During Alfred Wegener's time, several key concepts and pieces of evidence related to the theory of continental drift and plate tectonics were not known or well understood. Here are a few of them:
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Mechanism of Continental Drift: Wegener proposed that continents drift over time, but he could not provide a convincing mechanism for how this occurred. He suggested forces like the Earth's rotation and centrifugal forces, but these were not accepted by the scientific community.
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Seafloor Spreading: The concept of seafloor spreading, which provides a mechanism for continental drift by explaining how tectonic plates move apart at mid-ocean ridges, had not yet been discovered. This idea was fully developed in the 1960s by scientists like Harry Hess and others.
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Plate Tectonics: The broader theory of plate tectonics, which incorporated continental drift and explained the movement of the Earth's lithosphere in terms of tectonic plates, had not been formulated. The understanding of Earth's lithosphere and asthenosphere was still in its infancy.
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Paleomagnetism: The field of paleomagnetism, which studies the magnetic properties of rocks to understand the historical movement of tectonic plates, was not yet developed. This evidence would later play a critical role in supporting Wegener’s ideas.
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Age of the Earth and Geological Time Scale: Although the concept of geological time was recognized, the understanding of the Earth's age and the vast timescales involved in geological processes was not as precise as it is today.
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Fossil Correlation: While Wegener did use fossil evidence to support his theory, the understanding of how and why certain fossils were distributed across continents was not fully developed, nor was there a comprehensive understanding of biogeography.
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Geological Evidence: The geological evidence that now supports continental drift, such as the matching geological formations across continents and the identification of mid-ocean ridges as tectonic plate boundaries, was not fully recognized or understood.
Overall, while Wegener laid the groundwork for what would eventually become the theory of plate tectonics, many crucial elements that support and explain continental drift were undiscovered during his time. It wasn't until the mid-20th century that these ideas were fully developed and accepted by the scientific community.