help researchers understand how the continents first formed. This period lay the foundation for the planet as it is today, but few hints of the earliest Earth have survived the constant upheaval of the planet’s surface.
https://www.livescience.com/4-billion-year-old-crust-australia