Recipe for a planet: how life appeared on Earth
The origin of life on Earth remains a mystery to science in many ways. One of the key questions is related to how the chemical elements necessary for the emergence of the first organisms appeared on the young planet. The research, carried out with the support of NASA, offers a new look at the origin of phosphorus and nitrogen, as well as the role of Jupiter in the early history of the Solar system. For more information about how this can change the question of the origin of life, and how this is related to the modern volcanoes of Kamchatka, see the Izvestia article.
What scientists have actually discovered
When scientists try to understand how life appeared on Earth, they inevitably face the question of the origin of its chemical "building blocks". Where did the elements appear on the young planet, without which neither DNA, RNA, nor cells are impossible? Phosphorus and nitrogen are considered to be one of the most important among them.
A new study published in the journal Science Advances with the support of NASA offers an unexpected look at the history of these elements. Its authors concluded that a significant part of phosphorus and nitrogen could have reached Earth not from the outer regions of the Solar System, as previously assumed, but from the inner ones. Moreover, Jupiter probably played an important role in this process.
Today, the gas giant is located almost 780 million km from the Sun and seems far from earthly problems. However, 4.5 billion years ago, the Solar System was a rotating disk of gas, dust, and forming planets. During this period, Jupiter not only gained mass, but also influenced the movement of a huge number of substances around itself with its powerful gravitational influence.
The researchers analyzed the composition of ancient meteorites, a kind of "time capsules" that preserved information about the early stages of planet formation. They paid special attention to the ratio of phosphorus and nitrogen.
Comparing these data with the composition of the Earth's mantle, the authors concluded that it is not necessary to attract large amounts of matter from the outer regions of the Solar System to explain the observed concentrations. Bodies that formed closer to the Sun could have made a significant contribution.
What is the Earth made of?
For many years, much attention has been paid to the idea of space delivery of vital substances in research on the origin of life. It was believed that the young Earth could receive a significant part of the water, organic compounds and some biogenic elements due to bodies that arrived from the outer regions of the Solar system.
The new work does not completely negate this picture, but it does make it more complex. If the authors' conclusions are correct, then at least some of the phosphorus and nitrogen needed for the future biosphere could be of local origin, coming from bodies formed closer to the Sun and to the Earth's orbit. This means that the key chemical components of life could be much closer to the young planet than previously thought.
Such results are important not only for understanding the history of the Earth, but also for assessing the habitability of other planetary systems. In this case, elements can effectively form and accumulate near young rocky cosmic bodies, which expands the understanding of where in the universe it is worth looking for potentially habitable worlds.
However, according to Sergey Ipatov, Ph.D., a leading researcher at the GEOCHI RAS, this conclusion does not contradict existing ideas about the formation of the Earth.
— The probability of a collision with the Earth of bodies formed inside the orbit of Jupiter was significantly higher than the probability of a collision of bodies from the outer Solar system. Therefore, the contribution of internal bodies to the delivery of matter to Earth has long been considered significant," the scientist notes.
According to him, the main value of the new work lies not so much in revising the role of Jupiter, but in trying to explain why exactly this ratio of phosphorus and nitrogen is observed in the earth's mantle today. In this sense, the study helps to better understand how important the processes occurring in its immediate space environment could play in shaping the future habitability of the Earth.
Why do we need phosphorus?
Without phosphorus, life as we know it would simply be impossible. It consists of DNA and RNA molecules, it participates in the storage and transfer of energy inside cells, and is also a part of cell membranes. But the presence of an element and its availability for chemical reactions are not the same thing.
As explained by Alexander Mulkidzhanyan, Doctor of Biological Sciences, Professor of the Faculty of Bioengineering and Bioinformatics at Lomonosov Moscow State University, and Daria Dibrova, Candidate of Biological Sciences, Senior Researcher at the A.N. Belozersky Research Institute of the Lomonosov Moscow State University, today most of the phosphorus on Earth exists in the form of phosphates, phosphoric acid salts. They are poorly soluble in water and are not very willing to enter into chemical reactions. That is why modern agriculture depends on phosphorous fertilizers, and many ecosystems are deficient in this element.
This poses a serious problem for scientists studying the origin of life. Even if there is relatively little available phosphorus on modern Earth, it is not clear how the first RNA molecules could have formed more than 4 billion years ago.
— The task of finding a source of abundant, available phosphorus on ancient Earth is very non-trivial, so they usually "forget" about the need for phosphorus, — Izvestia's interlocutors note.
Most often, attention is focused on the search for water, organic substances, or energy sources, while the problem of available phosphorus is often perceived as secondary. Meanwhile, without solving this particular problem, many scenarios for the emergence of life turn out to be chemically unrealistic.
Back in the middle of the last century, scientists suggested that phosphorus could exist on the ancient anoxic Earth not only in the form of phosphates, but also in the form of more reduced compounds — phosphites. Such substances dissolve much better in water and are much easier to participate in chemical reactions necessary for the formation of complex organic molecules.
— RNA molecules consist of ribonucleotides connected to each other by phosphate groups. Such polymers could be formed spontaneously only if there were many phosphorous compounds capable of entering into chemical reactions, the researchers emphasize.
However, it is important for scientists not only to identify the source of these compounds, but also to understand in what form phosphorus existed on the early Earth and to what extent it was available for the chemical processes that eventually led to the emergence of the first living systems.
Could the Earth have created the conditions for life on its own
The debate about ancient meteorites and the role of Jupiter turns out to be only part of a much larger scientific task. Even if scientists pinpoint the source of phosphorus on the early Earth, they have yet to explain how this element became available for the chemistry of life.
Kudryavy Volcano on Iturup Island, Sakhalin Oblast
One of the possible solutions is proposed by Alexander Mulkidzhanyan, Daria Dibrova and their colleagues. According to their hypothesis, geothermal fields and intense volcanic activity could have played a key role in providing the early Earth with available phosphorus.
As an example, the researchers cite the Kudryavy volcano on the Kuril Islands. The temperature of its magma is significantly higher than that of most modern volcanoes, due to which volcanic steam is able to carry unusually large amounts of phosphorus and other elements necessary for life. The work of the group of geochemist Andrey Bychkov has shown that at high temperatures phosphorus is effectively removed from the bowels of the planet along with volcanic steam and can accumulate in the near-surface environment.
According to the researchers, such processes were widespread on the young Earth. After the giant collision that led to the formation of the Moon, the Earth's mantle remained significantly hotter than it is today for a long time. As a result, volcanic activity was much more intense, and conditions in many systems could resemble those currently observed only in the hottest fumaroles — cracks and holes in volcanic areas through which incandescent gases and steam escape to the surface.
"While the Earth's mantle remained superheated after the moon—forming impact, a very large amount of phosphorous compounds had to be brought to the surface with steam from all terrestrial volcanoes, ensuring their abundance on the Earth's surface," the scientists emphasize.
According to scientists, such a mechanism could supply the surface of the planet with chemically active phosphorus compounds for millions of years, creating favorable conditions for the processes that preceded the emergence of life.
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