Radiometric dating rock strata

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The layers of sedimentary rock, or strata, can be seen as horizontal bands of differently colored or differently structured materials exposed in this cliff.

The deeper layers are older than the layers found at the top, which aids in determining the relative age of fossils found within the strata. Such index fossils must be distinctive, globally distributed, and occupy a short time range to be useful.

There are several different methods for estimating the ages of fossils, including: Paleontologists rely on stratigraphy to date fossils.

Stratigraphy is the science of understanding the strata, or layers, that form the sedimentary record.

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.

(relative geologic timescale) (b) Absolute Dating Following the discovery of radioactivity in 1895, radiometric dating techniques were developed to determine the absolute ages, i.e. In the succession of strata, each layer represents the geographical conditions that occurred over that area at the time the layer was deposited.

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(a) Relative Dating This technique uses principles of stratigraphy (rock strata) and the study of fossils (palaeontology) to determine the relative ages of rocks and sediments. Field geologists' rely on a number of simple techniques for dating rocks and constructing geological successions. The Law of Strata Identified by Fossils is a little bit more complex.

Strata are differentiated from each other by their different colors or compositions and are exposed in cliffs, quarries, and river banks.

These rocks normally form relatively horizontal, parallel layers, with younger layers forming on top.

Long before geologists tried to quantify the age of the Earth they developed techniques to determine which geologic events preceded another, what are termed "relative age” relationships.

These techniques were first articulated by Nicolas Steno, a Dane living in the Medici court of Italy in the 17th C.

If a fossil is found between two layers of rock whose ages are known, the fossil's age is thought to be between those two known ages.

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