Final answer:
The ocean was likely its deepest over Laurentia and Gondwana during the Cambrian and Ordovician periods of the Paleozoic Era, correlating with the times of high sea levels and notable marine life diversification.
Step-by-step explanation:
During the Paleozoic Era, particularly the Cambrian and Ordovician periods, the ocean was likely at its deepest over what is now known as the landmasses of Laurentia and Gondwana. During the Cambrian period, there was a remarkable diversification of life, including many new types of organisms such as sponges and trilobites, indicating a marine environment rich in biodiversity. As the Ordovician period progressed, invertebrates continued to thrive, and the first fish appear, marking an even deeper and more diverse ocean.
Figure 29.21 suggests that throughout the Paleozoic Era, starting around 550 million years ago with the formation of Gondwana, and later with the rise of Laurentia close to the equator, sea levels were exceptionally high. This would imply that during both the Cambrian and Ordovician periods, which span approximately 544 to 440 million years ago, the seas were at a particularly great depth, facilitating the evolution of a wide variety of marine life.By the end of the Paleozoic Era, with the closing of the Permian period, extraordinary changes occurred, including the largest mass extinction event known as the Permian extinction. However, it was during these earlier periods, the Cambrian and Ordovician, that the oceans were most expansive and deep, contributing to the extensive marine biodiversity of the era.