Chapter 13, Problem 1RQ

To determine

The reason for the rocks that are present on the Earth could not yield isotopic dates older than four billion years.

Answer to Problem 1RQ

The rocks on the Earth could not yield isotopic dates older than four billion years because they might have undergone melting or metamorphic chemical reactions due to high pressure and temperature or erosional effects.

It is also stated by the astronomers that the heavy bombardment of meteorites during 4.1 Ga to 3.8 Ga melted and pulverized the rocks that are present on the Earth.

Explanation of Solution

The rocks present on the surface of the Earth are classified into three types based on their modes of formation: igneous, sedimentary and metamorphic rocks. Isotopic dating is the process of finding the age of the rocks by using the isotopic minerals that are present in the rocks.

By the isotopic dating of meteorites, the age of the Earth is calculated as 4.54 Ga. However, the oldest rock on the surface of the Earth are dated only 4.0 Ga. This calculated time between 4.0 Ga-4.54 Ga is termed as Haden Eon.

The rocks between this period left no mark in the history. The rocks are formed either by the cooling of magma and lava or by the erosion, deposition and compaction of sediments or by the chemical reactions caused due to high temperature and pressure.