Meteorites Donated Life’s Phosphorus

image_credit: James V. Scotti, UA Lunar & Planetary Lab
Artist’s illustration of early Earth, 4.5 billion years ago, about a year after a Mars-sized object hit Earth and formed the Earth-Moon system. The still molten moon with an impact in progress (upper left) is viewed from Earth’s volcanic surface. Meteorites and comets — like the comet visible in the sky — delivered materials needed for life on Earth. Rings remaining from the collision and other debris, including moonlets not yet swept up by the moon, are visible. An Orion-like nebula appears at upper right.
Image Credit: James V. Scotti, UA


Their research shows that meteorites easily could have provided more phosphorus than naturally occurs on Earth — enough phosphorus to give rise to biomolecules which eventually assembled into living, replicating organisms.

Phosphorus is central to life. It forms the backbone of DNA and RNA because it connects these molecules’ genetic bases into long chains. It is vital to metabolism because it is linked with life’s fundamental fuel, adenosine triphosphate (ATP), the energy that powers growth and movement. And phosphorus is part of living architecture – it is in the phospholipids that make up cell walls and in the bones of vertebrates.

"In terms of mass, phosphorus is the fifth most important biologic element, after carbon, hydrogen, oxygen, and nitrogen," said Matthew A. Pasek, a doctoral candidate in UA’s planetary sciences department and Lunar and Planetary Laboratory.



Image Credit: Virginia Smith, UA Lunar & Planetary Laboratory

Pasek cites recent studies that show there’s approximately one phosphorus atom for every 2.8 million hydrogen atoms in the cosmos, every 49 million hydrogen atoms in the oceans, and every 203 hydrogen atoms in bacteria. Similarly, there’s a single phosphorus atom for every 1,400 oxygen atoms in the cosmos, every 25 million oxygen atoms in the oceans, and 72 oxygen atoms in bacteria. The numbers for carbon atoms and nitrogen atoms, respectively, per single phosphorus atom are 680 and 230 in the cosmos, 974 and 633 in the oceans, and 116 and 15 in bacteria.

"Because phosphorus is much rarer in the environment than in life, understanding the behavior of phosphorus on the early Earth gives clues to life’s orgin," Pasek said.


Pasek began working with Dante Lauretta, UA assistant professor of planetary sciences, on the idea that meteorites are the source of living Earth’s phosphorus. The work was inspired by Lauretta’s earlier experiments that showed that phosphorus became concentrated at metal surfaces that corroded in the early solar system.


"Meteorites have several different minerals that contain phosphorus," Pasek said. "The most important one, which we’ve worked with most recently, is iron-nickel phosphide, known as schreibersite."


Pasek with lab equipment. The tube contains a meteorite sample dissolved in fresh water.
Credit: UA










Pasek is talking about the research at the 228th American Chemical Society national meeting in Philadelphia. The work is funded by the NASA program, Astrobiology: Exobiology and Evolutionary Biology.