The Cenozoic Era Geology 103

What periods are in the Cenozoic? The basic problem is that there aren’t many “big” mass extinctions in this era!

Zuni transgression ends; Tejas begins

Antarctica separates from Australia, heads to the South Pole (Eocene)

Eocene thermal maximum Around 55 my ago, temperatures worldwide increased to levels similar to the early Mesozoic Cause is uncertain, but may have involved increased atmospheric methane due to warming of ocean floor releasing methane from methane clathrates Caused many reptilian and mammalian orders to go extinct

Climate story of the Cenozoic is cooling

Grasses, a flowering plant, flourish as the climate cools

One adaptation: a new type of photosynthesis Prior to the Eocene, plants used a form of photosynthesis called C3. During the Oligocene, as a response to lowering CO2 levels, drought conditions and other environmental stresses, some plants developed C4 photosynthesis, which concentrates CO2. Arose in many families of plants simultaneously; a good example of convergent evolution One adaptation: a new type of photosynthesis

Himalayan orogeny occurs in Pliocene and continues today India detaches from Gondwana and heads north Collides with Asia about 10 my at a (tectonically) rapid rate Raises Himalayas, Tibetan Plateau, Tien Shan Causes northern subtropical jet stream to split around the uplift, and repositions the high and low pressure areas over the Pacific

Cenozoic climate trend is drier 5.96 my – Strait of Gibraltar closes 5.96 – 5.33 my – Messinian salinity crisis 5.33 my – Zanclean flood event

Closing of Panama isthmus Subduction-related volcanism closes isthmus about 3 my Allowed ice sheets in Northern hemisphere to form More salty water in Atlantic Water sinks because it cools as it heads north Releases heat as it sinks, so polar oceans never get warmer water

Ice ages start up about 2 my ago Why then? Several factors need to be in place: polar continent, north/south-oriented oceans, split in the sub-tropical jet stream At that point, subtle factors can determine whether the glaciers build up or not

Milankovitch cycles Milutin Milankovitch (University of Belgrade, Serbia) proposes that “orbital parameters” that vary in a cyclic fashion over tens of thousands of years will determine that amount of solar insolation that reaches the Earth’s surface

Evidence of Pleistocene glaciations