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!

Friday, January 17, 2014

January 16. South American Cratons

By Richard I. Gibson

The cratonic core of South America is the Brazilian Shield, composed of Archean rocks modified by later tectonic events. The similar but smaller Guyana Shield occupies the northern part of the continent.

The two cratons are separated by the Amazon Rift – a long-standing break in what was probably originally a single large craton. That break follows a weak zone that has been around for hundreds of millions of years, and is the reason the Amazon River is where it is.

Map derived from U.S. Geological Survey

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