In a study published Tuesday in the journal Nature Communication, minerals generated by lightning strikes revealed that storms on Earth billions of years ago may have delivered one of the main ingredients of life.
The origins of life on Earth are enshrouded in mystery. Scientists have suggested that meteorites may have delivered key ingredients to life on Earth after crash landing on our home planet.
However, the new study suggests that lightning played a pivotal role in creating one of the key ingredients for life: phosphorus.
WHAT'S NEW — Phosphorus is considered one of the main key ingredients for life, and serves in the backbone of DNA and is contained within the cell membranes of all living organisms. However, how it arrived on Earth is still up for debate. In addition, many phosphorus sources are locked within rock or insoluble in water.
As a bolt of lightning hits the Earth, it heats up or vaporizes surface rock. In turn that frees up phosphorus locked inside, which then creates glassy rocks called fulgurites. A mineral compound containing phosphorus called schreibersite is soluble in water, where life is thought to have first formed on Earth.
HERE’S THE BACKGROUND — Life is believed to have started forming on Earth between 3.5 to 4.5 billion years ago. Scientists believed that phosphorus was mainly delivered to Earth by way of meteorites, as some space rocks contain schreibersite.
However, in the time frame during which life was beginning, the rate of meteorite impacts on Earth had significantly decreased, but the rate of lightning strikes remained constant. They were especially common in tropical regions, which were more conducive to creating soluble phosphorus because of the water vapor in the air.
Benjamin Hess, a graduate student in Yale's Department of Earth & Planetary Sciences and lead author of the study, says in a statement that this shows that lightning made significant contributions to kicking off life on Earth.
"It makes lightning strikes a significant pathway toward the origin of life," Hess says.
How they did it — The scientists behind the new study analyzed an especially large fulgurite sample from lightning that struck the backyard of a home in Glen Ellyn, Illinois in 2016. They fired lasers, X-rays, and electrons at the fulgurites sample to see how it would interact with the material in order to determine its composition.
They discovered about 100 grams of schreibersite fragments inside the fulgurites.
The team then estimated the amount of lightning that would have struck Earth around 4.5 to 3.5 billion years ago when the first signs of life began emerging. Early Earth saw 1 to 5 billion lightning flashes every year, compared to about 560 million flashes per year today, according to the researchers.
Of those early flashes, anywhere from 100 million to 1 billion would have struck the ground annually, creating fulgurites from surface rocks.
Therefore, primordial lightning strikes could have catalyzed 110 to 11,000 kilograms of phosphorus-containing compounds each year.
That amount of phosphorus would have been sufficient to help ignite the first seeds of life, according to the study.
"This work helps us understand how life may have formed on Earth and how it could still be forming on other, Earth-like planets," Hess says.
What’s next — The recent findings suggest that phosphorus may have found its way on Earth through lightning strikes, but that doesn’t eliminate other sources by which the remaining key ingredients to life would have been found on early Earth.
In order for life to begin, our planet also needed water, carbon, hydrogen and other organic compounds which may have been delivered by meteorites or shed by stars.
Scientists will continue to examine meteorites that are found on Earth, as well as the composition of flying asteroids, in order to put together pieces of the puzzle of how life emerged on our home planet.
Abstract: When hydrated, phosphides such as the mineral schreibersite, (Fe,Ni)3P, allow for the synthesis of important phosphorus-bearing organic compounds. Such phosphides are common accessory minerals in meteorites; consequently, meteorites are proposed to be a main source of prebiotic reactive phosphorus on early Earth. Here, we propose an alternative source for widespread phosphorus reduction, arguing that lightning strikes on early Earth potentially formed 10–1000 kg of phosphide and 100–10,000 kg of phosphite and hypophosphite annually. Therefore, lightning could have been a significant source of prebiotic, reactive phosphorus which would have been concentrated on landmasses in tropical regions. Lightning strikes could likewise provide a continual source of prebiotic reactive phosphorus independent of meteorite flux on other Earth-like planets, potentially facilitating the emergence of terrestrial life indefinitely.