Earth’s journey through the Milky Way may have had a profound impact on the geology of our planet. New research indicates that every 200 million years, as Earth passes through the spiral arms of its galaxy, the planet is struck by high-energy comets, and this bombardment can thicken Earth’s continental crust.
The team behind the new findings believe the dense gas clouds in the spiral arms interact with comets on the side of the solar systemsending them rushing to Earth.
“As geologists, we normally think that internal Earth processes are really important to the evolution of our planet,” said Chris Kirkland, a geologist at Curtin University in Australia and lead author of the study describing the results. statement (opens in a new tab). “But we can also think on a much larger scale and look at extraterrestrial processes and our place in the galactic environment.”
Related: Earth’s oldest crystals reveal the age of plate tectonics
The team reached their conclusion by examining zircon crystals from two of Earth’s oldest continents and regions, where the planet’s oldest continental history is preserved: the North American craton, in Greenland, and the Pilbara Craton, Western Australia.
The decay of uranium in zircon crystals in these regions has been used to create a geological timeline spanning 1 billion years, from 2.8 billion to 3.8 billion years ago, during the eon archaean. This timeline could help geologists discover how Earth became the only planet known to have continents and active plate tectonics.
Isotopes of the element hafnium in zircon allow scientists to pinpoint periods in Earth’s history that saw an influx of juvenile magma – magma containing elements that have never reached the surface before – a sign crust formation.
Kirkland and his team found that over a long period of time, crust production patterns matched galactic years. (A galactic year is the time it takes for the sun to complete one orbit around the center of the Milky Way.) These findings were supported by examinations of oxygen isotopes, which revealed a similar pattern.
Therefore, Earth’s journey around the galactic center helps shape the planet’s geology, the team concluded.
Earth’s journey around the Galactic Center
Not only does the solar system move around the galactic center, but the spiral arms radiating from it also rotate, albeit at a different rate.
The sun orbits the galactic center at about 536,000 mph (863,000 km/h), while the spiral arms spin at about 47,000 mph (76,000 km/h). This means that the sun and the solar system, along with many other stars in the Milky Way, spiral in and out of the arms, much like fans doing “the wave” in a stadium.
When the solar system enters the spiral arms, icy planetesimals in the Oort Cloud at its outer edge (about 4.6 trillion miles, or 7.4 trillion kilometers, from the Sun) interact with the dense gas clouds of the whip-like arms, sending icy material hurtling toward the inner solar system — and our planet.
These objects arrive with more energy than asteroids which regularly bombard the Earth. Most of these space rocks come from the main asteroid belt between March and Jupitera region much closer to Earth than the Oort Cloud is.
“This is important because more energy will lead to more melting,” Kirkland said in the statement. “When it hits, it causes greater amounts of decompression melting, creating greater uplift of the material.”
The influence of impacts on rock formation and increased crust generation was also apparent in the team’s examination of spherule beds, which are deposits of small spheres created by ejected material that cools, condense and fall back to Earth after the impacts. The spherule beds were also correlated with Earth’s passage through the dense spiral arms of the Milky Way about 3.3 billion to 3.5 billion years ago, when the planet was just over a billion years.
Determining the age of more deposits in the spherule beds could further support the team’s findings and, in turn, encourage geologists and astrophysicists to start thinking more about the influence of Earth’s larger cosmic environment on the planet’s geology.
“It’s very hard to prove these things; we want to make that connection and start the conversation to look at the geological processes beyond Earth, beyond the solar system, and what might be driving them,” the co said. – author of the study, Phil Sutton, speaker. in astrophysics at the University of Lincoln in the UK “We didn’t just train in isolation.”
The team’s findings were published online Aug. 23 in the journal Geology.
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