GEOLOGY
Carbon ratios suggest life present early in Earth's days
Tuesday, August 26, 2008 3:10 AM
By Dale Gnidovec Most people have heard of carbon dating, a process that measures the amount of radioactive carbon-14 present in an object.
It can date objects to about 50,000 years ago, so it is good for dating events in archaeology and the last part of the Ice Age. For older materials, geologists must use other radioactive elements such as rubidium, potassium, lead or uranium.
Lucky for us, most of the carbon in our bodies is not the radioactive isotope C-14 but rather C-12, with a very small amount of C-13. The ratio of those two nonradioactive isotopes of carbon is well-known for various kinds of rocks, the oceans and atmosphere.
A recent article in the journal Nature reported some interesting results of analyzing the C-12 to C-13 ratio in microdiamonds and graphite inclusions contained in crystals of the mineral zircon from an area called the Jack Hills of Western Australia.
The zircons are the oldest crystals known on Earth -- they formed 4.2 billion years ago -- so they are like time capsules. Because the diamonds are found inside, they must have formed before the zircon crystals enclosed them.
The microdiamonds had surprisingly low ratios of C-13. One possible explanation is that they represent meteorites that bombarded the planet early in its history. Many meteorites are characterized by low C-13 ratios.
Another possibility is that chemical reactions in Earth's early atmosphere, which contained large amounts of hydrogen and methane, might have produced the low ratios.
The researchers also suggested an even more intriguing explanation: Life processes produce residues with greatly reduced C-13 ratios. If the low C-13 ratios in the microdiamonds from Australia were produced by living organisms, there was life on this planet more than 4.2 billion years ago, almost as soon as it formed.
That suggests life might be present in many parts of the universe.
Dale Gnidovec is curator of the Orton Geological Museum at Ohio State University.
Gnidovec.1@osu.eduhttp://www.dispatch.com/live/content/science/stories/2008/08/26/sci_gnidovec26.ART_ART_08-26-08_B5_E9B31DN.html?sid=101
