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.
Definition. The upper mantle is defined as that part of the mantle between the crust and the phase transition of Î³-olivine to perovskite. The total mass of the upper mantle is 1.06 Ã 10 24 kg, about a quarter of the total mass of the mantle. Its volume, 2.95 Ã 10 11 km 3, is a third of the total volume of the mantle. Until the discovery of a major transition near 660-km depth, the upper mantle was better known as Bullenâs âlayer B,â extending to 400-km depth.