Why does earth periodically experience an ice age?

Question

Why does earth periodically experience an ice age?

Answer 1

if earth doesn't have a period where it can "cleanse itself", then it wouldn't be able to support life after a while. a time will probably come for another ice age caused by a meteor 1.5+ miles in size.  

Answer 2

I don't think earth ever had a real Ice Age. Only a big gigantic flood that even covered the very tips of the mountains. Only 8 people survived

Answer 3

Ice ages come from a variety of causes. The "Little Ice Age" that occurred in the 1300-1800s was likely due in part to a decrease in sunspot activity as well as an increase in volcanic activity.

The Younger Dryas event that occur ed about 12,000 years ago was more complicated and less understood. What is known is that the thermo-haline cycle shut down the ocean current conveyor belt that allows warm water from the equator to move north and cooler air from the poles to return to the equator. The cycle shut down because of North America's deglaciation which lead to a giant dam of water bursting in the area known today as The Great Lakes, changing the salinity of the water and forcing the warm ocean currents far underwater.

The earth heats and cools from a mixture of volcanic influence, asteroid and comet impacts and sunspot activity and recently human induced global warming as well.  

Answer 4

Solar cycles.  The Sun heats up and expands then cools off and shrinks.

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