1 Greenhouse Earth 鄭琦翰

2 outline Examine the greenhouse world and evaluate explanations for its warmth Explore the reasons why sea level 100 Myr ago was some 200 meters higher than it is today Evaluate the effects of high sea level on climate Investigate the climatic and environmental effect of the impact of a giant asteroid that collided with Earth 65 Myr ago

3 What explains greenhouse warmth 100 Myr ago Around 175 Myr ago, the giant continent of Pangaea began to break apart By 100 Myr ago, most of the present-day continents had separated from one another

4 Cretaceous

5 It is the most recent example in the geologic record of a greenhouse world

6 Model simulation of greenhouse world Model:GCMs Data:past distribution of animals and vegetation,as well as geochemical evidence

7 Model:changes in geography(landsea distribution and mountain elevation ) Model:changes in geography and CO 2CO 2

8 The effect of CO 2 on climate

9 What explains the data-model mismatch Possible problems with the data Possible problems with the models Ocean

10 What explains the data-model mismatch Ocean (1)ocean heat transport hypothesis1)ocean heat transport hypothesis (2)Today,most of the deep ocean receives water from just two polar source areas2)Today,most of the deep ocean receives water from just two polar source areas (3)The deep ocean 100 Myr ago was filled with warm saline deep water formed in the tropics and subtropics3)The deep ocean 100 Myr ago was filled with warm saline deep water formed in the tropics and subtropics

11 A different way of forming deep water All the deep water that fills the ocean basins today forms in two cold polar regions

12 A different way of forming deep water 100Myr ago more of it may have formed in shallow,salty subtropical seas

13 What explains the data-model mismatch

14 Sea level changes and climate

15 We ignore these local effects on sea level and focus on eustatic change — changes that are global scale Since 80 million years ago, sea level has fallen from this long-tern maximum to its modern position

16 Causes of tectonic-scale changes in sea level Tectonically driven changes in the volume of the ocean basins and their capacity to hold water changes in volume of ocean ridges collision of continents construction of volcanic plateaus in the ocean Changes in the volume of water in the ocean as a result of changes in climate 4.water stored in ice sheets 5.thermal contraction of seawater

17 1. Changes in volume of ocean ridges

18 Ridge depth=2500m+350(crustal age) 1/2 (in meters) (at 0 age) (in Myr)

19 2. Collision of continents

20 3. Construction of volcanic plateaus in the ocean

21 4. Water stored in ice sheets: Today, the Antarctic and Greenland whose ice sheets have extracted a volume of ocean water equivalent to 72 meters of global sea level 5. Thermal contraction of seawater: The contraction of seawater caused by this cooling has reduced global sea level by roughly 7 meters

22 Sea level adjustment

23 Effect of sea level change on climate For large global sea level changes, the synchronous invasion and withdrawal of the sea on many continents should result in simultaneous fluctuations between harsh continental and mild maritime climates in many regions around the world High sea levels should cause cooler, more maritime summers that favor the persistence of snow and ice through the summer ablation season at very high latitude, but none occurred

24 Asteroid impact The geologic evidence for this impact includes the worldwide distribution of a thin layer of sediment enriched in iridium(Ir),an element that is rare on Earth but times more abundant in some kinds of meteorites The geologic evidence for this impact includes the worldwide distribution of a thin layer of sediment enriched in iridium(Ir),an element that is rare on Earth but times more abundant in some kinds of meteorites Other evidence for an impact event includes small grains of quartz with distinctive textures called “shock lamellae” that are formed by the shock wave of sudden pressures much larger than those found on earth,even in highly explosive volcanoes Other evidence for an impact event includes small grains of quartz with distinctive textures called “shock lamellae” that are formed by the shock wave of sudden pressures much larger than those found on earth,even in highly explosive volcanoes

25 Asteroid impact

26 Asteroid impact

27 Asteroid impact