In 1980, Walter Alvarez and colleagues at the University of California have discovered a thin layer of clay in the Earth's crust, clay containing a surprising amount of iridium, a rare chemical element.
Researchers have advanced the hypothesis that the iridium-rich layer is evidence of a massive impact of a comet that hit our planet ago 66 million years and would have led to extinction of the dinosaurs.
Alvarez suggested that the iridium-rich layer was formed after a huge cloud of dust to litter the Earth's surface due to the impact. The cloud of dust covered the planet, sinking it in the dark and lowering the temperature. In 1990, a crater with a diameter of 100 meters was discovered in Mexico's Yucatan Peninsula, the researchers believe that it confirms the impact of comet described by Alvarez.
The moment when the impact occurred, along with fossil evidence has led many researchers to conclude that the extinction of dinosaurs and other life forms was generated by this collision.
Subsequent studies led to the discovery of other mass extinctions of the geological past of the planet who all appear to have resulted from such collisions. Moreover, these "coincidences" occurred every 30 million years.
The researchers believe that these cycles are caused by Earth's position in the galaxy "Milky Way".
Our galaxy is best understood as a huge disc. Our solar system revolves in 250 million years, the circumference of the disc, but the path is not smooth, but "waving". Earth passes every 30 million years, the middle plane of the disc, says researcher Michael Rampino.
In his view, impact and extinction cycles occur when the Sun and planets in our solar system become the center "crowded" the disc of our Galaxy.
Normally, comets orbiting the Sun at the end of the solar system, far from Earth, but when our system runs through Agomer disc, the gravitational pull of stars, interstellar clouds and dark matter disturbs comets trajectory, and some may reach Earth orbit or may strike our planet.
These cycles of 30 million years can explain and other geological phenomena, the researcher said. These include volcanic eruptions, forming mountains, changing magnetic fields or major changes in sea levels.
Specifically, when the Earth passes through the central disk of the galaxy, the planet's path is "pieces" dense dark matter. Dark matter particles can be captured by the Earth, specifically the core of our planet. If dark matter density is high enough, the particles will annihilate each other, which will increase the heat kernel and thus to increased geological activity.
Clues to Earth's geological history support the theory that astrophysical phenomena such as those that would dictate geological and biological evolution of our planet, says Rampino.
He also points out that the Earth passes in the last million years, the disc "dense" of our Galaxy.
Source: IFL Science
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