When Earth formed 4.5 billion years ago, any phosphorus that was present
likely sank into the molten core because of the element's distinct chemical
properties. However, phosphorus is essential for life; it is found in DNA,
RNA, and other important biological molecules. So it is probable that the
phosphorus that made life possible was delivered to Earth's surface from
extraterrestrial origins, and previous studies have suggested meteorites as
potential sources.
Now, Plane et al. present a new analysis suggesting that much smaller
extraterrestrial particles known as cosmic dust may deliver phosphorus to
Earth's atmosphere, where a series of chemical reactions repackage the
element into biologically useful forms—namely, metal phosphites and
phosphates—that eventually settle onto Earth's surface.
Upon entry into the atmosphere, air friction causes cosmic dust to undergo a
process of vaporization and melting known as ablation. The new research
builds on earlier work in which cosmic dust–sized meteoric fragments were
flash heated to simulate ablation and the release of phosphorus-containing
molecules was detected. Computational modeling of this process provided
further support for cosmic dust as a significant source of phosphorus on
Earth's surface.
The researchers constructed a network of chemical reactions that outline the
specific process by which cosmic dust ablation could produce biologically
useful phosphorus molecules. To do so, they combined real-world results from
laboratory studies of chemical reactions with theoretical predictions for
reactions that have not yet been studied in the lab. Then the researchers
incorporated the reaction network into a global climate model.
The reaction network and the model simulations provide new support for the
ablation of cosmic dust and subsequent chemical reactions as a source of
biologically useful forms of phosphorus. These molecules are incorporated
into tiny "meteoric smoke" particles that settle onto Earth's surface. The
authors suggest the particles could be a significant and continuous supply
of phosphorus for life on Earth.
In addition, the researchers predict which regions, per year, might receive
the greatest amount of phosphorus delivered by cosmic dust, in particular,
the northern Rockies, the Himalayas, and the southern Andes. They also
predict that a narrow atmospheric layer of OPO—a phosphorus-containing
molecule—might encircle Earth 90 kilometers above its surface.
Future research could confirm the existence of the predicted layer.
Researchers could also explore the possible role of cosmic dust–delivered
phosphorus during the rise of life on Earth, when limited amounts of
phosphorus could have constrained biological activity.
Reference:
John M. C. Plane et al, Phosphorus Chemistry in the Earth's Upper
Atmosphere, Journal of Geophysical Research: Space Physics (2021).
DOI: 10.1029/2021JA029881
Tags:
Space & Astrophysics