. Explain The Three Methods for Dating vthe Rocks


Best Answer

1. RADIOACTIVE METHODS

Radioactive Uranium method (238U): The half-life period (during which half of the material is decayed) of this uranium is ~4.5 billion (4.5 × 109 years). After emitting   and   particles it is finally changed into stable lead (206Pb).

It can be used for dating the fossil/rock of more than 50 million years old.

Potassium argon method (40K): The half life period of this radioactive isotope is 1.3 billion years. This method has been used for dating the hominid fossil + of Africa (Zinjanthropus/Australopithicus).

Radioactive Carbon method (14C): The half life period of this carbon is ~5750 years. After emitting  -particles it changes into 14N. This method can be used for dating recent fossils (up to 10 × 104 years).

2. THERMOLUMINESCENT METHOD

In this method the rock mineral is heated to above 500°C and the trapped electrons are released, creating a flash of light called Thermoluminescence. The intensity of the luminescence (light emission) can be measured to determine the amount of time when this mineral was last heated.

This method is suitable for the samples that range in age from few hundred years to about 500,000 years (e.g. minerals of Quaternary Period).

This method is suitable for the minerals of Quartz, feldspar, zircon, flint, calcite etc. which have been previously heated to above 500°C. Such samples include remains of ceramics, bricks, hearths, fire pits, kilns, smelter walls etc.

3. ELECTRON SPIN RESONANCE (ESR) METHOD

It is also based on the accumulation of trapped electrons in minerals: more the trapped electrons in mineral, the older the sample/fossil is.

ESR is also called Electron Paramagnetic Resonance. It relies on changes in electron-orbits with spins caused by radioactivity overtime.

It can be used for time periods up to 2.0 million years. It works best on carbonate-minerals, e.g. coral reefs and tooth enamel.

 

 

 

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