How lightning changes rocks – Reduction of phosphorus minerals

Featured Image: Lightning is a common high energy phenomenon on Earth, like here during a storm over Bucharest, Romania. Image credit: Catalin.Fatu (Wikimedia Commons), CC BY-SA 3.0.

Papaer: Lightning strikes as a major facilitator of prebiotic phosphorus reduction on early Earth

Authors: Benjamin L. Hess, Sandra Piazolo, Jason Harvey

You might think of lightning as a violent and destructive force of nature, but it might have helped to spark life on Earth. The enormous energy released by lightning can weather or even melt rocks. During this short but intense heating phase, the rock’s or soil’s mineralogy changes and a very important element for life becomes available: phosphorus. A group of researches was able to show why the transformation of phosphorus minerals by lightning could have been an important source of this element during Earth’s infancy.

Most minerals incorporate phosphorus in its oxidised form, phosphate. A team of geoscientists studied the mineralogical changes in soils after lightning strikes. When a thunderbolt hits the ground, minerals in the soil can be heated to temperatures of up to 3000 K, way more than enough to melt them, and glassy tubes called fulgurites can form. The researchers analysed the composition of fulgurites to better understand their formation. They discovered high temperature minerals, such as silicon carbide and schreibersite, one of the few minerals which contain phosphide. In contrast to phosphate, phosphide, the reduced form of phosphorus, is soluble in water and therefore accessible for biochemical reactions. A single strike converted about 35 to 55% of the soil’s phosphate to phosphide. Schreibersite is normally found only in meteorites. Understanding the formation of schreibersite might help to solve the important question of how phosphorus became available for the chemical reaction on our young planet which led to the emergence of the very first living organism.

A Fulgurite found in Florida. The lightning strike melted the soil for a very short time. During solidification, the melt formed a glass tube around the impact area. Image credit: Mario Hendriks (Wikimedia Commons), CC BY-SA 3.0.

How can these rare minerals be produced by a thunderbolt? Soils contain carbonates, which are formed when rocks weather in the presence of CO2 and water. When soil is melted by a lightning strike, carbon from the carbonates forms a graphitic compound, which is highly reducing. Under these extremely hot and reducing conditions, iron and phosphate are reduced and the odd mineral schreibersite can form. Over time, the fulgurite will weather and the phosphide will be dissolved into water, ready to participate in biochemical reactions.

To estimate if this process could also have happened on the early Earth, the researches compared the contents of iron and phosphorus in rocks from the Archean period to modern fulgurites. Indeed, these old rocks could have been a promising environment for the generation of schreibersite by lightning. Moreover, we know from the composition of very old zircon minerals, that our young planet supported the existence of oceans. So, there should have been enough water in the atmosphere to form clouds. And with clouds come rain and lightnings. Based on our knowledge on the atmospheric properties in the Archean, the production of phosphide by lightning was maybe of the order of 100 to 10000 kg per year. In this way, storms and lightning strikes might have literally sparked the emergence of life by making phosphorus available for biochemical reactions.

‘How lightning changes rocks – Reduction of phosphorus minerals’ by Max Winkler is licensed under a Creative Commons Attribution-ShareAlike 4.0 International License.

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