Expert: Ralph Salier - 11/25/2002

Question
Hi Ralph,

I have two questions, and I hope it's OK to ask you both together. Hope you can help!

1) When was the last Ice Age, and how long did it last?
2) How does carbon dating work?

Thank you in advance,
Richard

Answer
Carbon dating is done by looking at the ratio of "regular carbon" and "radio active carbon" in a sample from the last 50,000 years.  What happens is that in the atmosphere gamma radiation alters the regular carbon and it becomes heavier with the addition of neutrons.  This occurs on an ongoing basis so there is always a ratio of regular to radioactive carbon in the atmosphere.  This has been charted going back some 50K years.  Plants and animals breath in both kinds of carbon and plants and animals use both kinds of carbon in the same way so the ratio of regular carbon to radioactive carbon remains the same untill the death of the plant or animal.  Once this occurs the natrual decomposition of the radioactive carbon begins.  This means that the ratio of regular to radioactive carbon begins to alter.  Since the rate of decomposition is known and the relative ratios of radioactive to regular carbon is known over a long peroid of time, then a sample of carbon can be taken from plant or animal remains. The sample is then studied for this ratio and compaired to the charts of known ratios and anticipated age and from this a dating can be determined.

The last ice age ended some 12,ooo years ago (depending on several variables) and had lasted for some 100,000 years prior to the end.  There were several "interstadials" or periods of time when the ice retreated but these did not last long, only a few thousand years.  

I hope this answers your questions.