Can't really wrap my brain around stumbling upon 500 million year old rocks formerly wedged between the earth's mantle and crust. [also testing the preview function for articles that require a subscription - feeling *gneiss* might delete later]
Rare chunks of Earth’s mantle found exposed in Maryland
The set of rocks strewn throughout Baltimore likely represent a slice of prehistoric seafloor from a now-vanished ocean.
nationalgeographic.com