The seasonality that resulted from the close approach of the Moon finally began to manifest itself at the Cretaceous-Tertiary boundary by modifying the environment of the Earth, causing periodic ice ages and the associated fluctuations in ocean levels. Prior to the close approach there was only insignificant axial tilt of the Earth’s axis and therefore no significant seasons. During the Jurassic, seasonality was cloaked by the Earth’s dense atmosphere. During the Cretaceous, the beginning of seasonality can be found but it was tempered by the great expanse of ocean which made for a relatively temperate marine climate throughout the world. At the Cretaceous-Tertiary Boundary the seas began to retreat to their modern levels and as larger areas of the continents are above sea level seasonality finally began to become apparent. The transition between the Cretaceous and the Tertiary is the point at which seasonality begins to drive evolution on Earth.
As the impact of seasons began to play itself out, the new continents were moving into more polar latitudes, exacerbating the effects of seasonality. Climates changed and temperatures fluctuated. The introduction of new landmasses into the Earth’s polar regions provided platforms for the accumulation of modern continental ice sheets. This would ultimately play an important role in modern global sea levels.
Once these radical changes began occurring at the end of the Cretaceous, the animals most ready to adapt became the ones to survive. Birds had developed feathers for mating rituals but found them more useful for shelter in the slowly evolving colder climates. Feathers allowed birds to adapt with the cooling seasons by allowing for insulation from the cold and combined with the ability for flight, allowing for migration.
Mammals also were prepared for a cooling trend in the Earth’s environments. Fur like feathers allowed for thermal protection and opened new territory for species diversification unobtainable by the previous dominant species of amphibians, reptiles, and dinosaurs.
Did you know?
A large reptile which managed to survive into the modern world is the sea turtle, an aquatic species able to migrate. The sea turtle is very strongly tied to the Moon and tide cycle of the modern age. In a Darwinian twist the sea turtles that adapted to the new high tide regime survived presumably by laying their eggs farthest up the beach.
Over the millions of years since the peak of the Jurassic it is seen that the largest animals could not survive, and less well adapted creatures were restricted to specialized environments because of the changes in atmospheric pressure and temperature. Toward the end of the Mesozoic small warm-blooded animals, which were prepared to adopt personal thermal envelopes, were less impacted by seasonality. In addition, angiosperms rapidly evolved to fill the void left by plants unable to thrive under this new seasonal regime.
The tilting of the Earth, initiated by the approaching Moon, caused seasonality and the Earth’s latitudinal climactic zones. The building of mountain chains associated with plate movements combined with shifting climactic zones produced the multitude of micro-niches of our modern world. Witness to this event is an eventual supremacy of furred and feathered species, the blossoming of flowering plants, and their specific evolution with the seasonal climate. Deciduous trees became conspicuous and began to dominate the landscape by the close of the Cretaceous.