The smoother areas of the 660-km boundary could result from more thorough vertical mixing, while the rougher, mountainous areas may have formed where the upper and lower mantle
don't mix as well.
In a process known as subduction, which occurs where crustal plates collide, slabs of cold oceanic crust sink all the way down to the core-mantle boundary, making it easy for heat to escape the core through the lower mantle
. This cooling mechanism drives the churning convective motions in the outer core that stirs up Earth's dynamo.
We quantified systematically eye numbers on the mantles of sea scallops (Placopecten magellanicus) to determine whether they varied with scallop size (which is correlated with age), or between upper and lower mantles
. We predicted (1) smaller scallops, which are more vulnerable to predators, would have more eyes than larger scallops; and (2) because the upper mantle is hypothesized to be in a better position to detect predators, the upper mantle will have more eyes than the lower mantle
The developments high dense mineral polymorphs in the lower mantle
induce cracks, creeps and faults in the lower mantle
Models with progressively weaker lower-mantle regions (i.e., progressively lower viscosities within the lower mantle
) will have shorter decay times, and will thus have reached a state closer to their final equilibrium state by the present day.
(See "Conduits Into Earth's Inaccessible Interior" page 7.) This strongly suggests that distinct geochemical reservoirs exist in the mantle, and seems to favor a layered convection model with different mantle compositions in the upper and lower mantle
Laboratory tests by Japanese researchers indicated that a huge amount of water may be trapped in minerals in the lower mantle
- a thick hot layer extending from 406 miles below the Earth's surface to a depth of 1,800 miles.
As you continue the journey down through the upper and lower mantle
, the temperatures increase.
Deeper inside Earth, in the lower mantle
or the core, temperatures are too high for diamonds to form.
The most common mineral in Earth's lower mantle
is perovskite, a silicate whose crystalline structure can't store many stray hydrogen atoms (which end up in water).