but why does one strike make it cold and the next make it warm?
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Confusing right? The first event struck the ice cap in the vicinity of the Great Lakes an caused temps to plummet from all the fires whose as rose to make a long period of what we would call a “nuclear winter”.
The second, a 1000 year later, ended the Younger Dryas by possibly shattering a ice blockage of the Gulf Stream (this is just a scenario, as it cannot be proved at this time, but is a likely conjecture). Releasing the Gulf Stream warm ocean currents thawed the shores of the Atlantic as it does to this day
Looks like I have iggernunce to spare.
What fuel is there to burn when a comet strikes a continent-sized ice cap? Trees and other stuff that has been crushed under the ice?