The correct answer is: A. Troposphere.
The troposphere is the lowest layer of Earth’s atmosphere. It extends from the surface of the Earth to an average height of about 12 kilometers (7.5 miles). The troposphere is where most of Earth’s weather occurs. The temperature in the troposphere decreases with increasing altitude. This is because the air in the troposphere is heated by the Earth’s surface. The Earth’s surface absorbs energy from the sun and re-emits it as heat. This heat warms the air in the troposphere. The air in the troposphere is also heated by the friction of air molecules moving over the Earth’s surface. This friction causes the air to warm and rise. As the air rises, it cools and condenses to form clouds. The clouds release water vapor into the atmosphere, which helps to cool the air. The troposphere is a dynamic layer of the atmosphere. The air in the troposphere is constantly moving and changing. This movement of air causes the weather. The weather in the troposphere can be unpredictable and can change rapidly.
The other options are incorrect because they are not the lowest layer of Earth’s atmosphere.
- The stratosphere is the second layer of Earth’s atmosphere. It extends from the top of the troposphere to an average height of about 50 kilometers (31 miles). The stratosphere is where the ozone layer is located. The ozone layer absorbs harmful ultraviolet radiation from the sun.
- The thermosphere is the third layer of Earth’s atmosphere. It extends from the top of the stratosphere to an average height of about 600 kilometers (373 miles). The thermosphere is the hottest layer of Earth’s atmosphere. The temperature in the thermosphere can reach up to 2,000 degrees Celsius (3,632 degrees Fahrenheit).
- The ionosphere is the fourth layer of Earth’s atmosphere. It extends from the top of the thermosphere to an average height of about 1,000 kilometers (621 miles). The ionosphere is named for the fact that it is ionized, meaning that it contains a high concentration of charged particles. The ionosphere is important for radio communications.
- The exosphere is the outermost layer of Earth’s atmosphere. It extends from the top of the ionosphere to an average height of about 10,000 kilometers (6,214 miles). The exosphere is very thin and is not considered to be part of Earth’s atmosphere.