‘The evolution of prebiotics’: Why a molecule brought from space could explain the mystery of life on Earth

Madrid. – A team of Japanese scientists has announced a discovery that may help explain one of the biggest questions in science.How did life arise on Earth?

The answer, according to them, should be found in The oldest material ever reached from the solar systemHayabusa 2: About five grams of soil was removed from the surface of the space probe Ryugu. This asteroid is a black ball about 900 meters in diameter that orbits between Mars and Earth With a minimum mileage of approximately 100,000 km. To scientists, it’s like a time capsule that’s been wandering around and untouched since the birth of the solar system, 4.5 billion years ago. Its composition reveals how it is the oldest and most important material from which all planets, including Earth, were subsequently formed.

In December 2014, Japan launched the Hayabusa 2 probe., which was to become the first human spacecraft capable of visiting an asteroid, extracting samples from it, and returning it to Earth. Its predecessor, Hayabusa 1, had already done something similar, but there was very little land to be torn apart by the Itokawa asteroid. Upon reaching Ryugu, Hayabusa 2 not only collected dirt from the surface, but also fired projectiles at Ryugu, exposing its entrails and sampling the interior.

In December 2020, an armored capsule escapes re-entry and crashes in a remote desert spot in South Australia. It was the samples sent by Hayabusa 2. After a while, the researchers confirmed this The ship had found a 5.4g native asteroid. It was the oldest and purest material that humanity had access to.

The scientists took that soil and dissolved it in superheated water, looking for organic molecules. The most recent results are published in Nature Communicationsshow it Ryugu contains uracil, one of the four genetic letters that make up RNA.. It is believed that this complementary DNA molecule, although simpler, could be The first form of life on Earth.

“The presence of uracil in Ryugu is definitive evidence of the presence of this compound in extraterrestrial matter,” explains Yasuhiro Ohba, a biochemist at Hokkaido University and first author of the study. [que compone asteroides y otros cuerpos]He says: “This discovery reinforces The hypothesis that organic molecules found in meteorites, asteroids, and comets contributed to the evolution of Earth’s organisms Early and possibly the origin of life on this planet.

Earth was formed 4.5 billion years ago Made of dust and rocks that accumulated around the sun. Materials that the giant planets, such as Jupiter and Saturn, did not use, were left available to form the four rocky planets: Mars, Venus, Mercury and Earth.

About 4.1 billion years ago, the young Earth was heavily bombarded by comets and asteroids. Much of today’s ocean water as well as essential organic compounds could have arrived on board these bodies. The first forms of life, microbes that already have the ability to reproduce, already existed about 3.7 billion years ago. Although no one knows how it arose, it is possible that the DNA and RNA that allowed it to reproduce and develop was formed in an environment with heat, water, etc. Perhaps the building blocks of life are from spaceLike hydrothermal vents on the ocean floor.

The Japanese scientists associated with Hayabusa 2, also from the Japanese Space Agency Other organic compounds, such as nicotinic acid, are foundFound in Vitamin B3. On our planet, this molecule helps organisms extract energy from nutrients, create cholesterol and fat stores, and form and maintain DNA.

Ohba points out that this is the first time that uracil has been found on an asteroid. One of the most interesting results is this Samples from the asteroid’s interior contain more uracil than those on the surface, and are more battered by radiation and exposure to a vacuum. This confirms the view of the asteroids as boxes protecting the material intact from the origins of the solar system.

The finding joins findings from other teams, which have previously found uracil in meteorites. Fragments of asteroids that escape entering Earth’s atmosphere and fall to its surface. The rest of the “letters” that make up RNA and DNA are also found in meteorites: adenine (A), cytosine (C), guanine (G) and thymine (T). In previous studies, Hayabusa’s team had already reported that in Ryugu there are also amino acids, which are the building blocks for creating proteins from information stored in DNA. The amino acids in that body were certainly strange, because they were not among the twenty that terrestrial organisms use to make the proteins that keep them alive.

It is quite a scientific and sterile feat to have been able to take samples millions of kilometers from Earth, bring them back and analyze them in different laboratories, both in Japan and the United States, without them ever being contaminated.which is a problem often found with surface meteorites.

Julie Perito, an expert in synthetic biology at the University of Valencia, highlights that “it is a very good study from a technical point of view. What shows us is that the oldest asteroids already contain the bricks and mortar of life, although there are no constructions yet, such as walls,” as he embodies .

The uracil found in Ryugu is composed of four carbon atoms, four hydrogens, two nitrogens and two oxygens (C4H4N202).. In nature, uracil does not go alone, but must attach to a sugar molecule called ribose, which contains five carbon atoms, five oxygen, and ten hydrogen, as well as three phosphate molecules, with four hydrogen, one phosphorus, and four oxygen. And to all this would be added other RNA letters, with many sugars and phosphorous compounds attached to them, a level of biochemical complexity never found in asteroids, meteorites or comets. However, we will be light years away from the dimensions of the simplest single-celled organisms, which can be similar to those that first appeared on Earth about 4 billion years ago.

A small genome of free-living bacteria can have up to a million monomers [letras de ADN]The total number of atoms will be about 40 million, Perito explains. ” According to the expert, this is the main dilemma of life. On Earth, four genetic letters are enough to form DNA, and hardly 20 amino acids to form DNA. 200 million different proteins that allow all living things on the planet to live.

A great variety of basic compounds can be formed in space, but only on Earth was the enormous complexity necessary to form living organisms possible.; First, single-celled microbes and, long after, an entire explosion of organisms divided into three large domains: bacteria, archaea, and eukaryotes, the type of organisms made of complex cells with a nucleus to store their own DNA that includes humans, animals, plants, and mushrooms. The other great mystery of the evolution of life is that size doesn’t matter: There are amoebas whose genome is 100 times larger than that of a human, even though both are built with variations and repeats of the same four genetic letters.

Ester Lázaro, a researcher at the Center for Astrobiology (CAB) in Madrid, believes that these new tests “add and reinforce what we already had in mind”, referring to the fact that the building blocks of life can reach the planet through asteroids and comets.

Martha RuizThe researcher in prebiotic chemistry at CAB explains: “The identified compounds are interesting both from the point of view of prebiotic chemistry and from chemical evolution hypotheses that try to explain the emergence of life on Earth from a sample group of organic molecules, that originated from our planet or that they traveled to and transported in meteorites and asteroids, which were able to self-assemble, self-organize and eventually generate protocells.” “Uracil – highlights – is part of current nucleic acids (RNA and DNA); imidazoles, also found in Ryugu, can act as catalysts for the activation of nucleotides, amino acids as amplifying agents, and nicotinic acid is part of current cellular metabolism as part of some Coenzymes.

Next September, another space capsule will pass through the atmosphere. He will open his parachute and land softly somewhere in the desert of Great Salt Lake in Utah, United States. This will be NASA’s first attempt to emulate Japan’s feat. If all goes well, Inside the box will be the original soil samples from Bennu, a 490-meter-diameter asteroid that fell into near-Earth orbit. by the gravitational pull of the giant planets.

According to NASA, the risk of hitting Earth is zero for at least the next century, but the agency sent the mission there. Osiris Rex to collect samples. Japan’s Ohba will be part of the team that analyzes this material, determines its age, and possibly finds organic compounds that shed more light on how it all began.

By Nuno Dominguez

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