Chemical analysis of certain rocks ancient sedimentary rocks in various parts of the world, carried out by an international research team, led by a researcher from the Petrographic and Geochemical Research Center, has allowed us to obtain the oldest data that we currently have on the earth's atmosphere.
These results reveal that more than 4.000 million years, the composition of the Earth's atmosphere was very similar to that which existed a billion years later, when a microbial biosphere developed on the planet's surface, being the origin of the diversity of life that we know today.
The importance of the atmosphere in the development of life
This finding, recently published in the journal PNAS, could provide a clearer understanding of the early processes that led to the emergence of Life on earthUntil recently, scientists had only very limited and diverse computer models of the early characteristics of the atmosphere. Now, this research offers key data that can help confirm or refute some of the most widely accepted theories about the origin of life on our planet.
Preliminary study on the primitive atmosphere
This new analysis builds on a previous study conducted in 2008, which found that rocks on the coast of the Hudson Bay, in northern Quebec, were deposited in the form of sediments more than 4.300 billion years ago, a few hundred million years after the formation of the Earth.
In fact, researchers have found that the atmosphere may not have had a significant amount of molecular oxygen (O2) during that period. Free oxygen only began to accumulate billions of years later, as a result of oxygenic photosynthesis by organisms such as cyanobacteria, an event known as the Great Oxidation.
During all this time, the atmosphere was composed mainly of hydrogen (H2), methane (CH4), ammonia (NH3) and steam (H2O), which determined the conditions for the first bacterial and archaean life forms on the planet.
The paradox of the young and weak sun
One of the problems that scientists have encountered when studying this period is the so-called paradox of the young and weak Sun (also called the Faint Young Sun Paradox in English). According to estimates, 4.000 billion years ago, the Sun was a young star whose luminosity was approximately 30% less than today. This fact should have caused the Earth to remain in a completely frozen state, especially due to the distance from the Sun and the lack of greenhouse gases as we know them today.
However, evidence has been found that the Earth's crust housed liquid water, suggesting that greenhouse gases that existed at the time, such as methane, played a critical role in keeping Earth warm enough to sustain oceans. This is a key piece of the puzzle involving not only Earth's atmosphere, but also planetary habitability.
The role of the first microorganisms
The evolution of life in the atmosphere would not have been possible without the appearance of the first microorganismsThese single-celled organisms, known as cyanobacteria or blue-green algae, began to release oxygen into the atmosphere through the process of oxygenic photosynthesis, about 2.400 million years, which marked the beginning of the so-called Great OxidationThis oxygen not only transformed the primitive atmosphere, but also laid the foundations for the development of new life forms, which were able to use this gas for cellular respiration.
The first life forms, composed of prokaryotic cells, managed to adapt to the harsh conditions of the primitive atmosphere and laid the foundations for the evolution and diversification of multicellular living beings that would appear hundreds of millions of years later.
Impact of the Great Oxidation
The event of the Great Oxidation not only had an impact on the first anaerobic organisms, but also caused a series of glaciations, due to the decrease in greenhouse gases such as methane, which was replaced by carbon dioxide (CO2), less effective at trapping heat.
These glaciations, like the Huronian glaciation, are some of the oldest episodes in Earth's climate history. There was a period when the Earth may have been completely covered by ice, sometimes referred to as the ice age. Snowball EarthDespite these extreme weather events, life managed to thrive, adapt, and continue to evolve.
Origin of life hypothesis
There are several hypotheses regarding the origin of life during this period. The most widely accepted is that of primordial soup, proposed by scientists such as A. Oparin and J.B.S. Haldane, who suggested that the early oceans contained the chemical compounds necessary to form the first organic molecules. These could have interacted under suitable energetic conditions, such as thunderstorms or hydrothermal vents, to form the first amino acids, nucleotides and other molecules essential for life.
Future lines of research
Current studies on the early atmosphere and its relationship to the origin of life open up new avenues of research not only into the past of our own planet, but also into the possibility of life on other worlds. Planets like Mars and the icy moons of Saturn and Jupiter are in the spotlight to understand how life might develop in extreme atmospheric conditions similar to those on Earth in its early years.
As scientists study the ancient fossil microorganisms, such as stromatolites, and analyze the atmospheres of exoplanets, we will understand more about the ability of organisms to transform their environment and the conditions that allow for long-term habitability of a planet.
This new study on the atmosphere of 4.000 billion years ago It provides us with a fascinating window into a critical time in Earth's history that was pivotal to the development of life as we know it.