Who made contact with East Africa before Europeans?

At a continent-continent convergence,

Sandstones that form in aeolian (wind/desert) environments appear very different from other sandstones, such as those formed in a beach/ shoreline environment and in rivers on land. give three identifying properties for each of the three sandstones that would tell a geologist which depositional environment they formed in. consider things such as the relationship between transportation and grain size, shape, roundness, sorting, fossils and composition.

Which are evidence of the seafloor spreading? a. molten material b. magnetic stripes c. continental material d. drilled core samples e. ocean water samples