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 an occasional schedule with diverse topics, and the Facebook Page showcases photos on Mineral Monday and Fossil Friday. Thanks for your interest!

Thursday, January 16, 2014

January 11. The first redbeds



By Richard I. Gibson

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Transcript: Redbeds are sedimentary rocks such as sandstone, shale, and siltstone that contain enough oxidized iron, usually in the form of the mineral hematite, Fe2O3, to give the rock a reddish color. The fact that the iron is oxidized indicates that the sediments were exposed to oxygen-rich air or shallow, oxygenated water when they were deposited, and this in turn indicates that they probably formed on land or very shallow water such as lakes and ephemeral streams. Redbeds are associated with deserts in places.

In the book, I said that the oldest redbeds date to 2.6 billion years ago, but that’s incorrect. More recent work and better dating puts the oldest redbeds, the Jatulian rocks of Finland, at about 2.3 billion years old.

The age of the oldest redbeds can be used to infer the success of photosynthesis. By 2.3 billion years ago, there was enough free oxygen in the atmosphere to begin to react with iron in sediments, creating hematite and turning the resulting rocks red.

Flaming Cliffs of Mongolia, photo by Zoharby, GNU Free documentation license

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