Goals for this section 1.EXPLAIN the feedback mechanism believed to have maintained Earth's average temperature within the range of liquid water over 100s of millions of years, as the Sun got brighter. 2.Based on albedo, solar radiation, and atmospheric gases, CONSTRUCT logical chains of events that would result in major glaciations or warm periods on Earth. 3.IDENTIFY and EXPLAIN the primary trends and climate events of the past 65 million years based on oxygen isotope data. Long-Term Climate Evolution: Quiz 5: Nov 30-Dec 1 Final review is Dec 4: Submit Qs on Discussion Board

RELEVANCE

4.5 billion years ago – Earth forms billion years ago – Huronian glaciations million years ago – Snowball Earth WARM What next? More ICE SNOWBALL EARTH

Ice in Australia, which was then at the equator Evidence for Snowball Earth

Clicker Question: How could having all continents bundled near the equator help trigger a global glaciation? A.The continents must have had high mountains where glaciers could form B.Warm temperatures in the tropics would keep silicate weathering rates high C.There would be less volcanism if all the continents were in the tropics D.The poles could freeze more easily if they were water-covered E.All of the above

Magnetic minerals in volcanic rocks formed in Australia during Snowball Earth are horizontal  Australia was close to the equator Evidence for Snowball Earth Notes

Getting into Snowball Earth Continents at low latitudes   chem weathering   CO2  colder Ice expansion   albedo  runaway ice-albedo feedback  SNOWBALL Hoffman & Schrag

Clicker question: What’s the most likely factor to help Earth escape from the “snowball” scenario? A. Increased burial of organic carbon (e.g. coal deposits) B. Increased solar output C. Lower sea level D. Volcanic activity E. Biological production of oxygen

Escape from Snowball Earth Tectonics & volcanism   CO2 Hoffman & Schrag Ice cover prevents chem weathering   CO2 even more…  greenhouse finally gets strong enough to melt ice  ice-albedo feedback

Clicker question: Once the ice sheets starting melting, more land surface was exposed. What kind of feedback loop between ice and albedo would be triggered as the Earth came out of the Snowball scenario? A. Positive feedback loop B. Negative feedback loop C. Neither D. Both

million years ago – Permo-Carboniferous glaciations 4.5 billion years ago – Earth forms billion years ago – Huronian glaciations million years ago – Snowball Earth WARM Warm again, cold again… WARM

Clicker question: The Permo-Carboniferous glaciations happened when all the continents were together in the supercontinent Pangaea. What effect would the process of assembling a supercontinent have on greenhouse gas concentrations? Greenhouse gases would ______. A. Increase B. Decrease C. Stay the same

COLD! Decreased atmospheric CO 2 as Pangaea formed Causes of the P-C glaciations

Formation of coal deposits

ICE COAL DEPOSITS Ice cover during the P-C glaciations

Clicker question: Why didn’t the Earth turn into a snowball this time? A. As the continental ice sheets grew, sea level fell. B. Glaciers excavated the new swamp deposits. C. Ice cover on polar continents decreased silicate weathering. D. Swamps output additional oxygen.

4.5 billion years ago – Earth forms billion years ago – Huronian glaciations million years ago – Snowball Earth WARM Warm again, cold again, warm again… WARM million years ago – Permo-Carboniferous glaciations WARM

Pangaea was breaking apart Higher rates of seafloor spreading Increased CO 2 from volcanoes Causes of the post-glacial warming

4.5 billion years ago – Earth forms billion years ago – Huronian glaciations million years ago – Snowball Earth WARM Finally, the past 65 million years WARM million years ago – Permo-Carboniferous glaciations WARM Last 2.5 million years – Pleistocene glaciations X No more dinos! Million years ago LOW  “Temperature”  HIGH

Warming prior to 50 Ma Million years ago LOW  “Temperature”  HIGH Subduction of carbon-rich sediments under Asia Warming

Cooling after 50 Ma Million years ago LOW  “Temperature”  HIGH Collision produced mountains and increased chemical weathering Long-term cooling

Benthic Forams: CaCO 3 Estimating past temperatures Ocean Sediments Deep ocean temperature  18 O For an ICE-FREE WORLD

? ? H 2 18 O H 2 16 O Distillation of water  Fractionation of oxygen isotopes H 2 16 O (light) & H 2 18 O (heavy) H 2 16 O

? Clicker Q: How would the oxygen isotopic composition of the water in an ice sheet compare to the oxygen isotopic composition of ocean water during an ice age? A.Ice would be heavier than ocean B.Ice would be lighter than ocean C.Ice would be the same as ocean ?

16 O “lighter” 18 O “heavier” H 2 16 O H 2 18 O H 2 16 O Evidence: Distillation of water  Fractionation of oxygen isotopes 16 O (light) & 18 O (heavy)  Sea level  Ice sheet size

Temperature or 18 O in the ocean  18 O in the shells Foraminifera: CaCO 3 CaC 16 O 16 O 16 O CaC 16 O 16 O 18 O CaC 16 O 18 O 18 O lighter heavier [ ]  18 O = 18 O/ 16 O sample 18 O/ 16 O standard * 1000  18 O/ 16 O measured in shells Higher  18 O  colder water temperatures (and/or more ice) Lower  18 O  warmer water temperatures (and/or less ice)

Estimates of past temperatures

Who’s driving? Total “forcing” based on temperature estimates Changes in solar radiation and albedo Changes in greenhouse gases Pleistocene Glaciations

Causes of the Pleistocene glaciations: India-Asia collision – decreased greenhouse Ice-albedo feedbacks once ice formed on Antarctica

Summary: Long-term Climate Evolution The “faint young Sun” paradox can be resolved by higher greenhouse gas concentrations in Earth’s early atmosphere. Each of the 4 major glacial periods in Earth’s history occurred under different circumstances with different perturbations and feedbacks (construct the logical chains of events for each): Huronian – rise of atmospheric oxygen, drawing down methane Snowball Earth – continents in tropics, high weathering rates, ice-albedo feedbacks Permo-Carboniferous – mountain building and organic carbon burial Pleistocene – mountain building (Himalayas), then ice- albedo feedbacks Oxygen isotope records from the past 65 My record temperature changes that help resolve the three main climate driving forces in this period – the Sun, albedo, and greenhouse.