Life on earth may owe its existence to an extraterrestrial rock. A new study points to evidence that when meteorites crashed down on earth from space millions of years ago, they brought with them essential ingredients for life.
ATP, adenosine triphosphate, is the molecule that most life, and all advanced life forms such as us, use to store energy. This molecule, made up of, holds energy in a bond, and when that bond is broken, it creates energy that is used for every living function: from metabolism to motion to organ function.
But ATP wasn’t always around. The earliest life forms, which probably formed around 3.6 billion years ago, would most likely have been far too simple to be able to make ATP or the enzymes necessary to release its energy. One hypothesis is that prehistoric life used a simpler energy-storage molecule that wouldn’t have utilized complicated metabolism to produce energy.
Furthermore, the primordial environment on Earth probably didn’t have phosphorous, or if it did, it was trapped inside minerals that primitive life forms wouldn’t have been able to access. If there wasn’t a readily available phosphorous source on early Earth, perhaps the phosphorous came from somewhere beyond our plant.
Terry Kee from the University of Leeds in England worked with other researchers on a recent, as yet unpublished, study to determine if and how extra-terrestrial phosphorous would have been used by the earliest organisms. They simulated primordial Earth by taking samples of volcanic pond water from Iceland; water that they think probably represented the acidic pH of early Earth. Into this “ancient” pond water, they placed fragments of a meteorite from Siberia that had traces of extraterrestrial phosphorous on it.
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The research team’s finding was very telling. When the water evaporated, what remained was pyrophosphite: a simpler energy-storage molecule than ATP. Pyrophosphite is much more reactive than ATP, and doesn’t need complex enzymes to aid in releasing its stored energy. It would have been an easy way for simple organisms to get the energy to subsists on prehistoric Earth.
But, as always in science, there is contention to this theory. Many say that modern living organisms use only phosphates to glean energy. Even tiny microbes that aren’t complex enough to use ATP use pyrophosphate, not pyrophosphite. Some argue that without living proof that pyrophosphite can be used as an energy source, we don’t know this was ever possible. Those on the –phosphite side of the debate say pyrophosphate is far too reactive. It wouldn’t have been accessible on Earth’s surface long before it reacted with water, which also needed to be present in order for life to arise.
Kee is in the process of trying to determine if pyrophosphite can be transformed into pyrophosphate. Perhaps pyrophosphite was the first energy source, and then life evolved to using pyrophosphate, eventually switching to the more complex ATP.
Read more on phosphorous and its extraterrestrial origins at newscientist.com.
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