1 For an observer on the ground with eye level at h = 5 ft 7 in (1.70 m), the horizon is at a distance of 2.9 miles (4.7 km). 2  For an observer standing on a hill or tower 100 feet (30 m) in height, the horizon is at a distance of 12.2 miles (19.6 km).
The mantle is a layer of the Earth between the crust and the core. The upper mantle starts below the crust and goes down to a depth of around 200 miles to the boundary with the lower mantle. The temperature of the mantle ranges from 900 degrees Fahrenheit near the crust to as high as 7000 degrees near the core.he Upper Mantle: Temperature and Depth. The upper mantle begins just beneath the crust and ends at the lower mantle. The thickness of the upper mantle is between 200 and 250 miles.
The gases evolved during the melting of Earth's mantle have a large effect on the composition and size of Earth's atmosphere. Uppermost mantle. A thin crust, the lower part of the lithosphere, surrounds the mantle and is about 5 to 75 km thick. There are two main zones in the upper mantle. The uppermost mantle plus overlying crust are relatively rigid and form the lithosphere, an irregular layer with a maximum thickness of perhaps 200 km, of which the uppermost mantle is 120 to 50 km thick.