17. Quaternary Period
The study of Pleistocene and the
Tertiary time may give us clue about the causes of previous glaciations also.
The causes of this glaciation has been studied in big details, and scientists are still working on this question.
of ice age
1. We all know, that nothing can start an ice age if there are no continents around the poles. If the location of the continents are close to the equator, there is no way to start to develop polar ice in sea water.
-Remember: to start polar ice, we need continent there, because it is easier to keep the snow there after winter (albedo).
-In sea water with the salt it is really hard to start ice, and the albedo also is much smaller, because the dark gray ocean can absorbe much more heat thans the white ice covered land.
2. Very important to check on the oceanic circulation. During supercontinent times, the one big continent can not develop local cold currents around the polar region.
In the ocean huge cold and warm currents form, and the seawater has much more equal temperature.
If the continents are broken up as they are today, local cold or warm currents can form, making the so called ice box. effect.
3. Important to know about the gravitational forces, which can influence global climate!!! (We have talked about before!!!) (Milankovitch Theory, 1920’s).
He calculated, that three parapmeters of the earth’s orbit has strong influence on the climate.
A. Eccentricity 100,000 k.y.
B. Obliquity 41,000 k.y.
C Precession of equinoxes 23,000 k.y.
The effect of precession causes the position of equinoxes to shift slowly around the earth’s elliptical orbit.
Continuous changes of these parameters cause the amount of solar heat recieved at any latitude to vary slightly over time.
Milankovitch proposed, that the
interaction of these parameters provides the triggering mechanism for the
glacial-interglatial episodes of the Pleistocene.
the Cenozoic glaciation
There are evidences that the climate on the earth was still warm and equable during the Eocene.
-The first dramatic cooling occured 37 million years ago, at the end of the Middle Eocene. This cooling occured in both land and oceans. (This cooling could be the cause of some of the extinction about this time).
-Abundant glacial deposits are evidence that Antarctica was partially glaciated during the early Oligocene. The earth average temperature dropped by 8° in less than a million years. At this time the annual temperature range grew from 10° in the Eocene to more than 20° in the Oligocene. The cooling and extreme temperature difference were occupied by drying.
-By the Middle Oligocene the
climatic deterioration had reached its low point. The major galtiation in
Antarctica has locked up huge amount water in the ice cap and caused a big drop
in sealevel, the largest one in the whole Cenozoic.
Opening passage between Australia and Antarctica allows cold water to circulate around Antarctica, turning it into a giant ice-box. Development of Circum Pacific current. No mixing with equatorial water!!!
However the development of this current happened in steps!!!!
1. Opening of shallow gulf between Australian and Antarctica provided enough moisture for the late Eocen ice developed on Antarctica,
2. By the Middle Oligocen there was a big glaciation on Antarctica.
3. During the early Miocene there was a warming period, and the glaciers in Antarctica disappeared, until, they come back at the end of the Miocene 15 millions years ago. This big cooling is related to the sinking of the iceland-Faerore bridge, which opened up the world ocean to the cold arctic water.
4. The next climatic even marks the Pliocene-Miocene boundary. This is again a big cooling, Antarctica ice grew. Lower sea-level, Mediterranean dried up!!! Gibraltar formed due to the collision between Africa and Europe. (6.3 million years ago).
5. During the Late Pliocene
there are already evidences for the Arctic ice cap. At tyhe same time glaciers
started to advance in the northern continents.
Quaternary period is divided
into two epoch, the Pleistocene and Holocene. Together they represent the last
1.6 million years of Earth’s history.
This time is extremly important
for us humans. Not only because our own
species Homo sapiens has evolved but Pleistocene was the time of the development of the huge ice sheets that advanced and retreated over
the land surface, directly or indirectly forming the present day morfology of
During the last 2 million years at least 20 major cold and warm period in the world. Strastigraphic evidences prove clearly 4 of them in North america, and six in Europe.
During the advances of the glaciers, the climate became more arid, sea level was much lower.
The climate belts were not
exactly the same as they are today, for example because of the presence of the
ice much farther south the Sahara was much more wet, than it is today.
The four glacial stages in north America:
The three interglatial stages are
100’s m sea level changeL blue holes in the Bahamas, Florida
Lots of tillite, loess so on...
How do we know, that there were 20.
For that the deep sea cores providing good evidences
Changes in sea level
Land bridges, drying mediterranean
Bering Straits between Alaska and Siberia
Steram erosion at sea level lows
Uplifting of the areas, which used to be under ice
Pluvial, proglacial lakes
Big rootles rocks