Arya News - Some of the planet`s oldest volcanic rocks can still be found in Western Australia.
Major clues to the origins of our planet—and life itself—are locked inside some three billion-year-old volcanic rocks from Western Australia. These ancient rocks show that water was likely already shaping Earth’s interior and driving volcanic activity over three billion years ago.
The findings published today in the journal suggest that Earth was already running a version of the water-recycling processes that shape our planet today, even though our home planet was a dramatically different place billions of years ago. Geologists found signs that roughly three billion years ago water traveled deep beneath the Earth’s surface, helping to create the magmas that formed volcanoes like the ones found in the Pacific’s explosive Ring of Fire today.
Every single day, Earth’s water is continually recycled through a process called plate tectonics . Ocean water is carried down into the Earth’s middle layer, or mantle . The water is then pulled down at subduction zones. In these zones, one tectonic plate slides beneath another, feeding volcanoes that are powerful enough to build continents. However, billions of years ago, that internal water recycling process worked completely differenly—if at all.
“The early Earth was too hot for plates to behave that way [pulling water down to the mantle],” Dr. Eric Vandenburg , a study co-author and geochemist at Australia’s Adelaide University, said in a statement. “So until now it has been unclear whether surface water could have made that journey more than three billion years ago, and if so, how.”
In other words, it may have been too hot for Earth’s early plates to move water down to the mantle the way it does today.
To learn more, the team studied rocks from Western Australia’s Pilbara Craton . The rocks were formed between 3.6 billion and 2.8 billion years ago and are some of Earth’s oldest. The iron-rich rocks began forming before there was oxygen in Earth’s atmosphere—or even life itself. The Pilbara remains one of the few places where geologists can study the young Earth.
This image shows part of the Hamersley Basin in Western Australia, which lies on the southern Pilbara Craton. A craton is the stable, geologically inactive core of an ancient continent. The Pilbara Craton has remained intact, surviving the affronts of plate tectonics and erosion since the Archean Eon (four billion to 2.5 billion years ago).
The team analyzed the chemical fingerprints preserved within the Pilbara Craton rocks and reconstructed events that occurred 3.1 billion years ago. Surprisingly, they found evidence that large amounts of water had already made its way deep into the Earth’s interior. All of that water also influenced the formation of volcanic rocks. The team believes that while modern plate tectonics may not have existed on Earth yet, a different process may have been bringing water into the mantle.
So, how was water getting so deep into the Earth without plate tectonics? The team proposes it was because of a mechanism they call dripduction . During dripduction, dense water-rich sections of the Earth’s cool outer crust sporadically sag and then collapse into the hotter mantle below. As these pieces of crust collapsed, they brought water down with them. The water was then released into the Earth’s mantle, creating magmas that fed volcanic eruptions. When magma interacts with water, the intense heat turns that water into steam . The steam then expands and erupts along with the magma. That magma then solidified into rocks that geologists still study today.
“The Earth wasn’t operating exactly as it does now, but it appears some of the key processes were already in place,” Vandenburg said.
For geologists, understanding when water first started moving deep underground helps explain one of our planet’s most critical processes. Plate tectonics influence everything from volcanic eruptions and continental growth. Shifting plates may even produce some of the chemical elements that are necessary for life to exist at all. These findings provide clues about how the Earth’s continents formed, and how our planet evolved into what we know today.
According to the team, these new findings suggest that Earth’s interior and surface may have been connected much earlier than we thought. Earth appears to have been a surprisingly dynamic young planet that was already recycling one of its most crucial ingredients: water.