1. Lack of a plausible mechanism: In the early 20th century, scientists did not have a clear understanding of how the continents could move across the Earth's surface. The theory of plate tectonics, which provides the modern explanation for continental drift, was not developed until the 1960s.

2. Apparent fixity of the continents: Based on their observations, many scientists believed that the continents were fixed in their current positions. They pointed to the lack of evidence for recent large-scale continental movements, such as the absence of folded mountain ranges or deep ocean basins along continental margins.

3. Insufficient fossil evidence: Critics of continental drift argued that the fossil record did not support the idea that the continents had been connected in the past. They pointed out that different continents have distinct assemblages of plants and animals, suggesting that they had always been separate.

4. Doubts about the age of the Earth: At the time, many scientists believed that the Earth was much younger than it actually is. This limited the amount of time available for the continents to have drifted to their current positions.

5. Bias towards gradualism: Many scientists were influenced by the prevailing belief in uniformitarianism, which held that geological processes have always been gradual and unchanging. Continental drift, which proposed the rapid movement of continents, challenged this assumption and was therefore met with skepticism.

Despite these objections, continental drift was eventually accepted by the scientific community as more evidence emerged, including from paleomagnetism, the study of the Earth's magnetic field recorded in rocks, and from seafloor spreading, which provided the mechanism for plate movement.