As they cascade downwards, they form discrete layers that can be preserved over geological time as laminations in the rock.

BBC: Curiosity Mars rover to investigate classic rock type

It is difficult for them to assess whether the melting being observed at the moment is unprecedented in the context of geological time.

BBC: Polar expedition to study Antarctica's climate history

Nor is there a geological shortage this time round.

ECONOMIST: A fundamental change is coming sooner than you might think

The first earthquake, with a magnitude of 6.4, hit Saturday at 4:53 p.m. local time, according to the U.S. Geological Survey, which said the epicenter was 23 kilometers (14 miles) southwest of Ahar.

CNN: More than 300 killed, 3,000 injured in Iran earthquakes

Archaeological evidence has the potential to reveal earthquake activity over millennial time spans, especially when integrated with historical documents and geological evidence.

UNESCO: Tales set in Stone: learning from ancient earthquakes

Geological faults do not necessarily produce earthquakes in a nice, linear fashion over time.

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The first earthquake, with a magnitude of 6.4, hit Saturday at 4:53 p.m. local time, 37 miles northeast of Tabriz, according to the U.S. Geological Survey, which measured 11 aftershocks.

CNN: Rescue operations end after Iran quakes kill 250