Boffins achieve greater precision in determining meteorites’ age

July 22nd, 2010 - 5:44 pm ICT by ANI  

Washington, July 22 (ANI): Scientists have aged dated a group of meteorites with far greater precision than previously possible - by using a different type of radioactive dating on a particularly difficult type of specimen to study.

Researchers discovered that the asteroid from which ureilite meteorites are derived differentiated - or separated into parts of different composition - within 5 million years of the formation of the Solar System, said Cyrena Anne Goodrich, senior scientist at the Planetary Science Institute.

She said: “That is a really short time period.”

Goodrich’s research offered dating with approximately 10 times greater precision than previously available.

Most meteorite dating research has looked at two types of meteorite -angrites and eucrites - which contain ample amounts of minerals necessary for the study. Goodrich and her team opted to investigate ureilites.

The project’s radioactive isotope dating methods looked at short-lived radionuclides rather than the long-lived radionuclides that researchers have studied for years.

She said: “Ureilites are the second most abundant group of differentiated meteorites, but they are particularly enigmatic and are very difficult to date because they don’t contain many different minerals.”

Radiometric dating is based on the principle that radioactive elements decay and change into other elements at a constant rate that can be measured in a laboratory. The basic idea behind radioactive dating is that if you can measure the ratio of parent to daughter isotopes in a rock or mineral using a mass spectrometer, which separates isotopes from one another according to their weight, you can calculate its age.

Goodrich said: “Short-lived radionuclides are isotopes that decay much faster than the long-lived ones. In fact, they decay so quickly that any parent atoms that were present at the time the Solar System formed would have completely changed into daughter isotopes a long time ago.

“By measuring the daughter isotopes in several different minerals, it is possible to determine how much of the parent isotope was in the rock when the rock formed, and this value can be compared to a known value for how much of the parent was present at some specific time, say at the formation of the Solar System.”

Goodrich’s research studied how isotopes manganese-53 decays to chromium-53 and aluminum-26 decays to magnesium 26.

She said: “We were able to apply Mn-Cr and Al-Mg dating to ureilites because I discovered some unusual Mn-rich and Al-rich minerals in a couple of rare types of ureilites. The results of our work provide the first high-precision ages dates for ureilites, 4.5639 billion years ago, plus or minus 0.00045 billion years (450,000 years).”

Earlier dating efforts for ureilites offered precision of only plus or minus 6 million years, according to Goodrich.

She said: “The beauty of this technique is that it has much smaller uncertainties than the long-lived radionuclide dating technique, and the development of this method has resulted in scientists using meteorites to work out many details of what happened in our Solar System in the first 5 to 6 million years of its history. In particular, they have been able to reconstruct many details of the early differentiation of planetesimals like asteroids.”

Goodrich’s research appears in Earth & Planetary Science Letters. (ANI)

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