
Out-of-This-World Hypothesis
Date: Monday, April 23 @ 10:46:11 CDT Topic: 3. Space News
The rise and fall of species on Earth might be driven in part by the undulating motions of our solar system as it travels through the disk of the Milky Way, scientists say.
Two years ago, scientists at the University of California, Berkeley found the marine fossil record shows that biodiversity—the number of different species alive on the planet—increases and decreases on a 62-million-year cycle. At least two of the Earth’s great mass extinctions—the Permian extinction 250 million years ago and the Ordovician extinction about 450 million years ago—correspond with peaks of this cycle, which can’t be explained by evolutionary theory.
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Now, a team of researchers at the University of Kansas (KU) have come up with an out-of-this-world explanation. Their idea hinges upon the fact that, appearances aside, stars are not fixed in space. They move around, sometimes rushing headlong through galaxies, or approaching close enough to one another for brief cosmic trysts.
In particular, our Sun moves toward and away from the Milky Way’s center, and also up and down through the galactic plane. One complete up-and-down cycle takes 64 million years— suspiciously similar to Earth’s biodiversity cycle.
Galactic bow shock
The KU researchers independently confirmed the biodiversity cycle and have proposed a novel mechanism by which the Sun’s galactic travels is causing it.
Scientists know the Milky Way is being gravitationally pulled toward a massive cluster of galaxies, called the Virgo Cluster, located about 50 million light years away. Adrian Melott and his colleague Mikhail Medvedev, both KU researchers, speculate that as the Milky Way hurdles towards the Virgo Cluster, it generates a so-called bow shock in front of it that is similar to the shock wave created by a supersonic jet.
“Our solar system has a shock wave around it, and it produces a good quantity of the cosmic rays that hit the Earth. Why shouldn’t the galaxy have a shock wave, too?” Melott said.
The galactic bow shock is only present on the north side of the Milky Way’s galactic plane, because that is the side facing the Virgo Cluster as it moves through space, and it would cause superheated gas and cosmic rays to stream behind it, the researchers say. Normally, our galaxy’s magnetic field shields our solar system from this “galactic wind.” But every 64 million years, the solar system’s cyclical travels take it above the galactic plane.
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