1. The Cenozoic Era
Geology 103

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

3. Zuni transgression ends; Tejas begins

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

5. 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

6. Climate story of the Cenozoic is cooling

7. Grasses, a flowering plant, flourish as the climate cools

8. 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

9. 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

10. 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

11. 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

12. 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

13. 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

14. Evidence of Pleistocene glaciations