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Solar System's Run-In With 'Space Cloud' May Have Triggered a Series of Ice Ages 2 Million Years Ago, Says Scientists

Computational models suggest that two million years ago, solar winds ran into a space cloud.

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Germany, Mecklenburg-Western Pomerania, Rügen, Sassnitz, Mole in winter. (Representative Cover Image Source: Getty Image | Photo by Westend61)

Around two million years ago, Earth underwent a series of temperature fluctuations, facilitating several ice ages. Many reasons have been speculated for this bewildering phenomenon. These changes had a major impact on the existing ecosystems of those times. A team of researchers has now come up with a reason rooted in space for the phenomenon. They believe a huge interstellar cloud's interaction with the solar system, possibly caused the havoc. Their reasoning was explained in detail within the journal Nature Astronomy. This investigation was aided by readings collected from the European Space Agency's (ESA) Gaia satellite.

Pleiades Cluster "Seven Sisters", taken with a Canon EOS 4000D and M45 200mm ff 60x30s @3200 ISO LE process (Representative Image Source: Wikimedia Commons | Photo by Giuseppe Donatiello)

A Series of Ice Ages

Around two million years ago, human ancestors cohabited on Earth with saber-toothed tigers, giant sloths, and mastodons, according to Smithsonian Magazine. This picture underwent a massive transformation when a series of ice ages befell the planet. Until 12,000 years ago, sea levels rose and fell as well as glaciers froze and melted, due to temperatures constantly fluctuating from one extreme to another.

The creatures had to adapt quickly to survive, with many failing in this pursuit and vanishing permanently from the planet. A big shift that occurred during this period was plant and animal life moving towards the equator, where it was warmer compared to the poles. For long, researchers have cited varying causes, like volcanic eruptions, carbon dioxide levels in the atmosphere, and Earth's tilt, as reasons. Another reason has now entered the party from outside the Earth.

Zoom-in of the LxCCs as seen in 21 cm data from the GALFA-HI survey (Image Source: Nature Astronomy)

Giant Interstellar Cloud

Researchers claim that two million years ago, the solar system likely came across a dense patch of interstellar gas and dust, traveling through the Milky Way, according to Space. This patch was supposedly so thick that it could hinder "solar wind," a stream of charged particles coming from the Sun and hitting Earth. The cloud essentially interfered with this system, and the changing levels of solar wind reaching Earth resulted in fluctuating temperatures. Though such an encounter has been speculated previously, this is the first time a team of experts has been able to come up with findings, showcasing that the interaction could have interfered with solar wind.

The entire solar system is enveloped by the heliosphere, a giant bubble made out of plasma from the Sun. This shield protects Earth from harmful things, like radiation and galactic rays, which can negatively impact the DNA of living beings. The bubble gets facilitated when solar wind clashes with the interstellar medium, the substance present between stars in the Milky Way Galaxy. The bubble is rejuvenated constantly by a steady flow of solar wind. Researchers believe that the cloud's interference led to the heliosphere's compression, which reduced the protection offered by the shield, allowing it to become vulnerable to radioactive particles. These particles then possibly caused the havoc that entrapped Earth for more than a million years.

Investigation of Researchers

Experts essentially created computer models that allowed them to look into the solar system's past, according to Boston University. Through the models, the team understood the likely position of the Sun two million years ago and the then state of the heliosphere. They also managed to map the past trajectory of the Local Ribbon of Cold Clouds system, a collection of massive and dense cold clouds, composed of hydrogen atoms, that traveled through the Milky Way. The simulations indicated that one of the clouds in the system, Local Lynx of Cold Cloud, may have been the one involved in the fatal interaction, which weakened the heliosphere.

The collision between the LxCCs and the Sun is shown in the LSR frame using an interactive graphic (Image Source: Nature Astronomy)

The findings were backed by geological evidence showing an elevation of 60Fe (iron 60) and 244Pu (plutonium 244) isotopes in the ocean, Antarctic snow, and ice cores. This elevation could be explained by Earth becoming exposed to radioactive particles from the interstellar medium, typically filtered by a strong heliosphere. Researchers also found that the timing of the clash and the cooling of the planet also aligned.

"Only rarely does our cosmic neighborhood beyond the solar system affect life on Earth," said Avi Loeb, director of Harvard University's Institute for Theory and Computation and coauthor on the paper. "It is exciting to discover that our passage through dense clouds a few million years ago could have exposed the Earth to a much larger flux of cosmic rays and hydrogen atoms. Our results open a new window into the relationship between the evolution of life on Earth and our cosmic neighborhood."

Researchers believe that the situation turned to normal after the Earth moved away from the cloud. The team is now looking forward to knowing more about this interaction, because the space is filled with such clouds, and a similar clash cannot be ruled out completely in the future. If experts have an understanding of this phenomenon's effects, it could help humanity be more prepared for its consequences compared to our ancestors.