Scientists Explain How Lightning May Have Kick-Started Life on Earth

A new study suggests that cloud-to-ground lightning might have been key in creating the building blocks essential for life on Earth from nitrogen and carbon.

In Earth’s early days, comets, asteroids and lightning between clouds were all considered possible sources of these life-building molecules. However, after the late Hadean Eon—an early period in Earth’s history about 4 billion years ago, marked by intense impacts and volcanic activity—it became rare for organic compounds from space to reach Earth. Therefore, lightning alone was not very effective at generating these compounds in the atmosphere.

Now, research published in Proceedings of the National Academy of Sciences highlights how cloud-to-ground lightning could have been a dependable source of energy, generating high levels of the chemical building blocks needed to start or support life on early Earth.

Researchers from Harvard explored how cloud-to-ground lightning could have driven these important chemical reactions. Led by George McClelland Whitesides, a Harvard professor of chemistry, the team created a laboratory setup to simulate lightning strikes by discharging sparks across air, water and solid surfaces under conditions similar to those on early Earth.

The team analyzed the products formed from the simulated lightning strikes and discovered that lightning converted carbon and nitrogen from the air into biologically useful molecules, which accumulated in the water.

The authors found that lightning creates impressive results by turning carbon dioxide into carbon monoxide and formic acid, as well as converting nitrogen into useful substances like nitrate, nitrite and ammonium. Specifically, for every mole of electrons used, up to 40 moles of carbon dioxide are transformed, and 3 moles of nitrogen are changed into these useful compounds.

“This work highlights the ability of lightning to drive high-voltage electrochemistry across air–water–ground interfaces and convert inert chemicals into reactive intermediates and nutrients that were crucial to emergent life and its early evolution,” the study said.

“Cloud-to-ground lightning could have contributed to additional and plausible sets of starting materials and reaction pathways relevant to the chemical origin of life on Earth,” the study added.

Cloud-to-ground lightning was found to be much more effective at producing these life-essential compounds, compared with lightning between clouds.

When minerals, similar to those found in early Earth’s rocks, were added to the experiments, the presence of sulfide minerals—like those from volcanic areas—greatly increased the production of ammonia, a crucial ingredient for life.

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