Why wasn't oxidation type chemical weathering common more than 2 billion years ago?

            Due to deficiency of Oxygen in atmosphere.

Explanation:

                   Oxidation is defined in two ways, 1) The addition of Oxygen and Removal of Hydrogen 2) The removal of electrons.

                   We will discuss the first definition for this question. The addition of oxygen to various compounds results in the oxidation of that compound.

Example: Oxidation of Methane;

                                   CH₄  +  2 O₂    →    CO₂  +  2 H₂O

In this example oxygen is added to methane and hydrogen is being removed from methane.

Oxidation type chemical weathering common more than 2 billion years ago because of less amount of Oxygen in atmosphere and the oxygen which was produced by plants reacted with different metals like Iron forming precipitates which precipitated to the bottom of oceans.

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the answer is b. dilution