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!

Monday, June 2, 2014

June 2. Mississippian time

The time span of the Mississippian is about 36 million years. It began with the end of the Devonian about 359 million years ago and it ended about 323 million years ago. As with all the subdivisions of geologic time, there are error bars on these dates, in this case about a half million years, plus or minus, on both ends.  

Mississippian time (from Wikipedia)
In Europe, the Early Carboniferous, the equivalent in time to the Mississippian, is divided into three ages which correspond to three stages in the rock record. The Tournaisian and Viséan are named for rocks in Belgium and the Serpukhovian is from outcrops in Russia. They span from 7 to 17 million years each.

In North America, there are four subdivisions of Mississippian time. From oldest to youngest they are Kinderhookian, Osagean, Meramecian, and Chesterian. These names are used a lot in the literature on Mississippian rocks, and I may use them too – but I will try to avoid too much jargon and I’ll try to always refer any names like that to the part of the period we’re in, and about how many million years ago it was.

As I’ve said before, international agreements are often needed to assign specifics to the breaks in geologic time. Since rocks in one part of the world don’t necessarily record the same events as other parts – or the same event may span some time and may occur at one time here, and another there – because of that, it’s not surprising that we really cannot make an exact, world-wide time scale that applies everywhere. But things do usually work out so that they’re pretty close.
—Richard I. Gibson

No comments:

Post a Comment