Exam 4

Why was early earth so warm?
combination of powerful greenhouse gases hihgh in co2 and ch4, as sun gradually brightened, co2 concentrations deminished
Negative feedback from chapter 8
between atmospheric co2 concentrations and the rate of silicate weathering
nearly massless particles emitted during nuclear reactions
solar wind
the sun losses some mass by way of solar wind, and outflow of charged particles from the sun’s corona
Why were carbon dioxide levels much higher during early earth?
impact degassing of late arriving planetesimals, along with enhanced volcanism on the hot young earth, however, weathering of finely dispersed ejecta could have drawn down levels
3.8 Billion years ago
presence of liquid and water suggests levels of co2. If earths solar temperature were lower as a result of low solar luminosity, the rate of silicate weathering should have been slower, lovering the co2 loss rate. Co2 emitted from volcanos would have accumulated in the atmosphere until the global rate of silicate weathering balanced the volcanic outgassing rate. Therefore, the earth has a natural way of recovering from global glacation
Anti-greenhouse efffect
absorption of sunlight by methane and organic haze, this cools earth
The long term climate record
earths climate on long time scales is that it has remained conducive to the presence of life for about 4 billion years
past climate, long periods of warmth seperated by shorter periods of intense cold
Phanerozoic Era
past 540 million years, scientists study fossil records
Hurion glacation
named after deposits first identified near lake huron, hurion glacation was followed by over 1 billion years of ice-free conditions during the late paleoproterozoic and mesoproterozoic
Why did earth go into the herion glacation
the rise of atmospheric o2 around 2.3 billion years ago would have eliminated most of the methane throwing climate into a temporary deep-freeze
Low latitude glacation
late proterozoic, between .8 and .6 billion years ago was so cold that it s considered a great mystery, evidence of glacation found on six of the seven continents
How would a snowball earth glacation proceed?

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

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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?


10 million years later volcanic outgassing rates reached .1 bar, melting the ice, the positive ice-aledo feedback loop begun to work in the opposite direction, became very hot with high co2 levels and low albedo
Pleistoncene Glacation
to qualify as a long term glacial period ice needs to be present on only some of earths continents for long periods of time. We are in this today, with antartica and greenland
co2 and climate during the paleozoic era

545 mya – 250 mya

climate cooled, due to decrease in atmosphereic co2 levels

Warm mesozoic era

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

sea floor spreading

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

ridges of sediment that are depostited at the front and sides of the ice sheets, when the ice melts, these ridges are left behind, marking the fartheset advance of the ice sheet
of the past 700,000 years apprear to have occurred every 100,000 years. These cold intervals are seperated by warmer shorter intervals kown as interglacials – continental glacation is limited to antartica and greenland
Why does earths climate oscillate between glacial and interglacial states?

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)

Milanovitch Cycles

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

Orbital theory

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

change of earths orbit through time
mainkovitch says that the gravitational influence of the moon and the other planted combined with earths slightly nonsphereical shape induce small but important variations in earths orbital parameteres, triggering the onset and end of glacial intervals
obliquity varaiations
obliquity varies from 22 to 24.5 every 41,000 years. The warmth of summers and coldness of winters is increased by higher obiquities
eccentricity variation
varies periodicaly between 0 and .06, current value being .017. cycles are about 100,000 and 400,000 years
ice-albedo feedbacks
any change in the seasonal distribution of solar luminosity that affects the growth of ice during the winter or the meltback during the summer has the potential to affect the planetary albedo
vostok ice core
scientists first discovered that the ice contained air bubbles frozen into the glacier as it grew
feedback affecting atmosphereic co2 on glacial time scales

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

Role of the biological pump

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

Shelf nutrient hypothesis
as glaciers grew, sea level feell, espocing the vst, low-relief margins of the continents. sediments of the continental shelves ae rich in organic matter an dnutrients as the result of th ehihgly productive nature of the overlying waters. With these being exposed, weathering reactions release ht nutrients to the rivers draining the shelves. This enchanced phosphate tot he oceans causing an increase in marine productivity and a drop in atmospheric co2. created a positive feedback loop/ response time is 40,000 to 100,000 matching the periodicity of glacial-interglacial cycles. 
iron fertilization hypothesis
increase flux of dust to the oceans during glactial times
coral reef hypothesis
as organisms grow, they add to the rock framework building laterally as well as vertically until the water surface is reached. the growth f coral reefs seres as an additional source of carbon dioxie to the atmoshpere. When ancient reefs are exposed by a drop in seal level, chemical weathering leads to their dissolution. This is the reverse of the reef growth. the growth and destruciton of coral reefs can affect atmosphereic co2 on glacial-interglacial times scales
Changes in terrestrial biomass
negative feedback loop – the amount of terrestrial biomass was drastically reduced during the last glacial interval. the growth of the terrestrial biomass during deglaciaiton and its destruction during the initiation of a glacial interval represent th only negative feedbacks to atmospheric co2 changes on glacial timesclaes
last major continental glaciation

