What steps does the oceanic lithosphere go through to achieve the ...

[bobbysung]

What steps does the oceanic lithosphere go through to achieve the density required for subduction? Be as specific as possible.
 
  What will be an ideal response?

Question 2

What does the word theory mean when used to define plate tectonic theory or the theory of evolution?
 
  What will be an ideal response?

[aburgess]

Answer to Question 1

The lithosphere becomes denser than the asthenosphere by cooling. As the oceanic lithosphere moves away from the mid-ocean ridge, the lithosphere cools off and becomes denser. The lithosphere also becomes thicker because more of the original asthenospheric mantle becomes part of the cool, solid lithosphere. Once the lithosphere becomes sufficiently thick and dense, it will be able to sink into the asthenosphere due to density contrasts. As the slab sinks, it also reaches metamorphic temperatures and pressures and part of the slab converts into rock that is also very dense (eclogite).

Answer to Question 2

Theories are not speculative ideas. Theories are rigorously tested concepts established as the best explanations for observed natural phenomena known at the time and are widely accepted in the scientific community.

[bobbysung]

Excellent

[bigsis44]

TYSM