Correct Option
The correct option is 2 and 3 only.
Explanation
The evolution of Earth's atmosphere is generally classified into three stages: the loss of the primordial atmosphere, the evolution of the atmosphere through hot interior degassing, and the modification of the atmospheric composition by the biosphere (living world).
Statement-wise Analysis
- Statement 1 is Incorrect. The early atmosphere was not rich in free oxygen. The primordial atmosphere consisted mostly of hydrogen and helium, which were stripped away by solar winds. The secondary atmosphere, formed through degassing, was a "reducing atmosphere" containing gases like nitrogen, carbon dioxide, methane, and ammonia, but virtually no free oxygen. Free oxygen appeared much later, primarily due to biological activity.
- Statement 2 is Correct. During the cooling of the Earth, gases and water vapour were released from the interior solid earth through a process called degassing. This process released large quantities of water vapour, carbon dioxide, nitrogen, and small amounts of methane and ammonia, forming the bulk of the early secondary atmosphere.
- Statement 3 is Correct. The composition of the atmosphere was significantly modified by the living world through the process of photosynthesis. Early life forms, specifically cyanobacteria (blue-green algae), began using carbon dioxide and releasing oxygen. Over billions of years, this biological process saturated the oceans and atmosphere with oxygen, leading to the current oxidizing atmosphere.
Key Takeaway: Earth's early atmosphere was reducing and lacked free oxygen. The transition to an oxygen-rich atmosphere (Great Oxidation Event) was driven by the emergence of photosynthetic life forms that consumed carbon dioxide and released oxygen.