Life on Earth originated billions of years ago. While there was likely plenty of water and carbon dioxide in the atmosphere to work with – essential ingredients for life – most of Earth’s phosphorus was locked up in insoluble rock, making it impossible to combine into organic phosphates. Phosphorus is considered one of the key elements for life. It is involved in biomolecules such as DNA and RNA and thus plays a role in all life processes from movement to growth to reproduction.
During the Late Heavy Bombardment (4.1 – 3.8 billion years ago), meteorites delivered minerals to the Earth, including small amounts of a mineral called schreibersite ((Fe,Ni)3P) which is made partly of phosphorous and is soluble in water. If tons of schreibersite-bearing meteorites crashed into Earth over millions of years, then theoretically, enough phosphorus could be released to create conditions ripe for life. However, about the time when life actually emerged on Earth near 3.5 billion years ago – the age of the earliest known microfossils – the rate of meteorite impacts dropped exponentially as the planets and moons of the Solar System took shape. So, is there another way to make schreibersite?
New research is showing that lightning strikes may have been just as significant in life developing on Earth. When lightning discharges into the ground, it can sometimes cause soil, sand, rock and/or organic debris to fuse together and form rocks called “fulgurites.” While analyzing a particularly large specimen of fulgurite formed from a clay-rich soil in the state of Illinois (USA), researchers found that it contained a large amount of schreibersite spherules, leading them to investigate just how much lightning would be needed to potentially spark life.
In the modern-day, over the course of a year, Earth sees about 560 million lightning bolts. Billions of years ago, when the Earth’s atmosphere was richer in carbon dioxide (and therefore hotter and more prone to storms), it’s hypothesized that billions of bolts could have lit up the planet, releasing usable phosphorus on land. Over the timeframe of a billion years, lightning strikes could theoretically produce thousands of pounds of phosphorus per year. Of course, there’s a lot of uncertainty about conditions of early Earth, but, even on the lower end of phosphorus production, lightning could have made a difference for the emergence of life. Whether lightning struck enough exposed land on early Earth to make an impact on life is a question that can never be fully answered, but this new study shows that, at least mathematically, it was possible. It may be that a combination of asteroid impacts and lightning strikes ultimately gave Earth the phosphorus it needed for DNA and RNA to develop. But further studies of early terrestrial life should keep lightning in mind.
Read more here: https://www.nature.com/articles/s41467-021-21849-2
Image: “Lightning Composite” by b_napper is licensed with CC BY-NC 2.0. To view a copy of this license, visit https://creativecommons.org/licenses/by-nc/2.0/