Researchers at Yale University believe that life exists deep beneath the Earth's surface, not only changing what we know about life, but also how we might look for life on alien planets.

These researchers found proof of a bacteria living 12 miles underground, making it the first of its kind ever found. This also suggests that some life can exist at extreme conditions, meaning that similar life on other planets is possible.

Previously, the deepest life ever found was about 1 ½ miles below the Earth's surface. That means that these researchers have found proof of life deeper than we've ever seen before.

Although scientists suggested at this deep microbial life in the 1990s, it wasn't until recently that research followed up on the idea. The Yale team studied rocks on an island in northwestern Washington. The rocks had veins of aragonite that contained high levels of carbon, the kind of carbon associated with microbes that give off methane.

Researchers believe that the aragonite formed when the Earth's underground pressure and heat converted basalt rock into aragonite. Then, the underground microbes, which gave off methane, changed the carbon signatures of the rock, resulting in the readings the research team found when analyzing the island rock's isotopes.

The key factor here, though, is that these microbes sustained extreme heat underground with temperatures up to 250 degrees Fahrenheit, the hottest temperature we believe life can withstand. However, high pressure underground probably stabilized the microbe's DNA, so it survived there.

"We've seen over the past couple decades of exploration that life can survive in an incredible diversity of ecosystems, even in deep-sea vents and glacial ice," said Philippa Stoddard, an undergraduate in Yale University's geology and geophysics department. "If the deep earth was survivable for specialized microbes 100 million years ago, those same strategies could still work today."

So, if life can exist in such extreme conditions on Earth, it's likely that life similar to these microbes can sustain similar conditions on alien planets, such as Mars. Sure, Mars' surface is inhospitable to life, thanks to extreme temperatures and radiation, but that changes underground: life could very well exist there, protected from Mars' conditions.

"Underground environments would potentially be favorable locations for extraterrestrial life because they are more shielded from harmful surface conditions like cosmic radiation and insulated from extreme surface temperatures," said Stoddard. "It's definitely something we should keep in mind as we explore other planets."

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