Meteorites may have delivered phosphorus

From Philadelphia, at a meeting of the American Chemical Society

Phosphorus is an essential atomic ingredient in DNA, RNA, and cell membranes. But, compared with other must-have elements such as carbon, hydrogen, oxygen, and nitrogen, phosphorus is the least abundant on Earth, says Matthew Pasek of the University of Arizona in Tucson. With so little phosphorus in the terrestrial environment, Pasek wondered how life could have emerged on Earth 4.5 billion years ago. The answer, he proposes, is meteorites.

Phosphorus occurs naturally on Earth in the form of the mineral apatite. However, previous experiments showed that dissolving apatite in water releases only small amounts of phosphorus, presumably not enough to have supported the origin of life.

In recent years, evidence has been accumulating for the theory that meteorites supplied Earth with large amounts of organic material, providing the necessary building blocks for making the first forms of DNA, proteins, and cells. Pasek and his colleagues theorized that meteorites could have delivered phosphorus as well.

Meteorites carry phosphorus mostly in an iron-nickel phosphide mineral known as schreibersite. So, the researchers mixed schreibersite with water to see what chemicals would leach out. They found that several different phosphorus-containing compounds emerged, one of which was phosphate, a key player in photosynthesis and many other biochemical reactions. The amount of phosphate released from schreibersite was 10,000 times that produced by a similar watery preparation of apatite.

The researchers suspect that iron meteorites brought phosphorous compounds to Earth since that type of meteorite is known to contain significantly more schreibersite than other types do.