What is the lowermost layer of the earth? 

troposphere

The correct answer is option 2. troposphere.

The lowermost layer of the Earth is the troposphere. The troposphere extends from the Earth's surface to a height of about 6 to 10 kilometers (4 to 6 miles) above the equator and 4 to 6 kilometers (2 to 4 miles) above the poles. It contains about 75% of the Earth's atmosphere and nearly all of its water vapor. This is the layer where most weather phenomena, such as clouds, rain, and snow, occur.

Here is a quick explanation of the other answer choices:

• Stratosphere: The layer above the troposphere, extending from about 10 to 50 kilometers (6 to 31 miles) above the Earth's surface. The temperature in the stratosphere increases with height due to the presence of ozone, which absorbs ultraviolet radiation from the sun.
• Ionosphere: The upper layer of the Earth's atmosphere, extending from about 50 to 1000 kilometers (31 to 621 miles) above the Earth's surface. The ionosphere is characterized by the presence of ions and free electrons, which can affect radio waves.
• Mesosphere: The layer above the stratosphere and below the thermosphere, extending from about 50 to 85 kilometers (31 to 53 miles) above the Earth's surface. The temperature in the mesosphere decreases with height.