Phosphorus from asteroids may have sparked life on the Earth, according to new investigations of ancient limestone. The oceans of early Earth could have been seeded with this vital ingredient for the formation of life by meteorites containing schreibersite, an iron-nickle material infused with phosphorus.
Matthew Pasek, an astrobiologist from the University of South Florida, led a team who uncovered evidence that asteroids colliding with Earth during the Hadean and Archean eons were carrying reactive phosphorus. This salt, when mixed with water, is essential in the formation of pre-biotic materials which can lead to simple life.
Current understanding is that the earliest life on the planet depended solely on RNA, before the development of DNA. The problem with that theory so far has been trying to determine how RNA was able to acquire its needed phosphorus.
"Meteorite phosphorus may have been a fuel that provided the energy and phosphorus necessary for the onset of life," Pasek said.
Pasek and his team studied phosphorus deposits in limestone from the Archean eon, which began 3.8 billion years ago, and lasted 1.3 billion years. The oldest known fossils are dated to 3.5 billion years ago. The meteoric phosphorus they found, if added to simple organic molecules, could produce identical biomolecules to those essential for life today.
Terrestrial sources of phosphorus were not common enough at the time to provide early organic chemistry with the phosphorus need to spark life. Meteors, however, might have supplied enough phosphorus to the world's early oceans, producing phosphite, to bring about the reactions needed for life to begin three-and-a-half billion years ago.
"[T]he minerals likely corroded in water, releasing large amounts of phosphorus in a form only found during Earth's early formation. The phosphite would have likely resulted in an adjusting of the chemistry of Earth's early oceans, with its chemical signature later becoming trapped in marine carbonate where it was preserved," researchers said.
Phosphite is no longer found in great quantities in Earth's oceans, due to the radically different geological nature of our planet today compared to water composition billions of years ago. Phosphorus in today's oceans is too unreactive and insoluble to play the role that phosphite did back in the Archeaon eon. Researchers argue that this is the reason we do not see new forms of RNA spawning independently of life forms today.
The samples studied were found in Austrailia, Zimbabwe, Wyoming, Florida and West Virginia.
The article announcing the findings were published in the Proceedings of the National Academy of Sciences.
