Late Cretaceous
The Late Cretaceous Epoch
The Late Cretaceous epoch, a crucial period in Earth's geologic history, spans from approximately 100.5 to 66 million years ago. It marks the latter part of the Cretaceous period, which is itself a division of the Mesozoic Era. This epoch is pivotal due to significant geological, climatic, and biological transformations, including the emergence and diversification of many plant and animal groups and the dramatic Cretaceous–Paleogene extinction event that concluded the period.
Geology and Paleogeography
During the Late Cretaceous, the arrangement of continents and oceans was significantly different from the present day due to plate tectonics. This era witnessed the continued breakup of the supercontinent Pangaea, leading to the formation of the Atlantic Ocean and the development of new oceanic and continental landscapes.
The Western Interior Seaway was a significant inland sea that split the North American continent into eastern and western landmasses. This seaway fostered unique ecosystems and influenced the migration, evolution, and extinction of various species.
Climate
The Cretaceous period was characterized by a relatively warm climate, with the Cretaceous Thermal Maximum marking a peak in global temperatures approximately 90 million years ago. High eustatic sea levels led to widespread shallow seas, which contributed to the deposition of chalk formations, such as the iconic White Cliffs of Dover.
However, towards the end of the Late Cretaceous, there was a general cooling trend, which may have been influenced by volcanic activity, changes in ocean currents, and fluctuations in atmospheric carbon dioxide levels.
Flora and Fauna
The Late Cretaceous saw the proliferation of angiosperms, or flowering plants, which began to dominate terrestrial ecosystems. This floral revolution altered habitats and influenced the evolution of numerous animal species, including insects and herbivorous dinosaurs that relied on these plants.
Dinosaurs continued to be the dominant terrestrial vertebrates. Notable groups such as hadrosaurs, ceratopsians, and theropods thrived, while mammals and birds also diversified. Marine reptiles like mosasaurs and plesiosaurs ruled the oceans, and pterosaurs soared through the skies.
The Cretaceous–Paleogene Extinction Event
The end of the Late Cretaceous is marked by the Cretaceous–Paleogene extinction event, one of the most significant mass extinctions in Earth's history. This event led to the extinction of approximately 75% of species, including all non-avian dinosaurs. It is widely believed to have been caused by a combination of volcanic activity, climate change, and the impact of a massive asteroid, which created the Chicxulub crater in present-day Mexico.
The extinction event had profound impacts on global ecosystems, paving the way for the rise of mammals and the beginning of the Paleogene period, which followed the Mesozoic Era.