Scientists are pushing to understand life’s chemical origins and potential development in cosmic environments, investigating scenarios like hydrothermal vents, meteorites, potential exotic life on Growing chemical gardens. Searching for life’s building blocks in meteorites. Sketching out a path to exotic life on a moon of Saturn.
Interplanetary probes and space telescopes take the search for life beyond Earth to new heights. But just as indispensable is the laboratory work on Earth itself. Experimenters seek to puzzle out the chemical origins of life, or capture evidence of molecules common to living things in samples from other objects in the solar system.
Darwinian Evolution in a Test Tube
Some even have kickstarted Darwinian evolution in a test tube. The process of natural selection, made famous by Charles Darwin, was seen in the well-known experiment, and appeared to meet, at least technically,
“My origin-of-life work is focused on how to get from a geochemical environment to the start of organic chemistry,” said Laurie Barge, co-leader of the Origins and Habitability Lab at NASA’s Jet Propulsion Laboratory in Southern California. “We don’t know what pieces of the first life came when. What came first? What came later? Was it before or after the cell emerged?”
Barge is known for chemical gardens – flasks full of materials that attempt to simulate the environment, chemistry, and even the electrical charge of hydrothermal vents on the floors of primordial oceans. They’re designed to explore how metabolism, a critical component of all life, might have chugged into operation in such vents some 4 billion years ago.
Astrobiological Theories and Hydrothermal Vents
Hydrothermal vents are just one of several scenarios astrobiologists have suggested as early paths to eventual life, and metabolism is not even life itself – just a way of turning organic compounds into energy, a baseline requirement for any living thing. The process later might have been co-opted by opportunistic, incipient life forms, though no one knows just how that could have happened.
These hydrothermal vents, or “chimneys,” also might be present on the sea floor of Saturn’s moon, Enceladus, or other “ocean worlds” that hide global oceans under shells of ice.
“These chimneys on the early Earth, also Enceladus: What types of environments, what sort of chemistry do those drive?” Barge asks. “What kind of energy do they generate?”
Whether the elements of eventual life began on a sea floor or, say, a pond on the land surface, they might have been infused with ingredients delivered from above.
Rocks as Time Travelers
While we can’t travel back in time to early Earth, many asteroids have remained unchanged for billions of years, making them akin to time capsules of the infant solar system. What’s more, pieces of space rocks that fall to Earth, called meteorites, also contain clues about the building blocks of early planets, and maybe even life.
At NASA’s Goddard Space Flight Center in Greenbelt, Maryland, Jason Dworkin, senior scientist for astrobiology, is investigating the composition and chemistry of meteorites.
Dworkin’s lab also analyzes samples of other solar system bodies returned to Earth by missions like Hayabusa2 from the Japanese space agency, Stardust, and Apollo, and soon-to-be-delivered asteroid samples from NASA’s OSIRIS-REx.
Organic compounds in rocks from space, though not signs of biology in themselves, might have been important to the origin of life on Earth – especially in the early period after Earth’s formation, when large asteroids were striking the surface more frequently.
“We try to understand the chemistry that could have been happening on Earth,” Dworkin said. “Though we know extraterrestrial material was raining down on Earth, we don’t know how important it was for life. We don’t know if it was a major or minor component, or the silver bullet that caused it to happen.”
Still, research by Dworkin and others has yielded potentially significant clues. In 2009, his lab was the first to detect an amino
The coming Artemis missions, taking humans back to the Moon, will include collection of samples by Artemis III; another planned “Sample Return” mission to
Titan’s surface is in such a deep freeze that water is essentially rock. Yet the moon has a thick atmosphere, lakes, rivers, and precipitation – the only solar system body other than Earth with such a liquid cycle.
The lakes and rivers are composed of methane and ethane. Could some form of life thrive on these liquids, as Earth life does on water?
Laboratory work has provided some surprising clues. Titan’s extremely low surface temperatures – minus 290 degrees
But experiments by researchers at
Evidence of exotic life forms thriving on methane or ethane, however, might be difficult to detect, even if they somehow developed on Titan’s surface.
“Once you get into ‘life as we don’t know it,’ there are a lot of open questions there,” Trainer said.
Yet Titan – like
How Life Began
While such findings can yield key insights, astrobiology in the lab is not limited to creation of potentially habitable conditions, exotic or otherwise. Other experiments explore pathways to the start of life itself.
Among the best-known of these was conducted by Gerald Joyce, a research professor at the Salk Institute in La Jolla, California, and collaborator Tracey Lincoln. They created an RNA-based system, then coaxed it into sustained Darwinian evolution in a test tube. Lincoln, lead author and Joyce’s PhD student at the time, published the finding in 2009.
Although it technically met NASA’s working definition of life – a self-sustaining chemical system capable of Darwinian evolution – Joyce says that in his view, it still didn’t qualify as a true life form.
“I was the first to say, ‘It doesn’t make it,’” Joyce said. Left to its own, the system, with its fragile, low-capacity RNA molecule, would hardly be able to evolve from where it started.
“It wouldn’t have been too long till it was dead,” he said. “There was just not enough information carrying capacity” in the relatively short strands of RNA that were used.
In Joyce’s view, life’s system for recording and transmitting information must, in itself, possess enough information capacity to evolve entirely new processes – body armor, locomotion, or reproductive strategies, for example.
“We’re talking about more than just being ‘capable’ of undergoing Darwinian evolution,” he said. “It has to have – this is where it gets hard – some broad capacity to undergo Darwinian evolution. You need enough information to keep evolving: sensory systems, nervous systems, things like
“Many exciting things are happening,” he said. “There’s a focus on extrasolar planets, but what is happening on Mars is also incredible, with rovers, a helicopter, and a sample-return mission coming. And the next target will be the icy outer moons. It’s a really fun time in astrobiology.”