Lecture 3 Flashcards
What can causes a change in surface level of the earth
Magma chambers can expand and contract, especially around eruptions and this can change the level of the surface surrouning
What can cause shorelines to change quickly
Earthquakes
What can cause global sea level change
Growth and decline of ice sheets. Between 15,000 and 6,000 years the sea level rose roughly 120m
What period of ice are we in
Interglacial
Interglacials
period of time with little ice
Glacials
Periods with more ice and lower sea levels
What is a pile of boulders left by glaciers
Boulder clay, or till
How do glaciers cause striations
drags rocks along and cause drag marks
What shape is common in boulder clay?
Triangular
Two types of foraminifera
(forams)
And why they are useful
- Planktonic—>shallow seas
- Benthic—>ocean floor
typically <1mm in size and are useful paleoenvironment indicators
But better is that CaCO3 shells contain record of oxygen composition of sea water
Oxygen isotope ratio use
18 and 16 are the main two stable isotopes of oxygen and the ratio can tell if more or less ice on earth.
16 is lighter and 500 times more abundant and evaporates more easily from sea water
Permanent ice caps exist then sea water increased 18 as the evaporated 16 stored in ice
What also affects the ratio in foraminifera?
Temperature as they take up more 18 when its cold.
This is an example of biological fractionation
How to get around the problem of temperature affecting ratio?
Use benthic as ocean floor has smaller variation in temperature and so the ratio is mainly affected by ice levels
Which three scientists in 1976 made a breakthrough in explaining the causes of the isotope variation?
Hays
Imbrie
Shackleton
What prediction did the pattern of climate variation follow?
Milankovitch in 1941
Who used celestial mechanics
What are the three main orbital effects?
- Eccentricity (the elliptical orbit changes by 6% over 100,000 year period)
- Tilt/Obliquity (orbital plane varies between 21.8 and 24.4 degrees-affects distribution of solar energy)
- Precession (Earth’s axis wobbles like a spinning top with a period of 22,000 years)
These aren’t completely accurate (the prediction from the three orbital effects) WHY?
Because of other climate variations
Like Albedo feedback where ice reflects more energy so causes it to get colder
or positioning of the movement in the oceans as movement of equitorial water (warmer) to poles
What is a drop rock?
A rock that icebergs have dropped onto the sea floor when they melt
Indicators and analysis of what features can tell the ages of previous ice ages?
x 4
Glacial striations
Varves
Drop-stones
Boulder clays
Ice ages are rare when where the last three?
- 260-270 Ma
- 410-440 Ma
- 1000-600 Ma
