Geologists have identified intelligent life as a natural outcome of planetary evolution.

The solar system has existed for 4.6 billion years. If we consider the emergence of written language as the starting point for intelligent civilization in this system, humanity has only been around for about five thousand years. Even if we take the first use of tools by human ancestors as the starting point, the age of earthly civilization is still insignificant by cosmic standards—2.6 million years.

According to forecasts, the Sun will continue its thermonuclear "life" for another five billion years, but modern science suggests that it will become increasingly intense over time, and in just one to two billion years, Earth may become too hot not only for humans but possibly for life in general. This raises the question among scientists: why did we, as an intelligent community, appear "under the curtain," when we have relatively little time left?

British physicist Brandon Carter proposed the "difficult steps" hypothesis in 1983: he believed that evolution as a whole is too slow, and it often requires more time to create intelligent beings than a star can provide. According to Carter, Earth was simply fortunate to pass through difficult "intermediate stages." Among these, he identified the emergence of DNA and the separation of human ancestors from primates.

This line of thought resonates with other well-known concepts. First, there is the Drake equation—a formula proposed by Frank Drake in 1961 to estimate the expected number of intelligent civilizations specifically in our Milky Way galaxy. This equation contains many unknowns, leading to various interpretations. Advocates of human exceptionalism refer to the rarity of Earth-like planets and the improbability of the necessary evolutionary circumstances for the emergence of intelligent beings.

It is also worth mentioning the Great Filter theory, which looks even further ahead: it addresses the obstacles that prevent an intelligent civilization not only from arising but also from developing to a stage where it can be detected in the vast cosmos, meaning it could be discovered by other civilizations.

In a recent article for the journal Science Advances, researchers from the USA and Germany examined Brandon Carter's theory and explained that he reasoned as an astrophysicist, but they propose to view the issue from a geological perspective. The authors of the article suggested that we are not "late" because evolution itself takes so long, but rather because of specific characteristics that have shaped Earth.

The researchers emphasized that initially, Earth was unsuitable not only for the emergence of intelligent life but for any life at all, except for the most primitive single-celled organisms. Everything changed with the Great Oxygenation Event, also known as the oxygen catastrophe, because the emergence of oxygen was lethal for most of the life that existed at that time. Only those who adapted to utilize it survived. However, evolutionarily, oxygen turned out to be a gift, as it opened up possibilities for much greater biological diversity. If this had not occurred, we would not be here.

The "culprits" of this epochal event are considered to be microscopic blue-green algae—cyanobacteria—since they were the first known oxygen producers. This revolution is estimated to have occurred around 2.4–2.2 billion years ago. Thus, Earth "lived" for billions of years before conditions were created for the eventual emergence of humans. This means that if we count from that moment, it took just over two billion years for intelligent life to evolve from microscopic forms.

The researchers believe that on some other Earth-like "comfortable" planet, no oxygen catastrophe may occur at all, but it is also quite possible that some analogs of cyanobacteria could appear much earlier. By the time we still had a kingdom of sponges and jellyfish on Earth, beings on another planet might already be building cities, telescopes, and spaceships.

This brings to mind the famous "Fermi Paradox"—the question of where extraterrestrial civilizations are and why we do not find them. However, many astronomers assure us that it is still too early to speak of humanity's solitude—we still see and "hear" very little in the cosmos. In any case, the idea of faster evolution on other planets will remain merely a hypothesis until we discover at least one such case.