Question

what important discovery did marie tharp and bruce heezen make when mapping the atlantic ocean floor?
ancient fossils preserved under the seafloor
the deepest part of the mariana trench
a flat, featureless ocean bottom
the mid - atlantic ridge with fracture lines

Explanation:

Marie Tharp and Bruce Heezen mapped the Atlantic Ocean floor and discovered the Mid - Atlantic Ridge with fracture lines, which was crucial for the theory of plate tectonics. The other options are incorrect as they are not related to their discovery. Ancient fossils under the seafloor is not their discovery. The Mariana Trench is in the Pacific Ocean, not related to their Atlantic Ocean mapping. The ocean bottom is not flat and featureless as they showed.

Answer:

The Mid - Atlantic Ridge with fracture lines