What seems to have prevented corals from forming massive reefs before Oligocene time?

The Oligocene epoch is a geological period that occurred approximately 34 to 23 million years ago. This period is known for significant changes in the Earth's climate and the appearance of massive coral reefs due to various factors such as seawater chemistry, climate change, and the evolutionary development of corals.

Before the Oligocene epoch, the Earth's climate was relatively warm, with higher CO2 levels, which might have been unsuitable for the formation of extensive coral reefs. The Oligocene epoch marked a significant shift in the Earth's climate towards cooler conditions, which allowed corals to thrive in more extensive areas of shallow seas.

One of the significant factors affecting the formation of coral reefs is the chemistry of seawater. Before the Oligocene epoch, the seawater may have had lower levels of calcium carbonate, which is the primary building block for coral skeletons. This reduced availability of calcium carbonate could have limited the potential for coral reef development. During the Oligocene epoch, geological events led to an increase in the concentration of calcium carbonate in the seas, providing an ideal environment for coral growth.

The evolution of coral species played a significant role in the formation of massive coral reefs during the Oligocene. Before the Oligocene epoch, the diversity of coral species may have been limited, restricting their ability to form large and complex reef structures. As coral species diversified through natural selection and evolution, they became more capable of forming vast reef systems, which became more evident during the Oligocene epoch. In conclusion, several factors, including climate change, seawater chemistry, and the evolution of coral species, seem to have been critical in preventing the formation of massive coral reefs before the Oligocene epoch. These factors contributed to creating the necessary conditions for coral reefs to thrive and led to the emergence of extensive reef systems during the Oligocene.