4. What kept the concept of continental drift from originally being

accepted?

The fact that there was no driving force or motive mechanism behind the theory of continental drift.

Explanation:

The concept of continental drift was first proposed by Abraham Ortelius in 1596, and further improved on by Alfred Wegener in 1912. The theory proposes that the earth's continents have moved across the ocean bed. The continents also move with geologic time relative to each other. The concept was not accepted by scientists because there was no driving force or motive mechanism to explain the theory.

A scientist named Alfred  Holmes, came up with the mantle convection theory which explains that the slow motion of the earth was caused by convection currents. This explanation was still not satisfactory to scientists. Today, the theory of plate tectonics has gained more acceptance than the theory of continental drift.

they are all solids.