Life on Earth may have been born in the chaos of volcanic lightning: ScienceAlert
The chaos of sky-piercing lightning is believed to play a key role in liberating elements such as phosphorus, making them accessible to thriving life on ancient Earth.
Now, scientists have found geological evidence that lightning discharges associated with volcanic events may also have played a role in fixing nitrogen, making it available for biological processes as well.
Since Earth is thought to have been more volcanically volatile in its younger years, this discovery suggests that rampant volcanic activity may have been crucial to the emergence of life as we know it.
“For the first time, significant amounts of nitrate have been detected in volcanic deposits from very large explosive eruptions,” wrote a team led by geologist Adeline Arosky of the Sorbonne University.
“These results provide geological support for the unique role that subaerial explosive eruptions play in high-energy-demanding processes, which were essential in providing the building blocks of life during its emergence on Earth.”
border-frame=”0″ allow=”accelerometer; autoplay; write to clipboard; encrypted media; gyroscope; picture-in-picture; web-sharing”allowfullscreen>
Somehow, when the Earth was wild and young, processes on our planet transformed a mixture of ingredients into the materials needed to start life. One of the things life needs is nitrogen, an essential nutrient for building things like proteins, amino acids, and nucleic acids.
The Earth has large amounts of nitrogen. About 78% of the atmosphere consists of this substance. But biology cannot access it in its atmospheric form of molecular nitrogen, or N2; Nitrogen atoms need to separate from each other and attach to other atoms to form more reactive compounds, such as nitrate or ammonia.
Now that life exists, biological processes such as those that occur in microbes that live in plant roots can speed up the process. Human industrial technologies can also pump nitrogen and pump compounds like ammonia by the tank load.
But before there could be life, a non-biological process was needed to initiate nitrogen fixation. Here comes the role of electricity – lightning. Electrical discharges can fix nitrogen, as was first established in 1784.
Because lightning is ubiquitous during volcanic eruptions, caused by huge billowing ash clouds, scientists have thought that volcanic lightning may have played a role in triggering the nitrogen cycle before life made its way into the world.
Experimental studies have shown that this is possible, but geological evidence for fixed nitrogen as a result of this process has been weak on Earth.
Arosky and her team found this evidence, in the form of nitrates buried in ancient volcanic sediments. They collected samples from a number of volcanic deposits resulting from explosive eruptions in Turkey and Peru, which occurred between 1.6 and 20 million years ago, and looked specifically for nitrate, the end product of nitrogen oxidation.
They found large concentrations of nitrates in all the sediments they sampled, with features suggesting that most of them formed during volcanic eruptions. This was remarkable, the researchers said.
They also sampled younger volcanic deposits, approximately 75,000 to 55,000 years old, from less explosive eruptions; There they also found nitrates.
There was no correlation between the age of the deposit and the nitrate concentration, which means, the researchers believe, that the deposition of the compounds is not the result of gradual processes that occur over long periods of time. Nitrates are thrown into volcanic rocks in one fell swoop.
Concentrations of sulfur and chlorine in the sediments were also consistent with a volcanic origin. Taken together, this suggests that volcanic lightning could fix nitrogen in quantities large enough to play a role in the emergence of life.
It could give us a tool to interpret other nitrate deposits around the world. In the Atacama Desert, for example, the presence of nitrates has been attributed to atmospheric deposition, because oxygen isotope ratios were thought to be not possible with volcanic deposition. The team’s findings show that such connections are possible in large explosive events.
“The discovery of nitrate in volcanic sediments makes it the first field and geological archive evidence of nitrogen fixation by volcanic lightning, and this could have important implications,” the researchers wrote.
“We estimate that, on average, about 60 teragrams of nitrogen could be fixed during a large explosive event. Our findings point to the unique role that subaerial explosive eruptions could play in providing the essential ingredients for the emergence of life on Earth.”
The research was published in Proceedings of the National Academy of Sciences.