Answer to Question 1
The Earth system is composed of four parts:
i. The atmosphere: A thin layer of gases that surrounds Earth
ii. The hydrosphere: Composed of various reservoirs of water, including ice
iii. The biota: Includes all living organism
iv. The solid Earth: Includes all rocks, including those in both the crust and the mantle. The iron core is also part of the Earth system because it is there that Earth's magnetic field is generated.
Answer to Question 2
Greenhouse gases are gases that warm a planet's surface by absorbing outgoing infrared radiation (radiant heat) and reradiating some of it back toward the surface. This process is called the greenhouse effect. The greenhouse effect is a natural physical process that operates in all planetary atmospheres. Global warming is a warming of Earth's atmosphere caused by an anthropogenic enhancement of the greenhouse effect.