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RT @USGS_YES: Evidently it's #oldrockday, so here's a shot of some Precambrian rocks in the Black Hills of S. Dakota. And if you'd like to…
243 followers
RT @USGS_YES: Evidently it's #oldrockday, so here's a shot of some Precambrian rocks in the Black Hills of S. Dakota. And if you'd like to…
11,320 followers
RT @USGS_YES: Evidently it's #oldrockday, so here's a shot of some Precambrian rocks in the Black Hills of S. Dakota. And if you'd like to…
908 followers
Evidently it's #oldrockday, so here's a shot of some Precambrian rocks in the Black Hills of S. Dakota. And if you'd like to learn more about the geologic timescale, you can download a free geologic time bookmark here: https://t.co/CHnMmvh6MT Photo: J. Wi