Transcript Week 7 Climate Change Presentation Week 7 Cretaceous and

Week 7 Cretaceous and Snowball
Earth
Past climates – why bother?
Cretaceous
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What was it like?
How did the geography differ?
How can we assess past climates
What caused the climate to be so different?
What do we know about the
Cretaceous?
Some context
• Billion = thousand million = 1,000,000,000 =
• 1 x 109
• Earth is 4.54 billion years old
• Life started around 3.8 billion years
• Early man Homo habilis evolved around 2
million years
Greenhouse and icehouse
Cretaceous
Starts: 150 Million years ago
Ends: 65 million years ago
Chicxulub
Late Jurassic/early Cretaceous
geography
Late Cretaceous geography
Movement of the continents
Plate tectonics video
Carbon cycle
Ocean currents
What was the Cretaceous climate like?
Cretaceous land masses
http://www.palaeogeography.net/palaeoclimatology/climate_change/clim_change.
html Paul’s Paleopages
Evidence from the Arctic
Arctic today
San Joachim Delta - California
Cretaceous - dinosaur weather
http://www.dailymail.co.uk/sciencetech/article-2523106/The-dinosaur-lookedlike-CHICKEN-Edmontosaurus-fleshy-rooster-comb-beak-like-mouth.html 3 July
2015
Rain
No Mount Everest
Swamps, mires, bogs
Arid Equator, no rainforests
Cretaceous flora and fauna
How can we assess the climate in the
past?
Proxies for climate - fossils
Nilssonia
Modern cycad
First flowering plant: Archaeofructus
Hadrosaur footprints
Polar light regime
Warm shallow seas
Raised coral reefs – Huon Peninsula
Proxies for climate – volcanic activity
Mount Pinatubo
Gases emitted by volcanoes
Greenhouse gases
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Water
Carbon dioxide
Methane
Ozone
Nitrous oxide (NO)
Chlorofluorocarbon (CFC)
Hydrofluorocarbon (HFC)
Sulfur Dioxide
Flood basalts
Deccan Traps
Cretaceous
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Warmest period in Earth’s history
High levels of CO2 – intense volcanic activity
Different geography
Fossils of warm adapted animals and plants
A few degrees at Equator but 20 degrees C
North Pole and degrees 40 C at South Pole
• No icecaps
Snowball Earth
Joe Kirschvink
http://www.snowballearth.org/
Snowball Earth
• Hypothesis – not all scientists agree
• Planet Earth covered by ice from pole to pole
• Milankovitch cycles – variations in axis and
orbit
• Low levels of greenhouse gases
• Position of continents
• Positive feedback mechanism
• http://snowballearth.org/
What evidence might we look for to confirm the
Snowball Earth theory?
Traces of glacial rocks
Glacial striations
Distribution of glacial rocks
Calculating CO2
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Estimates of weathering
River run-off
Land elevation
Biological activity
Volcanic activity
Tested against geological sources from ice
cores
Milankovitch cycles
•Wobbles in axis and
orbit
•Axial precession
•Apsidal precession
Albedo
Positive feedback
Weathering
Where will it rain most?
Where will it rain most?
Key ingredient for weathering
Silicate weathering
Silicate rock + Carbon Dioxide + Water
Calcium ions + Hydrogen carbonate + Silicon
Dioxide
What ended Snowball Earth?
Increased biodiversity
Cambrian explosion
Why study past climates?
Earth’s energy balance
What is energy?
Energy definition
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You can’t see it
You know when it’s there (or not)
It can’t be created or destroyed
It can change from one form to another
Energy is a physical property
It’s a measure of the ability of the object to
“make things happen”
Energy
Energy
From the sun
• 1.74 x1017 Watts
Human population 100 Watts per person
1.0 x 1011
Energy from the sun is million times higher
Week 6 Past Climates
Checking for reliability
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Where does the information come from?
Where was it published?
When was it published?
Does the author or publication have an
agenda?
• Are there references?
• Where can you get more information?
Greenhouse and icehouse
Plate tectonics