The correct option is 1 and 2 only.
Explanation
The evolution of the Earth involves a sequence of physical and chemical processes starting from the aggregation of matter to the formation of a layered structure and the development of the atmosphere.
- Statement 1 is Correct: Differentiation is the process by which Earth's materials separated into different layers based on density. As the Earth was in a volatile state, heavier materials (like iron and nickel) sank towards the center to form the core, while lighter materials moved towards the surface to form the crust.
- Statement 2 is Correct: Accretion refers to the gradual accumulation of planetesimals and other matter under the influence of gravity. This process is responsible for the initial formation of planets, including Earth.
- Statement 3 is Incorrect: Degassing is the process through which gases and water vapor were released from the Earth's interior, primarily through volcanic eruptions. This process was crucial for the formation of the atmosphere and oceans, not the core.
- Statement 4 is Incorrect: Photosynthesis is a biological process initiated by early life forms (such as cyanobacteria) much later in Earth's history. It contributed to the oxygenation and modification of the atmosphere, not the formation of the crust.
Key Takeaway: Differentiation explains the layered structure of the Earth (Crust, Mantle, Core), whereas Degassing and Photosynthesis are key processes in the evolution of the Earth's atmosphere.