Was Mars habitable for life? A new study brings us closer to the answer

This discovery changes much of what we knew about the Red Planet, and opens the door wide to the possibility that life may have originated on it in ancient times.

A 50 year old mystery

For more than fifty years, scientists have been chasing one question: Was Mars habitable in the past? This simple question was the motivation behind dozens of space missions sent to explore the Red Planet.

Each new mission brings us one step closer to the answer, and the latest study adds an important piece to this puzzling puzzle.

The Nocian era: the decisive period

Mars is about 4.5 billion years old, similar to the age of Earth, and its history is divided into different geological eras. The new study highlights a crucial period known as the “Noachian epoch,” which extends from about 4.1 to 3.7 billion years ago, that is, a time when life was still forming on Earth.

This period was one of the most violent periods in the history of the solar system, as the planets were subjected to an intense barrage of giant meteorites in an event known as “delayed heavy bombardment.” The effects of these violent collisions are still evident on the surface of Mars today, most notably the huge Hellas and Argyre basins, each of which can accommodate the waters of the entire Mediterranean Sea, and there is still room in it.

Surprise: Violence created life?

At first glance, one might think that this turbulent period was very harsh and not suitable for the emergence of life. But surprisingly, scientific evidence indicates exactly the opposite. In this particular era, and in the midst of this cosmic violence, it seems that Mars was the most susceptible to the emergence of life.

Evidence of this is found in the planet’s topography, such as dry river valleys that penetrate the surface, ancient lake beds, and fossilized beaches and river deltas. All of these geological formations could only be formed by the presence of water flowing on the surface for long periods of time.

The scientific debate about the climate of Mars in the Nahiyah era is still raging, and there are two main theories:

• The first theory: Mars was cold and frozen, with large amounts of ice melting intermittently as a result of meteorite impacts or volcanic eruptions.
• Theory 2: Mars was warm, humid, and mostly ice-free.

The problem is that the sun billions of years ago was about 30% less bright than it is today, which means less heat reached Mars. For Mars to be warm, it needed a very dense atmosphere full of greenhouse gases like carbon dioxide.

But the irony is that when carbon dioxide exceeds a certain limit, it turns into clouds that reduce the greenhouse effect instead of increasing it. For this reason, the “cold Mars” theory seemed more plausible to many.

The probe that settled the controversy

In February 2021, the Perseverance probe landed on Mars on a historic mission. Scientists chose the “Lake Jezero” area specifically because it contained an ancient lake. Images taken from orbit showed rocky terraces in the shape of fans, formed by the flow of water through the walls of the crater, with deposits rich in clay minerals.

The new study analyzed samples of clay grains called “kaolinite” found inside one of the ancient flow channels. These grains bear clear signs of being subjected to severe weathering and chemical alteration by water during the Nocian era.

What is really interesting is the chemical composition of these grains: they are severely lacking in iron and magnesium, but rich in titanium and aluminium. This means that these rocks were not changed by hot water resulting from the melting of ice with lava or meteorites (which is what would have happened if the cold theory were correct), but rather they changed under moderate temperatures and heavy and continuous rain.

A striking resemblance to Earth

Scientists found a clear similarity between the chemical composition of these grains and similar clay on Earth dating back to periods when the climate was warmer and more humid. Scientists conclude that these grains were formed under heavy rains similar to the ancient climate of Earth, and that they likely represent the wettest periods on Mars, and perhaps the most suitable for the emergence of life.

Most importantly, these conditions continued for long periods, perhaps thousands or even millions of years, which is sufficient for life to arise and develop if the conditions were appropriate.

This is not the first time that the Perseverance probe has raised controversy. Last year, the scientific team announced the discovery of potential biosignatures in other samples it collected from the same area. These precious samples were carefully stored in sealed containers on the probe, awaiting a future mission that would return them to Earth.

But the problem is that NASA temporarily canceled this mission, which means that the samples will not reach Earth laboratories for many years to come. We will not know for sure whether it contains real traces of ancient Martian life until we study it in terrestrial laboratories.

The decisive test for these samples will be the so-called “Noll Criterion”, a strict rule developed by astrobiologist Andrew Noll, which states that in order for something to be considered evidence of the presence of life, it must not be explainable by chemical and geological processes alone, but rather it must be impossible to explain without the presence of life.

Source: Independent