Solar System: Age determination was a matter of luck

Relationship of uranium isotopes used for dating not stable as previously assumed

Asteroids in the early solar system © NASA / Spitzer Telecope
Read out

The fact that researchers correctly determined the age of our solar system was more of a matter of luck. Because, as it turns out, one of the basic assumptions for age determination, the constant ratio of the two uranium isotopes 238 and 235, is wrong. This is shown by new analyzes of meteorites, which have now been presented in "Science".

Our solar system is made of stardust. This comes from stars that exploded millions or even billions of years before the birth of our solar system. Such supernova explosions produced heavy elements, including uranium. The currently accepted age of our solar system is 4.567 billion years. Scientists determined it in 2002 based on the radioactive decay of uranium to lead, the gold standard of age determination in the geo and planetary sciences. To this radioactive

To be able to apply clock precisely, however, one must know exactly the relationship of the two long-lived uranium isotopes 238U / 235U. So far, this ratio was considered constant.

Now, however, Frankfurt geoscientists have shown, together with colleagues from Arizona State University, that there are significant variations in the uranium isotope in the very oldest material of the solar system, the meteorites. If one had used the recently studied calcium-aluminum-rich inclusions (CAIs) of some meteorites for age determination, the solar system would have been dated up to five million years too old.

Curium changed ratio of uranium isotopes

The scientists around Stefan Weyer now show that at the birth of our solar system, a so-called trans-uranium - the element curium - existed. According to the researchers, the curium, which has not previously been taken into account for the uranium isotope of meteorites, stems from a star explosion that occurred about 100 million years before the birth of our solar system. display

The isotope 247Cm of the element named after the two-time Nobel laureate Marie Curie decays with a half-life of approximately 15 million years in 235U, one of the two remaining uranium isotopes. In this way, the ratio of uranium isotopes shifts in favor of the 235U.

Is the age of the solar system still correct?

Do we have to completely revise the age of the solar system? "The situation is probably not that serious, " said Weyer, who oversaw the research project during his time at the Goethe University. As the researcher, who now works at the University of Cologne, explains, there were also age determinations on other materials from the early solar system, which formed only shortly after the calcium-aluminum-rich inclusions (CAIs) in the meteorites. In these materials was probably also significantly less curium, so that there were only minor deviations from the known uranium isotope.

Luck had

"So, presumably, the age testers were lucky and did not catch any CAIs that were overly affected by the curium breakdown". However, in order to be able to better determine the age of the solar system in the future, Weyer intends to combine the uranium-lead clock of CAIs - the oldest material in our solar system - with precise uranium isotope measurements in a new research project.

(University of Frankfurt am Main, 20.01.2010 - NPO)