Old ancient stones measure wrongly for millions of years!

The geochemists have been working hard to determine the age and reconstruct the history of the earth and the solar system. They use the phenomenon of radioactive decay like "natural watches".

These two special types of watches are the two Samarium chemical elements (denoted by Sm) and Uranium (U) that exist in ancient stone samples.

The accuracy of 'natural watches' plays an extremely important role in accurately reconstructing the history of the universe's formation and evolution, namely the solar system and our earth.

For example, "if there is an important event in the history of the earth, such as the extinction of a species or climate change, or due to the impact of meteorites, one needs to know the absolute ages of the event with the highest reliability , " said Joe Hiess (British Geological Society) who chaired one of the studies. Relative age is also necessary, because: "In Earth Science, it is necessary to determine which events happen first, what happens after."

However, according to the New York Journal, the results of the new study indicate that the two best types of 'natural clocks' of solar systems have also revealed certain deviations.

Zircon helps look to the past (Photo: Science / AAAS)

That is, a radioactive isotope of the Samarium element decays much faster than previous studies, and different isotopes of Uranium do not always appear in the same proportions in rocks. on the earth. Therefore, the age of the oldest rocks is misidentified for millions of years.

Samarium "Clock"

Geochemists determine the age of ancient rocks by measuring the ratio of radioactive isotopes of the same element in a rock sample. Since the decay rate (or half-life - the amount of radioisotope reduction giảm) of these radioactive isotopes is constant, the age of the stone can be determined if the ratio of isotopes is known. rock.

Of course, they must know their half-life. And if the value of the half-life is inaccurate, the result of the age of the antiquity will be misleading.

One of the isotopes is often chosen to determine the early events of the solar system, Samarium Sm-146 , a heavy metal, metallic isotope found in many minerals of the earth's crust. .

Scientists have measured the half-life of Sm-146 four times in the last 60 years and obtained different results for each measurement. The latest two results seem to be compatible with a half-life of 103 million years with a plus and minus 5 million years error.

But Paul and the others suspect that this result is not very good. They use a technology called accelerator mass spectrometry , which Paul thinks has little experimental error.

They found that the half-life was only 68 million years, 30% less than previous results. It means that the stones are aged by decay of Sm-146, which includes the oldest aged rocks on the earth, the moon, and also meteorites from Mars, formed earlier from 20 million to 80 million years compared to previous studies.

Uranium clock

The oldest rocks were also dated with Uranium isotopes when it decayed into Lead isotopes.

Unlike the case of the 'Samari' clock, in the Uranium clock the deflection of the age of the antiquity is not due to the difference in the half-life measurement.

Until the last few years, geochemists have assumed that the ratio of Uranium U-238 on U-235 is constant, equal to 137.88 in all rocks. So just measuring the ratio of lead isotopes can determine the age of the stones. But high-precision measurements for materials found in meteorites and rocks formed in the ocean indicate differences.

Hiess and colleagues conducted the largest research on the proportion of uranium isotopes, using 45 zircon samples from all over the world. Zircon is one of the first minerals to solidify on the earth, withstand weathering and melting, retain uranium, and is a mineral suitable for dating ancient rocks.

The team found that most samples had the same ratio of uranium isotopes, but some samples had very different proportions.'Assume that the ratio of unmodified uranium isotopes is no longer true'.

The team gave a new rate of new average uranium isotopes. This result changed a bit the age of the oldest rocks, less than about 1 million years. The oldest rocks will have the largest correction results: sedimentary rocks have a age of 4.4 billion years determined to be younger than 0.7 million years. To make it easier to imagine, if the earth is 18 years old, the age of the oldest rocks will be reduced by one day.

Now scientists know they need to accurately measure the ratios of uranium isotopes in all rock samples, along with the ratio of lead isotopes to determine the age of the rocks more accurately.

Finally, it should be emphasized that the accuracy of these 'natural watches' plays a very important role in arranging past events. For example, if mass extinctions occur just before the meteorite plunges into the earth, it will be different from meteorites hitting the earth before extinction.

Reference: Newscientist