The 366 daily episodes in 2014 were chronological snapshots of earth history, beginning with the Precambrian in January and on to the Cenozoic in December. You can find them all in the index in the right sidebar. In 2015, the daily episodes for each month were assembled into monthly packages, and a few new episodes were posted. Now, the blog/podcast is on a weekly schedule with diverse topics, and the Facebook Page showcases photos on Mineral Monday and Fossil Friday. Thanks for your interest!

Wednesday, April 2, 2014

April 2. Silurian time

The Silurian Period as it is now defined spans the time from 443 million years ago – the end Ordovician extinction – to 416 million years ago. The error bars on those dates are a million or so years. The Silurian covers just 27 million years, the shortest period we’ve defined.

Where the Cambrian and Ordovician were more or less divided into early, middle, and late epochs, the Silurian has four major subdivisions: Llanderovy, Wenlock, Ludlow, and Přídolí. The first three are named for rocks found in Wales, Scotland, and England, respectively, and the Pridoli is from the Czech Republic. Each epoch is separated from the next by breaks in the rock record, some of which coincide with relatively small extinction events, but the real definition of the epochs is based on specific graptolite zones. You can hear more about graptolites in the podcast for March 8

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Charles J. Vitaliano, a geology professor at Indiana University, one of my own college professors, was born April 2, 1910, in New York City. He specialized in igneous and metamorphic rocks and mineralogy as well as field geology.

—Richard I. Gibson

Time column from Wikipedia

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