Earth may have been exposed to interstellar clouds which may have changed the chemistry of the planet's atmosphere and led to the development of multiple ice ages, researchers suggest.
Astrophysicists from Boston University, Harvard University and Johns Hopkins suggest that around two million years ago, our solar system encountered an interstellar cloud so large and dense that Earth was exposed to radiation that altered its climate.
Although deep freezes occur for many reasons—including the tilt of the planet, levels of carbon dioxide, and the movement of the tectonic plates—this is the first time that interstellar clouds have been considered a factor in ice ages.
Merav Opher, an astronomy professor at Boston University and fellow at Harvard Radcliffe Institute, said in a statement: "This paper is the first to quantitatively show there was an encounter between the sun and something outside of the Solar System that would have affected Earth's climate."
Our solar system is covered in a bubble called the heliosphere, which helps protect us from radiation and other damaging cosmic rays that would affect our DNA. This shield is made up of charged particles emitted from the sun, called the solar wind.
According to the researchers, an interstellar cloud may have shrunk the heliosphere to the point that Earth was left outside of it, leaving it exposed to the galaxy's radiation as well as particles that may have cooled the climate.
For the study, the team used computer modeling to look at where the Sun was positioned two million years ago.
Using data from the European Space Agency's Gaia Satellite, they also outlined the movement of the Local Ribbon of Cold Clouds system, a series of huge, dense, extremely cold clouds mostly made of hydrogen atoms.
One of these clouds—called the Local Lynx of Cold Cloud—may have come into contact with the heliosphere and collapsed it.
Without the protection of the heliosphere, Earth would have been exposed to the interstellar medium. This means our planet's atmosphere may have been affected by the combination of gas, dust and the atomic elements left behind by exploded stars, including iron and plutonium.
The researchers say this theory is supported by geological evidence that shows higher levels of the elements iron-60 and plutonium-244 isotopes in the ocean, on the moon, in the Antarctic snow, and within ice cores from the same time period.
These elements come from star explosions called supernovae and are found within interstellar clouds. Therefore, they were likely left on Earth while it was outside of the protective heliosphere.
The researchers believe Earth was outside the heliosphere for as long as 10,000 years.
"This cloud was indeed in our past, and if we crossed something that massive, we were exposed to the interstellar medium," Opher said.
The full findings of the study were published in Nature Astronomy.
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