By what means did life appear on Earth? Researchers have wondered for centuries. New research suggests that primordial lightning strikes may have played a crucial role in allowing the release of phosphorus.
To develop life, you must have the right ingredients. And among them are phosphates. These ions, made up of three oxygen atoms and one phosphorus atom, form part of the backbone of DNA, RNA and ATP (the main source of energy for cells). In fact, they are essential to all known forms of life. The question is: how did the Earth acquire these essential compounds?
Meteors loaded with schreibersite
About four billion years ago, most of the planet’s natural phosphorus contained insoluble rocks. Impossible under these conditions to be able to transform them into organic phosphates.
One theory holds that our young planet may have fired these meteor compounds carrying schreibersite. It is a mineral partly composed of phosphorus, which is also soluble in water. If these schreibersite-laden sky strikes had crashed on Earth for enough time, then phosphorus could have been released in a concentrated area, thus providing the conditions for life to emerge.
That said, around 3.5 billion to 4.5 billion years ago, when life on Earth first manifested, simulations claim that the rate of meteor strikes had already dropped exponentially. . This is why the theory of “interstellar phosphorus” does not convince everyone.
A study published this Tuesday in Nature communications offers an alternative. The work, led by Benjamin Hess of Yale University, speculates that billions upon billions of lightning strikes hitting early Earth may have helped unlock crucial phosphorus compounds.
A quintillion of love at first sight
We know that lightning strikes can heat matter to near 2,760 degrees Celsius, which allows the formation of new minerals. In the new study, Hess and his team analyzed a rock struck by lightning, called fulgurite, excavated in Illinois (United States). The researchers then discovered that small balls of schreibersite had indeed formed in the rock, along with a host of other glassy minerals.
Next, the authors investigated whether enough lightning could have struck early Earth to release a significant amount of the element into the environment.
Thanks to models taking into account the atmospheric composition of our planet at that time, the researchers were able to calculate the number of annual lightning strikes of the primitive Earth. Answer: between a billion and five billion, against a little more than 500 million nowadays. On this sample, they estimate that between 100 million and a billion lightning bolts then hit the land masses each year (the rest being discharged over the oceans).
Finally, over a billion years, up to a quintillion (a 1 followed by 18 zeros) of lightning strikes could have struck our young Earth, each time a little phosphorus. The team calculated that between 4.5 billion and 3.5 billion years ago, lightning strikes alone could have delivered 110 to 11,000 kg of phosphorus per year.
So has lightning struck enough exposed land to favor the appearance of living things on Earth? This is a question we will probably never have a definitive answer to. Still, according to this study, mathematically, it is indeed possible.