a large fraction of the continental area wa situated in teh tropics, this allowed silicate weathering to process even though the earth was growing colder so that atmosphereic co2 could contine to be drawn down. Global glacations require continents at low latitudes

As atmospheric co2 levels declined, the polar ice sheets gradually crept down tot lower latitudes, within a few decades the oceans froze all the way tot the equator. 

How did we get out of the global glacation?

545 mya - 250 mya

climate cooled, due to decrease in atmosphereic co2 levels

the age of the dinasaurs, past 251 my

-because large animals lived during this period is warm

- the measurement of oxygen isotope ratios in carbonate sediments were recoverd from deep-sea cores

faster spreading rates led to fastter rates of subduction of carbonate sediments with leds to increased levels of co2

- part of why the mesozoic period was warm

1. change in the degree to which earths orbit around the sun is elliptical (eccentricity)

2. Changes in the tilt of earths spin axis with respect to the plane of its orbit around the sun (obliquity)

3. changes in the orientation of the spin axis with respect to earth's orbit (precession)

The critical factor for northeren hemisphere continental glaciation was the amount fo summertime insolation at high northern latitudes

- high insolation leads to warmer summers, and the winter snow pack melts (today)

- low insolation the snowpack would survive over the summer allowing snow and ice to accumulate and an ice sheet to form

because planetary orbits are eccentric, earth is clower to the sun at some time of the year than at others.

- the point of closest approach is called perihelion

-the point of maximum distance from the sun is called aphelion

- Northeren hemisphere winters are milder than southern hemisphere winters and somewhat shorter

its spin axis is tilted 23.5 degrees from teh perpendicular to the plane of its orbit. Obliquity creates the contrast between the seasons. Without obliquity, winter and summer would be very similar

- seasonal contrast is slightly bigger in the southern hemisphere than the northern hemisphere

on lpng time scales te carbonate siliate geochemical cycle, together with the weathering anddepsostiton of organic carbon ridch sedimentary rocks, determines the steady state atmosphereic co2 level. 

- Also, the partitioning of carbon between the atmosphere and terrestiral biomass, and between the atmosphere and ocean as affected by the oceanic biological pump are of great importance to the co2 balance during glacial cycles

if the biological pump were 100% efficientin removing nutrients and co2 from surface waters, the atmosphereice co2 pressure would be reduced to about 165 ppm. 

- If the biological pump ceased completely, teh atmospheric co2 level would rise to about 720 ppm as the co2 charged deep waters mixed with the surface waters and homogenize the chemical compostion of the ocean

reached maximum extent about 21,000 years ago

- the interval from the last glacial retreat to the present is referred to as the holocene

the study of pollen and organic misctofossiles

- can construct the plant assembleges from long ago

the method of dating trees by counting their annual growth rings

- amount of growth can be related tot he temp during the growing season or to water availability

1. it shifts the pool of high sea-surface temps from the west to the central pacific, whichn then completely changes the atmosphereic ciruculation. 

2. it shuts off the upwelling on te eastern pacific which has drastic consequences fro biological productivity. The loss of nutrient rich water leads to a massive die back of marine organisms and the bird life that feeds them

2300-2500 mya –removal of methane from the 

atmosphere due to rise of oxygen dramatically reduced the 

greenhouse effect followed by 1 billion years of iceless

snowball earth -completely froze over. The sun 

was 6% less bright. It is 

estimated that CO 

2would need 

to be ~560 ppm(assuming low 

CH 

4) or larger to keep Earth ice- 

free.  The continents were all 

grouped at equator at this time, 

so there was significant 

weathering of continents even as 

ice built up at the poles (on 

ocean) pulled down the CO 

2- 

ice/albedofeedback!

Late Ordovician and Permo-Carboniferous

440 mya and 286 mya

organic carbon burial lowered

Then, it was warm for 250 million years as Pangaea broke up, 

and sea-floor spreading led to increased CO 2 in the 

atmosphere.  For a long period of time, there was high CO 2

(4x today’s values)  (p 245)

 (251-65 mya) so warm? This is when 

Pangaea started to break up, and sea-floor spreading would have 

been significant, leading to release of CO 

2to the atmosphere, and 

a strong greenhouse effect. Deep ocean temperatures during the 

Mesozoic were 15 oC! 

Then, about 80 mya, Earth started to cool, maybe due to a slow- 

down of sea-floor spreading. 30 myathe cooling accelerated, 

perhaps due to the collision of India with Asia, forming the 

Himalayas, which, as they weathered, enhanced the removal of 

CO 

2from the atmosphere. (p 249)

1.8 mya-10,000 ya(Chapter 14). The 

fifth “ice age” heralds a new era of glaciations that are 

timed closely to changes in Earth’s orbit –Glacials(cold 

periods) and interglacials(warm periods) are an example of 

a two-state climate system

Which of the following is probably not a likely cause of a major ice age?

a. reduced solar illumination in the norther hemisphere.

B. reduced methane from reaction with oxygen

C. massive biomass buring

D. Increased organic carbon burial

E. Increased weathering of rocks

Over the past 400,000 years ( and before 1900) atmospheric CO2 abundances have flucturated between what two values?