Nitrogen is one of the main components of amino acids, which are the basis of RNA and DNA. Therefore, life as we know it could not have arisen on Earth without this element. The problem is that during our planet’s formation, there was relatively little nitrogen around it. Scientists know of nitrogen compounds that can maintain stability under conditions in the interior of the Solar System. Unfortunately, such compounds have not yet been found either in the nearest interplanetary dust or in micrometeorites formed nearby.

On the other hand, objects formed far from the Sun contain plenty of nitrogen. For example, in the form of ammonium salts. And this is confirmed by observations of comets and icy bodies in the outer regions of the system. So how did this nitrogen reach the edge of the Earth? Scientists performing isotopic analysis of lunar rock samples had previously discovered that the “external” source of nitrogen is asteroid micrometeoroids flying to us. To estimate their contribution to the world’s nitrogen reserves, it is necessary to know the content of this element in their composition, and such calculations have not been made. Ryugu asteroid samples were helpful.

Ryugu is an ordinary near-Earth asteroid belonging to spectral class C. In 2019, the Hayabusa-2 probe collected rock samples from its surface and delivered them to Earth. In an article published in the Journal Nature AstronomyAn international group of scientists has presented a new analysis of these samples. According to the results, micrometeorites from the outer regions of the Solar System became abundant sources of nitrogen for the young Earth. Moreover, the volumes of available nitrogen were previously greatly underestimated.

The solution lies in the cosmic weather conditions of asteroid surfaces. Under the influence of solar wind particles and micrometeorites, chemical reactions occur in the rock, during which a stable nitrogen – iron nitride compound is formed. One of the main minerals in Ryugu samples is magnetite. Under the influence of hydrogen ions from the solar wind and due to the heat of collision with micrometeorite particles, magnetite loses oxygen atoms. Thus, pure iron remains on the surface of magnetite granules, which turns into iron nitride, which binds nitrogen in chemical reactions with ammonium from micrometeorites.

There are many Ryugu-like objects in the inner solar system. Therefore, access to nitrogen on the young Earth was much higher than scientists thought.

But the problems with nitrogen availability don’t end there. On the young Earth, as it is today, most of the nitrogen was in the form of the low-activity N molecule.₂. Very few modern creatures have the ability to use it in this form. Therefore, the question of how nitrogen was “digested” by the first life forms remains open.