5 - Cretaceous Paleogene: 65Ma скачать в хорошем качестве

5 - Cretaceous Paleogene: 65Ma

The Cretaceous period is renowned for its warm and temperate mean global climate, although the period was subject to steady and gradual cooling in its final megaannums (intervals of 1 million years) (MacLeod_2011). A marked decrease in pCO2 from 70-65Ma is suggestive of global cooling, however in this 'greenhouse' stage of Earth history global mean temperature reached 22-25 celsius, roughly 7 degrees warmer than 20th century mean levels (Taylor_2011). During the Cretaceous Dinosaurs moved to occupy the ecological niches vacated at the Triassic-Jurassic extinction, becoming the dominant and wide-ranging biotic 'success story' of this period. No other clade of animals noted in the fossil record quite capture the attention of so many in popular society. Whether that is owed to their representation in popular culture, or simply their inherent physical characteristics, these 'terrible lizards' have a knack of striking awe and wonder into us. I make no exceptions in my own representation of their presence as a focalpoint of this piece. Similarly, no other trigger for an extinction quite captures our imagination than that thought to be responsible for the Cretaceous-Paleogene extinction. Whether the bolide impact crater observed at the Yucatan peninsula in Mexico is the signature of the culprit itself, or a later, larger still bolide impact whose crater continues to evade us ought claim responsibility the evidence for meteorite impact within a 500kyr window of the extinction is compelling (Keller_2008). Globally observed layers of Iridium and a huge leap in global atmospheric CO2 concentration following the boundary and hallmarks of an 'impact winter' strongly indicate the trigger being an alien-impactor (Alvarez_1980). The impact of the meteorite at the Chicxulub crater was so powerful that it generated a thermal-pulse strong enough to have ignited dry forest materials, contributing to global firestorms around the impact boundary that contributed to the Cretaceous-Paleogene extinction itself (Belcher_2015). The listener might not require its incidence in my resulting composition to be pointed out. I was drawn to mark out the contrast between the warm atmosphere of the Cretaceous with the global impact winter triggered by the meteorite collision.