How does life form — and then, survive and thrive? Astronomers have sought answers to that question for decades, but they have only gathered small pieces of the cosmic puzzle. To understand how life formed on our own planet, they argue, we must look to the universe for answers.
As we search for life on different planets, we have had to come to terms with the reality that life on other planets may not look exactly like life here on Earth. Should it exist, life on Mars, Enceladus, or a far-flung exoplanet may thrive under very different conditions to our own.
A new study suggests that microbial life could possibly survive on hydrogen alone, not needing what many scientists had believed to be a basic requirement for life: sunlight.
The study was published Monday in the journal Proceedings of the National Academy of Sciences.
When it comes to finding life on other planets, astronomers only have the Earth to serve as an analog for a world that hosts living organisms.
Therefore, when looking for what conditions are suitable for life to survive, they base it on a few elements that are considered essential to life on Earth.
In order for life to form, a planet would need water, an atmosphere, a source of energy, and most importantly, the right amount of heat, radiation and light coming from its host star.
Our Solar System owes whatever habitability it has in part to the Sun’s disposition.
But the researchers behind the new study suggest that life on other planets may not need sunlight to form and survive. Instead, their research shows life may survive on hydrogen alone.
To come to this conclusion, they measured the concentration of hydrogen in the meltwater from a glacier in Southern Iceland. They found that as the meltwater passed over basalt rock, there appeared to be higher concentrations of hydrogen than in meltwater which had passed over carbon-based rock.
As water interacts with mineral surfaces, which is what happens when glaciers touch the surface of Earth's bedrock, it appears to generate the chemical resources microbial life can use as the energy they need to survive and thrive on, according to the study.
Therefore, even when deprived of sunlight, microbial life can find another way to survive.
Curiously, the metabolic pathways seen in these microbes reflect life found in another extreme — although in a totally different sense — environment. They share the same characteristics as bacteria living in very hot or very acidic environments, like the thermophilic bacteria living in the Grand Prismatic Spring in Yellowstone National Park, for example.
These extreme forms of life and the seemingly hostile places they colonize spur astronomers' search for life elsewhere in the universe. Ever since the 1992 discovery of the first exoplanet orbiting around a star that's not the Sun, astronomers have found hints that extraterrestrial life could thrive somewhere else.
So far, scientists have found more than 4,000 exoplanets. A handful exist in the so-called 'Goldilocks zone' — the region of space between a star and a planet supposedly ideal for life to spring forth. Closer to home, in our own Solar System, scientists have discovered signs of phosphine in the clouds of Venus — a small hint of a biological chemistry down below. On Mars, scientists have found water — one of the key ingredients of life, like sunlight — suggesting the planet may once have harbored life.
But these are mere hints. Our search for life on these planets has not been successful... yet.
The scientists behind the new study believe that if life can thrive in the Icelandic glaciers, then similar environments on icy exoplanets may also be capable of supporting life. Soon, NASA plans to launch Dragonfly — a small, helicopter-like craft that will scan Titan's atmosphere for signs of life. Titan is the largest of Saturn's moons, and experiences freezing surface temperatures of -290 degrees Fahrenheit. Scheduled to launch in 2026, Dragonfly will look for biosignatures — features that could only have been produced as a result of life — encased in Titan's ice.
Abstract: Life in environments devoid of photosynthesis, such as on early Earth or in contemporary dark subsurface ecosystems, is supported by chemical energy. How, when, and where chemical nutrients released from the geosphere fuel chemosynthetic biospheres is fundamental to understanding the distribution and diversity of life, both today and in the geologic past. Hydrogen (H2) is a potent reductant that can be generated when water interacts with reactive components of mineral surfaces such as silicate radicals and ferrous iron. Such reactive mineral surfaces are continually generated by physical comminution of bedrock by glaciers. Here, we show that dissolved H2 concentrations in meltwaters from an iron and silicate mineral-rich basaltic glacial catchment were an order of magnitude higher than those from a carbonate-dominated catchment. Consistent with higher H2 abundance, sediment microbial communities from the basaltic catchment exhibited significantly shorter lag times and faster rates of net H2 oxidation and dark carbon dioxide (CO2) fixation than those from the carbonate catchment, indicating adaptation to use H2 as a reductant in basaltic catchments. An enrichment culture of basaltic sediments provided with H2, CO2, and ferric iron produced a chemolithoautotrophic population related to Rhodoferax ferrireducens with a metabolism previously thought to be restricted to (hyper) thermophiles and acidophiles. These findings point to the importance of physical and chemical weathering processes in generating nutrients that support chemosynthetic primary production. Furthermore, they show that differences in bedrock mineral composition can influence the supplies of nutrients like H2 and, in turn, the diversity, abundance, and activity of microbial inhabitants