Scientists uncover ancient source of oxygen that could have fueled life on early Earth

Most likely, this oxygen source existed before photosynthesis.

The planet's crust was torn open by violent earthquakes that rocked Earth some 3.8 billion years ago, allowing chemical reactions to take place deep under the shattered rock. According to a recent research, these reactions, which were fuelled by seismic activity, water, and almost boiling temperatures, may have given oxygen to some of the first living forms on Earth.

According to the research, which was released on Monday (August 8), in the journal Nature Communications, this oxygen would have been packed in the chemical combination hydrogen peroxide (H2O2), which has two hydrogen atoms and two oxygen atoms bonded together (opens in new tab). Although hydrogen peroxide is perhaps best known for its antiseptic properties, it can still be a useful source of oxygen once it is broken down by enzymes or reactions that take place under high heat, according to Jon Telling, senior author of the study and senior lecturer in geochemistry and geomicrobiology at Newcastle University in the U.K.

Now, Telling and his coworkers have discovered in laboratory studies a mechanism whereby large quantities of hydrogen peroxide may have developed on early Earth and therefore acted as a possible oxygen supply for some of the planet's oldest life. The researchers discovered that although these processes are most effective at temperatures close to the boiling point of water (212 degrees Fahrenheit, or 100 degrees Celsius), they may still release a small amount of H2O2 at lower temperatures.

These temperatures are significant because they fall within the range that thermophiles and hyperthermophiles, or heat-loving bacteria and archaea, are known to flourish in, according to Telling. In principle, this enigmatic ancient organism may have been impacted by the presence of hydrogen peroxide formed deep in the planet's crust as it is believed that the common ancestor of all life on Earth also evolved to exist in intensely heated settings.

Importantly, early organisms would have required methods to "detoxify" the substance if it was present in their environment because hydrogen peroxide can harm cells' fats, proteins, and DNA, according to Lynn Rothschild, a senior research scientist at the NASA Ames Research Center in California who was not involved in the new study. Since hydrogen peroxide is also a result of photosynthesis, organisms have to first develop the ability to cope with it in order to develop the capacity for photosynthesis.

Before the emergence of oxygenic photosynthesis, "there had to be sources of reactive oxygen species" on early Earth, including hydrogen peroxide, according to Rothschild for Live Science.

inside the crust, deep

Previous(opens in new tab) investigations showed that minerals hypothesized to exist in the early Earth's crust might be a potential source of hydrogen peroxide and, consequently, a potential source of oxygen. These studies included work conducted by Rothschild's team.

In several of these tests, rocks were crushed under specified circumstances, and subsequently the crushed rocks were submerged in water. On a tiny scale, this sequence of occurrences resembles the physical strain that rocks through in tectonically active areas of the early Earth's crust, when the crust broke apart and allowed water to pour within. According to Telling, when Earth was less than a billion years old, the globe did not yet have vast slabs of crust moving across its mantle like tectonic plates do now. He said that at the time, the crust was still subject to localized buckling and cracking brought on by volcanic activity and interactions between much smaller crustal fragments.

Previous investigations showed that this early tectonic activity would be able to create hydrogen gas (a component of hydrogen peroxide) and fully-formed hydrogen peroxide, but these tests only produced modest quantities of these substances. Similar tests were performed in the latest study by Telling and his colleagues, but the crushed rocks were subjected to a wider range of temperatures and were left exposed for up to a week. On the basis of earlier research, they hypothesized that this strategy may increase the production of hydrogen peroxide.

The group employed basalt and peridotite, which would have been prevalent in the oceanic crust of the early Earth, as well as granite, a rock present in continental crust, in their rock-crushing tests. They carefully moved the crushed rock to airtight bottles, added water, and then turned up the heat after grinding the stone to a fine powder in oxygen-free containers.

Near-boiling temperatures caused the rock powders' component minerals' "defects" to become less stable and more susceptible to react with water. These flaws specifically included "peroxy linkages," or regions in the crystal structure of the minerals where two oxygen atoms are bonded together whereas normally oxygen would only attach to the element silicon. Inadvertently adding water to a crystal's structure as it develops might result in the introduction of such flaws, according to Telling.

He stated that these faults "may really kind of dislocate" when the peroxy links in the rocks are stressed. They are able to travel through the crystal structure to the surfaces, where they may begin to interact with water. This contact produces hydrogen peroxide as a result.

These findings imply that hydrogen peroxide may have been a prevalent component of the environment, at least in areas of the early Earth that were shaken by earthquakes and cooked at high temperatures. However, as Telling pointed out, the tests can't precisely replicate the rate or size at which these H2O2-producing processes occurred on the early Earth.

According to Rothschild, who investigates the origins and development of life on the early Earth and maybe elsewhere in the galaxy, "it would be intriguing to determine how prevalent this occurrence is" and how hydrogen peroxide affected the evolution of early species globally. That being said, H2O2 wouldn't have required to be present in every location on early Earth for it to have had a significant impact on the development of life there. You're only affected by the chemicals in your local environment if you're a microscopic bacterium that is only a few microns wide.

If you have reactive oxygen species in your area, it's okay, according to Rothschild. According to her, this early exposure to ambient H2O2 may have served as crucial "training" for the creatures that developed into cyanobacteria, the blue-green algae in charge of filling the atmosphere with oxygen and influencing the evolution of our planet.