Gravestones, Glaciers, and the Rate of Lichen Growth.

A student in Maine has learned that you can find out when a lichen colony became established on a fresh surface just by checking out the dates on gravestones and comparing them with the nature and size of the species on other gravestones with different dates. Join her and look at the back of the gravestones, and at any stones used to surround the graves. Lichens are also used to date lava flows and ancient human monuments. We were told by an elderly geologist that in his earlier years he used lichens as excellent indicators of glaciers' retreat. If you know how long it takes for lichens of a particular species to become established, and grow to the measured size, you can tell roughly when the rock became exposed, i.e. when the ice left it behind.

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