Was Life Seeded from Space? ‘Complete Set’ of DNA Ingredients Discovered on Asteroid

"Organic molecules delivered from extraterrestrial materials may have played a key role in supplying building blocks for life on Earth,” said one scientist."

Scientists have discovered all five nucleobases—the fundamental components of DNA and RNA—in pristine samples from the asteroid Ryugu, according to a study published on Monday in Nature Astronomy. The finding strengthens the case that the ingredients for life are abundant in the solar system and may have found their way to Earth from space, according to a study published on Monday in Nature Astronomy. 

Life as we know it runs on DNA and RNA, which are built from five chemical bases: adenine, guanine, cytosine, thymine, and uracil. A team has now identified this “complete set” of nucleobases in rocks snatched from the surface of Ryugu in 2019 by the Japanese spacecraft Hayabusa-2, which successfully returned them to Earth the following year.

This discovery corroborates the results from another mission, NASA’s OSIRIS-REx, which returned samples of the asteroid Bennu that also contained all five nucleobases. Both asteroids belong to the same “carbonaceous” (C-type) family of primitive carbon-rich rocks, though the samples contain different ratios of the five nucleobases. 

"The finding strengthens the case that the ingredients for life are abundant in the solar system and may have found their way to Earth from space..."

Taken together, the findings shed light on the origin of life on Earth and raise new questions about the odds that it exists elsewhere. 

“These findings suggest that nucleobases may be widespread in carbonaceous asteroids and, by extension, in planetary systems,” said Toshiki Koga, a postdoctoral researcher at the Japan Agency for Marine-Earth Science and Technology (JAMSTEC), in an email to 404 Media. 

“This means that some of the key molecular ingredients for life could be commonly available,” he added. “However, this does not imply that life itself is widespread, but rather that the chemical starting materials for life may be more common than previously thought.”

The emergence of life on Earth, also known as abiogenesis, remains one of the biggest mysteries in science. To untangle this enigma, scientists first need to figure out how our planet was initially enriched with the basic stuff of life—including water, amino acids, and the nucleobases that make up our genetic material.

One popular hypothesis suggests that asteroids bearing these biological building blocks pelted Earth as it formed more than four billion years ago. This idea has been supported by the presence of nucleobases in pieces of carbonaceous asteroids that have fallen down to Earth, such as the Murchison meteorite of Australia or the Orgueil meteorite of France. 

Meteorites, however, are not pristine as they become eroded by exposure to space and can also be contaminated by terrestrial material after landing on Earth. To get cleaner samples, scientists launched several spacecraft to grab samples directly from the source, beginning with Japan’s Hayabusa mission, which delivered several milligrams of dusty grains from asteroid Itokawa to Earth in 2010. 

Hayabusa-2 and OSIRIS-REx then obtained even larger samples from their targets, bringing back 5.4 grams from Ryugu and 121.6 grams from Bennu. Previous studies have already identified more than a dozen amino acids associated with life in both samples, as well as evidence that these asteroids were once altered by ice and water. 

Now, following the discovery of all five nucleobases in the Bennu pebbles, Koga and his colleagues have found the complete set in Ryugu. The findings lend weight to the so-called “RNA world” model of abiogenesis. In this hypothesis, early life on Earth depended solely on RNA as a self-replicating molecule, laying the biological groundwork for later, more complicated systems that involved DNA and protein-based organisms. The extraterrestrial samples from Ryugu and Bennu provide evidence that at least some of the nucleobases that made up these early lifeforms came from outer space.

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Researchers Have Uncovered a Missing Piece in Life’s Origin Story

Deep beneath the ocean’s surface, mineral-rich hydrothermal vents may have hosted a critical chemical reaction that helped spark life on Earth.

Researchers at the University of Alberta report that they may have identified a missing piece in one of science’s biggest questions: how life first began on Earth.

Many scientists think life started deep on the ocean floor, near hydrothermal vents that release heat and mineral-rich fluids from beneath the crust. These environments could have supplied energy and raw materials for early chemistry. However, a major puzzle has remained. Without sunlight, how were essential nutrients, especially usable forms of carbon and nitrogen, produced in amounts sufficient to support the first living systems?

"Without sunlight, how were essential nutrients, especially usable forms of carbon and nitrogen, produced in amounts sufficient to support the first living systems?"

To investigate, Long Li and his colleagues in the Department of Earth and Atmospheric Sciences examined rock cores drilled about 200 meters into the oceanic crust in the South China Sea. Their analysis revealed signs of a process known as abiotic nitrogen reduction (ANR), in which minerals act as catalysts to convert nitrogen into chemically useful forms. The team concluded that this reaction likely generated nutrients needed for life to emerge.

One important product of this process is ammonium. Li explains that ammonium plays a central role in the abiotic synthesis of organic compounds, which are the molecular building blocks required for the development of the earliest life forms.

The study was conducted in partnership with researchers at the South China Institute of Oceanography and was published in Nature Communications.

Evidence from the Ocean Floor

“This definitely fills in the gap for the first-step reaction in the origin of life,” says Li. “People have searched for this reaction for a long time, but this is the first time we have convincing evidence to show it is occurring on Earth, and probably did occur on early Earth as well.”

"...minerals act as catalysts to convert nitrogen into chemically useful forms. The team concluded that this reaction likely generated nutrients needed for life to emerge."

Although ANR has been produced under controlled laboratory conditions, detecting it in natural ocean settings has been challenging.

According to the authors, modern biological activity alters nitrogen in seawater and sediments, making it difficult to separate abiotic signals from those created by living organisms. By studying deeply buried rock samples, the team was able to identify geochemical evidence consistent with a nonbiological nitrogen reduction process.

Implications for the Faint Young Sun Paradox

The findings may also help scientists address the “faint young sun paradox.” This long-standing problem asks how liquid water could have existed on early Earth when the young Sun emitted less energy. Climate models suggest that surface temperatures at the time should have been well below 0 C.

Despite those models, geological records show that liquid water was present at least 4.4 billion years ago. Li says this apparent contradiction can likely be explained by greenhouse gases such as carbon dioxide, methane, and ammonia, which would have trapped heat in the atmosphere. Hydrothermal vents on the seafloor may have helped generate these gases, contributing both to a warmer climate and to the chemistry needed for life.

Li adds that the strength of the evidence from the South China Sea suggests this reaction was not limited to a single location.

“We definitely need more evidence to show that. But since the conditions for ANR are common in both modern and ancient oceans, we reasonably speculate that this could happen globally over Earth’s history.”