Can someone define mesosphere (mantle)- Upper and lower?

http://www.windows2universe.org/earth/Atmosphere/mesosphere.html

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The mesosphere refers to a layer of Earth's atmosphere, specifically within the mantle region. It is located between the stratosphere and the thermosphere. The mesosphere can be further divided into two parts: the upper mesosphere and the lower mesosphere.

To define the mesosphere, we need to understand the different layers of Earth's atmosphere and their characteristics, which can be obtained through scientific research and observation. Here's a step-by-step breakdown on how you can define the upper and lower mesosphere:

1. Begin by researching the Earth's atmosphere layers: The atmosphere is divided into several layers based on changes in temperature and composition. The most commonly recognized layers are the troposphere (closest to Earth's surface), stratosphere, mesosphere, and thermosphere.

2. Understand the characteristics of the mesosphere: The mesosphere is the third layer of the atmosphere, located above the stratosphere and below the thermosphere. It is characterized by decreasing temperatures with increasing altitude.

3. Differentiate the upper and lower mesosphere: Since the mesosphere is a continuous layer, the upper and lower mesosphere are not distinct sub-layers with specific boundaries. Instead, they represent different altitudes within the mesosphere.

4. Altitude range of the upper mesosphere: The upper mesosphere generally starts around an altitude of approximately 85 kilometers (53 miles) above Earth's surface and extends upward to about 100 kilometers (62 miles).

5. Altitude range of the lower mesosphere: The lower mesosphere begins around 50 kilometers (31 miles) above the Earth's surface and extends up to the upper mesosphere at around 85 kilometers (53 miles).

By understanding the general characteristics and altitudes associated with the mesosphere, you can define the upper and lower parts within this layer. It's important to note that the mesosphere does not have well-defined boundaries, and the transition between the upper and lower mesosphere is gradual rather than abrupt.