A Cosmic 'Cold Cloud' May Have Enveloped Earth Long Ago, Shaping Human Evolution

Eric Mack Contributing Editor
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Eric Mack
2 min read
Supernova explosion as imagined by an artist

An illustration of a supernova explosion. Such blasts produce damaging galactic rays that may have altered Earth's climate 2 million years ago. 


What's happening

A new theory suggests Earth may have been exposed to climate-altering radiation 2 million years ago.

Why it matters

If the theory's true, the major change in space weather might have influenced the course of human evolution.

A controversial astronomer has co-authored a new research paper that suggests our solar system may have passed through a massive cloud of cold interstellar gas 2 million years ago, which could have altered the emergence of our species. 

Boston University astronomy professor Merav Opher led the work, along with Harvard's Abraham Loeb, who's best known for pushing the idea that the odd interstellar object 'Oumuamua was most likely some sort of alien probe. Loeb's theory, which he outlined in a book last year, has been roundly criticized by a number of other astronomers. 

Opher and Loeb have put out a pre-print draft of a paper explaining how our planet may have endured a period when it was essentially exposed to galactic cosmic rays, which are a form of damaging radiation that largely originate from supernova explosions. Normally, the solar wind from our sun creates the heliosphere, a sort of protective bubble around the solar system, particularly the inner planets, that reduces our exposure to such nastiness from interstellar space. 

The two veteran scientists use geological samples and computer simulations to explore the possibility that a large mass of cold gas swooped through our corner of the cosmos right around the time that our ancestors like Homo habilis were starting to use stone tools. 

This cold cloud could have shrunk the heliosphere's protective cocoon to a size much smaller than Earth's orbit, leaving our world in direct contact with the interstellar medium.

It's important to note that this paper has yet to be peer reviewed and should be treated as nothing more than a theory from a few heavyweights in the field, including one with a tarnished reputation in the eyes of some. That said, it's an interesting theory.

"If this really happened, it would have altered space weather, terrestrial climate, and possibly even human evolution," another astronomer, Tony Phillips, writes at Spaceweather.com.

The time period in question was one of increased variability in Earth's climate. In particular, evidence points to an increasingly arid environment in Africa at the time. The changes forced our forebears to move to the north, and they evolved during those generations to become what we know today as Homo sapiens.

Opher and Loeb think the huge macro event that triggered this chain actually took place in space.

"We postulate that the encounter of the heliosphere with the cold cloud triggering the climate change was a critical component of the human evolution as a result of geographical migration," the paper reads.

So it's possible that dramatic space weather made us who we are today and that we're probably the better for it, but it's likely not something we'd want to go through again anytime soon, as evolution can come at a steep price. 

For their part, Opher and Loeb are calling for their hypothesis to "be investigated with detailed climate models."