VOA慢速英语2021--研究称闪电可能有助于地球上生命的发展（在线收听）

Study: Lightning May Have Helped Life Develop on Earth

A new study suggests lightning strikes that hit Earth after its formation may have unlocked a necessary chemical element to support the beginning of life.

Researchers say the lightning may have supplied enough phosphorus to Earth during the first billion years after the planet was formed. Scientists believe life started on Earth about 3.5 to 4.5 billion years ago.

Phosphorus is an important element for the formation of life. It helps form cell structures and supports DNA, the material present in nearly all living organisms. But on early Earth, phosphorus is believed to have been locked inside minerals that cannot dissolve in water.

Until now, it was widely believed that meteorites that struck Earth were mainly responsible for the presence of "bioavailable" phosphorus. Some meteorites contain a phosphorus mineral called schreibersite, a highly reactive mineral that can form organic molecules.

But when lightning strikes the ground, it can create glassy rocks called fulgurites by super-heating and sometimes vaporizing rocks on the surface. This process frees the phosphorus locked inside. As a result, these fulgurites can contain schreibersite, which is soluble in water, where life is thought to have formed.

Researchers in the United States and Britain estimated that early Earth saw 1 to 5 billion lightning strikes hit Earth each year - compared to about 560 million yearly today. That would add up to 1 quintillion strikes after a billion years, forming at least 1 billion fulgurites.

A study describing the research results recently appeared in the publication Nature Communications.

The researchers said phosphorus minerals caused by lightning strikes were found to have been higher by about 3.5 billion years ago. This is about the age of the earliest-known fossils widely accepted to be those of microorganisms, the researchers found.

"Lightning strikes, therefore, may have been a significant part of the emergence of life on Earth," said Benjamin Hess, a Yale University graduate student in earth and planetary sciences. He was the lead writer of the study.

Hess told Reuters news agency that unlike meteorite hits that generally decrease over time, lightning strikes can happen continuously over a planet's history. He added that this means lightning strikes may also be a very important element for providing the phosphorus needed for the emergence of life on other Earth-like planets.

The researchers also examined an unusually large fulgurite formed when lightning struck near a home outside Chicago, Illinois in 2016. "Our research shows that the production of bioavailable phosphorus by lightning strikes may have been underestimated," study co-writer Jason Harvey told Reuters. He is a professor of geochemistry at Britain's University of Leeds.

Among the materials considered necessary for life are water, carbon, hydrogen, nitrogen, oxygen, sulfur and phosphorus, along with an energy source.

Scientists believe the earliest bacteria-like organisms were formed in Earth's early waters. But there is a debate over when this happened and whether it happened in warm and shallow waters or in deeper waters.

Hess said that new research does not completely cancel the theory that meteorites could have been another source of life-giving phosphorus.

"Meteor impacts around the time of the emergence of life are far less than thought a decade ago," Hess said. "But I don't see our work as a competition against meteorites as a source of phosphorus. The more sources, the better," he added.

Words in This Story

dissolve – v. to turn from a solid into a liquid

meteorite – n. a piece of rock or metal that has fallen to the ground from outer space: a meteor that reaches the surface of the Earth without burning up entirely

quintillion – n. a number equal to 1 followed by 18 zeros

fossil – v. part of an animal or plant from thousands of year ago, preserved in rock

emerge – v. to appear from somewhere

source – n. something that provides what is wanted or needed

shallow – adj. not deep

impact – n. an act or event in which something strikes another thing

decade – n. a period of 10 years