How Does Life Start? Meteorites Have Brought Ingredients of DNA to Earth

It’s not easy to catch a shooting star, so scientists try to make the most out of every meteorite they can find, peering inside to try to learn its secrets. For some scientists, the ultimate secret would be signs of alien life tucked away inside the lump of rock—and they’re better able to look for those signs than ever before.

The idea that meteorites could have shuttled—or even still be shuttling today—life across or between solar systems is called panspermia. It’s a controversial  idea among scientists. “A lot of people are still struggling to convince other people that it could be feasible,” Queenie Chan, a planetary scientist at Open University in the U.K., told Newsweek.

Scientists have even looked for visible traces of living creatures inside meteorites, like the infamous Martian meteorite discovered in 1984 and known as Allan Hills 84001, which some scientists argued contains the fossilized worm-like remains of extraterrestrial creatures. But later research showed that the magnetite crystals Martian-lovers had argued could only be created by living things could be produced by a natural geological process. And now scientists have new ways to look for panspermia’s microscopic fingerprints even in meteorites that fell decades ago.

“All this time, we were just waiting for the technology to be available for this organic analysis.” Chan said. For example, she recently used her background in organic chemistry to analyze with colleagues little pockets of liquid found locked into salt crystals buried deep inside two meteorites, called Zag and Monahans, that fell to Earth in 1998. That research found a trio of particularly intriguing types of compounds: water, amino acids and large clumps of carbon, oxygen and nitrogen.

“They’re bringing little bags of organic ingredients onto the Earth’s surface,” she added, where they can undergo a range of chemical reactions that could theoretically lead to living things. Of course, in order to do that, they have to survive the journey to Earth, which is never a smooth ride.

01_24_meteorite_analysis Are meteorites tiny space transports? Martin Bernetti/AFP/Getty Images

There’s the physical shock created by slamming into Earth’s atmosphere, plus the huge amount of radiation and heat that comes with the journey. But Chan says that if a meteorite is large enough, there’s plenty of rock to shield life or its ingredients from those deadly conditions.

The outside of meteorites can reach temperatures as high as 1800 degrees Fahrenheit—that’s how you recognize meteorites, it turns out, you look for a round, dark rock that, when opened, reveals that only the outermost fraction of an inch is actually black. That’s what scientists call the fusion crust: "It is basically molten rock on the outside that go cooled really quickly." The crust is a dead zone, completely sterilized by the scalding temperatures.

But with a little luck, there’s plenty of space inside buffered from those extreme conditions. "It's like a little cradle inside of the rock," Chan said—a cradle that, as she found from her analysis of salt crystals buried within a meteorite, can protect compounds that make life happen.

Read more: Ancient Meteorites That Crashed to Earth Carried Ingredients for Life, Including Water and Organic Compounds

The fiery entry isn’t the only time life within a meteorite could be vulnerable to toasty temperatures, she added. Modern technology can show whether the stuff inside a meteorite was heated as it formed, thanks to small structural differences in compounds. High temperatures usually kill life, so scientists like Chan hope for samples without this heat signature.

And as to what types of molecules they want to find, Chan says the gold standard would be amino acids, the building blocks of proteins—specifically, amino acids that are all the left-handed flavor, which matches what life here on Earth uses. Her work has found amino acids, but not displaying this characteristic, as well as the "letters" that make up DNA and large molecular clumps of carbon and hydrogen.

For now, Chan and her colleagues are still watching and waiting, using whatever tools they can to study meteorites. “If somebody finds life, that would be phenomenal.”