Video: Riddles of Sand and Ice Name Hour
Earth has experienced numerous changes in climate, some of them very extreme.
1. The last ice age covered much of and Europe.
2. Canada and New York both have giant that don’t match the bedrock.
3. Strange boulders that have been moved by ice are called .
4. In some places, the North American ice sheet was miles thick.
5. There have been up to ice ages in the last million years.
Today, the last of the great northern ice sheets is found in Greenland.
6. Greenland’s glaciers flow to the coast, break free, and end up as .
7. Most of central Greenland has been pushed down and out by the ice.
It takes a long time for snow to form a glacier.
8. Firn is packed snow that’s being slowly compressed into .
9. Dust marks the top of each year’s of snow.
10. As you go deeper into a glacier, ice crystals have grown .
11. Air pockets get .
12. When the ice is deep enough, pressure causes glacial ice to .
The Mendenhall Glacier of Alaska has been carefully studied for many years.
13. Sand and gravel at the end of a glacier are called terminal moraines.
14. The moraines show that the Mendenhall Glacier has recently .
15. The Mendenhall Glacier flows about per day.
16. photography shows the actual flow and movement of the ice.
Right now we’re in a time between ice ages (an interglacial) with glaciers rapidly retreating.
17. Grooves in bedrock show of movement during the ice age.
18. The glaciers also gouged out many . (including here in Minnesota)
19. We can follow the grooves northward to find out where the glacier .
20. The great ice sheets formed and flowed out of .
21. We know the glaciers were there because of the -shaped valleys they left behind.
We are just beginning to understand some of the things that may cause ice ages.
22. Earth’s changes from circular to elliptical and back again.
23. The of Earth’s axis also changes over time.
24. Ice ages were triggered more by summers than by cold winters.
25. As more and more snow accumulates, it reflects radiation back into space.
26. At one time, of Earth’s land was covered by ice.
Ice age climate change affected the entire Earth, even the Sahara Desert.
27. Tassili N’Ajjer means plateau of rivers.
28. Space shuttle radar confirms that the Sahara once had many systems.
29. Rock paintings from long ago show herdsmen tending in the Sahara.
30. As it became drier, rock paintings show instead of cattle.
31. Changes in tilt and orbit cause the locations of Earth’s to change.
(Plate tectonics also causes climate change, but over a much longer time span than ice ages. )
Conditions at the edge of the desert fluctuate widely. There may be severe drought and, in
some places, the desert is spreading. Many people live in poverty as refugees.
32. At the time of the film, Lake Chad was very rapidly.
33. Between 1973 and 1984 the lake shrank to of its former size.
Today, there are two contradictory forces at work on Earth’s climate.
34. Right now, natural cycles should cause Earth to get .
35. Human activity may cause the Earth to get .
The surface of the Earth is always changing but, today, . . .
36. for the first time, may have become a global force for climate change.
Research since the time of this film indicates that climate change may occur more rapidly than
was once thought possible. There is evidence of severe natural fluctuations within a single
human lifespan. In spite of new discoveries, we still don't know what "normal" climate is like.
There are so many variables at work that climate change is impossible to predict.