The correct option is 1 and 3 only.
Explanation
The troposphere is the lowermost layer of the atmosphere where almost all weather phenomena occur. Its thickness is not uniform across the Earth; it varies significantly with latitude and season due to thermal expansion and atmospheric dynamics.
Statement-wise Analysis:
- Statement 1 is Correct: The height of the troposphere extends up to approximately 18 km at the equator. This is the region of maximum thickness due to high temperatures and strong vertical air movement.
- Statement 2 is Incorrect: The height of the troposphere is not uniform. At the poles, the air is colder and denser, resulting in a much lower height of approximately 8 km.
- Statement 3 is Correct: The variation in height is primarily caused by the transport of heat by strong convectional currents. At the equator, intense solar heating generates powerful updrafts that push the air to greater heights, expanding the layer. Conversely, at the poles, low temperatures cause the air to compress and settle lower.
Key Takeaway:
The troposphere is thickest at the equator (~18 km) and thinnest at the poles (~8 km) because strong convectional currents caused by intense heat at the equator push the atmospheric layer upwards.