One of the world’s greatest mysteries is how life on Earth began. Scientists have long sought to decipher where and how prebiotic molecules — those that preceded life — emerged. A new study suggests that the answers lie somewhere out in space, based on a recreation of the conditions in interstellar clouds that likely gave our planet a biological jumpstart.
The study, recently published in the Proceedings of the National Academy of Sciences, indicates that asteroid and comet impacts possibly supplied Earth with molecules essential for life-sustaining chemical reactions. It also signals that a better understanding of outer space chemistry could even hold implications for life elsewhere in the universe.
How Did Life Start on Earth?
Life arose on Earth somewhere between 3.5 billion years and 3.8 billion years ago, yet the circumstances that allowed this to happen have been subject to constant speculation. Scientists are concerned with how abiogenesis — the inception of life from non-living matter — could have occurred in the first place; some theories state that certain environments on Earth, like hydrothermal vents deep in the ocean or terrestrial hot springs, drove prebiotic processes.
The true catalyst for life, however, may have arrived from space. Despite the cold, icy conditions of interstellar clouds scattered between star systems, these regions contain a variety of prebiotic molecules.
Read More: New Hydrothermal Feature Emerges at Yellowstone National Park
Simulating Interstellar Space
Researchers involved with the new study were able to form complex carboxylic acids by simulating the conditions of interstellar space — these organic compounds are important components of metabolism, the process in living organisms that converts food into energy. They focused on molecules involved in the Krebs cycle, a series of reactions that cause cells to produce energy in nearly all living organisms.
To produce the prebiotic molecules, the researchers first froze simple gases to near absolute zero. The frozen gases were then exposed to “ubiquitous galactic cosmic ray proxies” and then slowly warmed to imitate the heating that happens as new stars form, according to a statement.
This method yielded organic acids associated with the Krebs cycle (including mono-, di-, and tricarboxylic acids), which have also been previously found on asteroids and meteorites. Samples from the asteroids Ryugu and Bennu, which were brought back to Earth, contained prebiotic molecules, for example.
“This work shows that the basic ingredients for life’s chemistry could have been made in space, long before Earth even formed,” said Ralf I. Kaiser, a chemist at the University of Hawai’i at Manoa, in a statement.
The Search for Prebiotic Molecules
The researchers say that prebiotic molecules from space dust and gas may have been carried to Earth by comets and asteroids.
Around 4 billion years ago, Earth went through a tumultuous period known as the “late heavy bombardment,” when severe comet and asteroid impacts made the planet too hot to support the existence of water and carbon-based life.
However, near the very end of this period, 3.8 billion years ago, life was able to form relatively quickly. This may have stemmed from less intense collisions that delivered prebiotic molecules to Earth after the late heavy bombardment subsided.
The search for evidence of extraterrestrial life has accelerated in recent years, and carbon-rich asteroids, known as C-type asteroids, are high on the list of sources to explore. NASA’s Lucy spacecraft has already embarked on a journey to meet multiple asteroids in space, set to fly by eight different ones over a 12-year period. The spacecraft will scan the surfaces of Trojan asteroids (which follow Jupiter’s orbit around the Sun) for organic compounds, which may provide further insight into prebiotic chemistry in space.
Read More: Basic Building Blocks of Life Found on Asteroid Bennu
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Jack Knudson is an assistant editor at Discover with a strong interest in environmental science and history. Before joining Discover in 2023, he studied journalism at the Scripps College of Communication at Ohio University and previously interned at Recycling Today magazine.