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 principle that processes operating today also operated in the past, and that past geologic events can be explained in terms of processes active today

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

The holocene
relatively small changes n the mean global temp are associated with relatively large changes in the physical environment
The younger dryas
earth began to warm between 10,000 and 15,000 years ago, temp levels almost perfectly matched by changes in atmosphereic co2, co2 changes caused by the shutting down oft f the thermohaline circulation in the north atlantic
The holocene climatic opimu
the short cold interval of th e younger drays even eneded with a rapid shift to warmer conditions followed by a constant climate warming over the next several thousand yeas. This suggests that tsummer temps were slightely higher 5-6 thousand years ago than as of recent. 
The medeval warm period
temps fells after the holocense climatic optimum reachinga  min about 3,000 years ago, but recently rose to a new maximum.
The little ice age
interval of cooling from medeval to the early 1500s. characterized by considerable variability
volcanoes and the climate
volcanic ash aggregates very quickly and falls out of the atmosphere with tens to hundred of kilometers of the eruption. sulfur dioxide gas oxidizes forming sulfuric acid, this reflects solar radiation, resulting in a warming of the stratoshere. lasts only 1-2 years after eruption
an increase in the abundance of sunspots, which are cooler areas on the suns surface, corresponds with an increase in the amount of solar radiation earth receives. Sun is actually slightly brighter during periods when sunspots increase.
sunspot levels
mid-lattude glaciers advanced and termps fellwhen sunspot snumbers were low and taht temps increaed and glaciers retreated when sunspot numbers were high
climate system regulated by
silicae weathering, plate tectonics, and changes in atmospheric composition
climate changes on time scales of hundreds of thousands of years
associated with atmospheric composition, earths orbit around the sun, ad changes in the extend of large ice sheets
T or F: During periods of cold climate (ice ages), oceanic organisms have a greater tendency to incorporate the heavy isotope of oxygen, 18O, into their calicum carbonate skeletons/shells.
el nino
used to describe a major shift in the oceanic circultion that occurs every 2 to 10 years
Gouging of bedrock by pebbles and rocks frozen onto the base of an advancing glacier, formation of moranis by bulldozing action of an advancing glacier, formation of till, and formation of loess(fine grained sediment produced by glacial abrasion, are all geological evidence of what?
Glaciation events
two consequences of the el nino southern osillation events

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

T or F: it is believed that the first glaciation on the earth occurred about 2.3 bill years agaon when atmospheric oxygen levels rose causing atmospheric methan to drop abruptly. 


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


The Huronian (2.5 bill yrs ago) glaciation was caused by _____?
A decrase in methane due to rise of oxygen
late proterozoic

snowball earth -completely froze over. The sun 

was 6% less bright. It is 

estimated that CO 

2would need 

to be ~560 ppm(assuming low 


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 



The late proterozoic (750-600 mill years ago) glaciation period was casued by?
the draw down of CO2 by increased carbon burial on new continental shelvves and silicate weatheing of a large continental mass located near the equator.

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)

The permocarboniferous period (286 mill. years ago) glaciaiton was caused by?
The doubling of the organic carbon burial rate as a result of the formation of large coal beds

 (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! 

The glaciation during the Pleistocene (1.8 mil to 20,000 years ago) was most likely caused by?
Fluctuations in CO2 that correlate with variations in earths orbit and solar illuminaiton in the northern hemisphere summer
after mesozoic

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 


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

During periods of cold climate (‘ice ages’), oceanic organisms have a greater tendency to incorporate the heavy isotope of oxygen, 18O, into their calcium carbonate skeletons/shells.

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

C. massive biomass buring
First glaciation period
T or F: during warmer periods know as interglacials, even greenlan become ice-free, leaving Antarctica as the only major land-mass with an ice sheet.
Geologists who have studied the long-term glacial record have concluded that earths climate history has been market by _______ main periods of glaication.

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


200-280 ppm
T or F: Between 0 AD and 1900 AD, Earths global mean temperature varied by no more than 1.5 degrees C.
T or F: If the biological pump were to stop completely, the abundance of CO2 in the atmosphere would increase to about 720 ppm.
T or F: Based on continuous measurements of CO2 from Mauna Loa, Hawaii, present day abundances of CO2 in the earths’ atmosphere are over 370 ppm and rising steadily every year since the measurements were started in 1957.
Ice core data from greenland reveal the beginning about 15,000 years ago, when the earth was coming out of the last ice age, very large changes in cliate occurred over very short timescales. How short were these timescales?
about a decade or less