What happened during this time?
Increased northern and southern regional differences in floras.
First flowering plants appear on the landscape (~130 Ma)
By the Late Cretaceous, forests evolved to look similar to present-day forests, with oaks, hickories, and magnolias becoming common in North America
New kinds of dinosaurs appear
First pachycepalosaurid dinosaurs
First fossils of many insect groups
Modern mammal groups arise
Birds evolve from therapod lineage
Extinction of non-avian dinosaurs and ammonites
Carbon dioxide level begin ~1,330 ppm and rise to over 2,000 ppm by the end of the Early Cretaceous. During the Late Cretaceous levels fall to ~1,000 ppm
Oxygen levels begin at ~20.5% and increase to ~22.5% by the end of the period
Large-scale geographic isolation, causing a divergence in evolution of all land-based life for the two new land masses
Extensive new coastlines, and a corresponding increase in the available near-shore habitat.
Seasons grow more pronounced as the global climate became cooler
At end of the Cretaceous Period, an asteroid hits Earth in the Yucatan Peninsula, Mexico, forming what is today called the Chicxulub impact crater
It has been estimated that half of the world's species went extinct at about this time, but no accurate species count exists for all groups of organisms
Some have argued that many of the species to go extinct did so before the impact, perhaps because of environmental changes occurring at this time