BONN: Primordial lightning strikes may have helped life emerge on Earth

BONN: The emergence of the Earth’s
first living organisms billions of years ago may have been facilitated by a
bolt out of the blue – or perhaps a quintillion of them.

The emergence
of the Earth’s first living organisms billions of years ago may have been
facilitated by a bolt out of the blue – or perhaps a quintillion of them.

Researchers
said on Tuesday that lightning strikes during the first billion years after the
planet’s formation roughly 4.5 billion years ago may have freed up phosphorus
required for the formation of biomolecules essential to life.

The study
may offer insight into the origins of Earth’s earliest microbial life – and
potential extraterrestrial life on similar rocky planets. Phosphorus is a
crucial part of the recipe for life. It makes up the phosphate backbone of DNA
and RNA, hereditary material in living organisms, and represents an important
component of cell membranes.

On early
Earth, this chemical element was locked inside insoluble minerals. Until now,
it was widely thought that meteorites that bombarded early Earth were primarily
responsible for the presence of “bioavailable” phosphorus. Some
meteorites contain the phosphorus mineral called schreibersite, which is
soluble in water, where life is thought to have formed.

When a
bolt of lightning strikes the ground, it can create glassy rocks called
fulgurites by super-heating and sometimes vaporizing surface rock, freeing
phosphorus locked inside. As a result, these fulgurites can contain
schreibersite.

The
researchers estimated the number of lightning strikes spanning between 4.5
billion and 3.5 billion years ago based on atmospheric composition at the time
and calculated how much schreibersite could result. The upper range was about a
quintillion lightning strikes and the formation of upwards of 1 billion
fulgurites annually.

Phosphorus
minerals arising from lightning strikes eventually exceeded the amount from
meteorites by about 3.5 billion years ago, roughly the age of the
earliest-known fossils widely accepted to be those of microbes, they 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 and lead author of the study published in the journal
Nature Communications.

“Unlike
meteorite impacts which decrease exponentially through time, lightning strikes
can occur at a sustained rate over a planet’s history. This means that
lightning strikes also may be a very important mechanism for providing the
phosphorus needed for the emergence of life on other Earth-like planets after
meteorite impacts have become rare,” Hess added.

The
researchers examined an unusually large and pristine fulgurite sample formed
when lightning struck the backyard of a home in Glen Ellyn, Illinois, outside
Chicago. This sample illustrated that fulgurites harbor significant amounts of
schreibersite.

“Our
research shows that the production of bioavailable phosphorus by lightning
strikes may have been underestimated and that this mechanism provides an
ongoing supply of material capable of supplying phosphorous in a form
appropriate for the initiation of life,” said study co-author Jason Harvey,
a University of Leeds associate professor of geochemistry.

Among the
ingredients 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 arose in Earth’s primordial
waters, but there is a debate over when this occurred and whether it unfolded
in warm and shallow waters or in deeper waters at hydrothermal vents.

“This
model,” Hess said, referring to phosphorous unlocked by lightning,
“is applicable to only the terrestrial formation of life such as in
shallow waters. Phosphorus added to the ocean from lightning strikes would
probably be negligible given its size.”