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In fact, even in younger rocks, absolute dating is the only way that the fossil record can be calibrated.

Without absolute ages, investigators could only determine which fossil organisms lived at the same time and the relative order of their appearance in the correlated sedimentary rock record.

Since parent uranium atoms change into daughter atoms with time at a known rate, their relative abundance leads directly to the absolute age of the host mineral.

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Although with clever detective work many complex time sequences or relative ages can be deduced, the ability to show that objects at two separated sites were formed at the same time requires additional information.

A coin, vessel, or other common artifact could link two archaeological sites, but the possibility of recycling would have to be considered.

In addition, because sediment deposition is not continuous and much rock material has been removed by erosion, the fossil record from many localities has to be integrated before a complete picture of the evolution of life on Earth can be assembled.

Using this established record, geologists have been able to piece together events over the past 635 million years, or about one-eighth of Earth history, during which time useful fossils have been abundant.

To achieve this precision, geochronologists have had to develop the ability to isolate certain high-quality minerals that can be shown to have remained closed to migration of the radioactive parent atoms they contain and the daughter atoms formed by radioactive decay over billions of years of geologic time.

In addition, they have had to develop special techniques with which to dissolve these highly refractory minerals without contaminating the small amount (about one-billionth of a gram) of contained lead and uranium on which the age must be calculated.

" There are also apps for Apple, Android and other devices that help track refund status.

The IRS started processing most returns on January 29, but will not start processing returns with the Earned Income Tax Credit (EITC) or Additional Child Tax Credit (ACTC) until mid-February 2018.

Local relationships on a single outcrop or archaeological site can often be interpreted to deduce the sequence in which the materials were assembled.

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