lithospher

definition: 
he rigid outer part of the earth, consisting of the crust and upper mantle.
sentence: 
After new oceanic crust forms, the lithosphere cools and thickens as it moves away from the ocean ridge. An alternative to an active mantle thermal anomaly is greater stretching of the mantle lithosphere than the crust
difficulty: 
medium
toefl frequency: 
1
toefl classification: