Radioactive dating of fossils definition

13-Apr-2020 14:22 by 9 Comments

Radioactive dating of fossils definition

Just as the use of the fossil record has allowed a precise definition of geologic processes in approximately the past 600 million years, absolute ages allow correlations back to Earth’s oldest known rocks formed more than 4 billion years ago.In fact, even in younger rocks, absolute dating is the only way that the fossil record can be calibrated.

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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.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.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.Where this occurs at the edge of a continent, as along the west coast of North and South America, large mountain chains develop with abundant volcanoes and their subvolcanic equivalents.These units, called igneous rock, or magma in their molten form, constitute major crustal additions.When rocks are subjected to high temperatures and pressures in mountain roots formed where continents collide, certain datable minerals grow and even regrow to record the timing of such geologic events.

When these regions are later exposed in uptilted portions of ancient continents, a history of terrestrial rock-forming events can be deduced.

The same margin of error applies for younger fossiliferous rocks, making absolute dating comparable in precision to that attained using fossils.

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.

Similarly, in geologic studies, vast quantities of information from widely spaced outcrops have to be integrated.

Some method of correlating rock units must be found.

In the ideal case, the geologist will discover a single rock unit with a unique collection of easily observed attributes called a marker horizon that can be found at widely spaced localities.