Glacial grooves

 

What are the oldest phonograph recordings in North America? Here's a hint: they predate Thomas Edison's "Mary Had a Little Lamb" (1877) by at least 12,000 years.

During the Wisconsin Glacial Episode,[1] rock fragments carried along by the mile-thick ice sheet carved countless miles of linear grooves, or striae, into the hard bedrock. When the ice finally retreated about 12,000 years ago, it left behind a storehouse of planetary knowledge encoded in the bedrock grooves that are now visible all across North America. How do we listen to these recordings? And what messages do they contain?

The first step, of course, is to build a pickup. The diamond- or sapphire-tipped needles of a vinyl phonograph player are much too fine for this purpose. But a small hand-held piece of granite works well. Simply attach a pair of piezoelectric transducers, arranged orthogonally so as to capture the independent vertical and lateral components of the rock's motion and — voilà — you have a glacial stereo pickup. All that's left is to plug the pickup into a sound recorder and pull the pickup along a groove at a steady pace...

long

Playing the rock (here, a basaltic intrusion into the granite basement).

closeup2

Closeup of stereo pickup, made of local pink granite.


Note

1.
See "Wisconsin Glaciation" in Wikipedia