Scientists can use a variety of clues to figure out what’s beneath the Earth’s surface without actually having to dig – including bombarding minerals found in beach sand with superfine lasers thinner than a human hair.
This technique has been used in a new study that points to a 4-billion-year-old piece of Earth’s crust the size of Ireland that lay beneath Western Australia and influenced the geological evolution of the area over millions of millennia.
There could be clues as to how our planet went from being uninhabitable to being livable.
The researchers believe that the vast crustal area would have greatly influenced rock formation as old materials mixed with new, having first emerged as one of the planet’s earliest protocrustal formations and having survived multiple mountain-building events.
“When we compare our results with existing data, it appears that many regions around the world experienced a similar timing of early crustal formation and preservation,” says Maximilian Dröllner, PhD student in geology and lead author from Curtin University in Australia.
“This indicates a significant shift in Earth’s evolution about 4 billion years ago, when meteorite bombardment subsided, the crust stabilized, and life began to establish itself on Earth.”
The lasers were used to vaporize grains of the mineral zircon extracted from sand collected from rivers and beaches in Western Australia.
Technically known as laser ablation split-stream inductively coupled plasma mass spectrometry, the method allows scientists to date the grains and compare them to others to see where they might have come from.
This gave the team a glimpse of the crystalline basement beneath the Earth’s surface in that particular region – showing where the grains originally eroded, what forces were used to create them, and how the region’s geology had evolved over time.
Aside from the importance of the extant protocrustal remnant — about 100,000 square kilometers (38,610 sq mi) of it — the block’s boundaries will also help scientists discover what else is hidden beneath Earth’s surface and how it might have evolved in its current state .
“The rim of the ancient piece of crust appears to define an important crustal boundary that controls where economically important minerals are found,” says lead researcher, Curtin University geologist Milo Barham.
“Detecting these ancient crustal remnants is important for the future of optimized sustainable resource exploration.”
As might be expected, after 4 billion years there is not much of the original earth’s crust left to study, which makes such findings all the more interesting and useful for experts – and gives us an important window into the distant past.
The shifting of the Earth’s crust and the turbulence of the hot mantle beneath it are difficult to predict and retrospectively map. Therefore, if evidence of internal movement and geology can be found at the surface, scientists are keen to exploit it.
Going forward, the results of the study described here could also help scientists studying other planets – the way these planets are formed, how their earliest crust is formed, and even how extraterrestrial life might colonize them.
“Studying early Earth is challenging given the tremendous amount of time that has elapsed, but it is fundamental to understanding the importance of life on Earth and our quest to find it on other planets,” says Barham.
The research was published in the journal TerraNova.