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 (磷) 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 first locked inside minerals that cannot dissolve in water.
Until now, it was widely believed that meteorites (陨石) 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 can be dissolved in water, where life is thought to have formed.
The researchers say levels of phosphorus minerals caused by lightning strikes were found to have been higher about
3.5 billion years ago. The researchers think this was about the age of the earliest-known fossils widely accepted to be those of microorganisms. 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.
New research does not completely cancel the theory that meteorites could have been another source of life-giving phosphorus. Meteor (流星) strikes around the time of the appearance of life are far less than thought a decade ago.
