Question

why lithosphere also called crust

Answer 1

The Lithosphere is called Crust because

Lithosphere is the hard rocky surface of the earth's biosphere which mainly comprises mountains, plains, seabeds and other rocky structures.
Crust is the uppermost rocky part of the earth's surface
And as Both Crust and Lithosphere have same characteristics and meaning
Therefore they both are considered same

Answer 2

Answer:

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The concept was based on the presence of significant gravity anomalies over continental crust, from which he inferred that there must exist a strong, solid upper layer (which he called the lithosphere) above a weaker layer which could flow (which he called the asthenosphere).