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September 10, 2016 Weekly Geology Guess. Pennsylvania Period

September 10, 2016

Greetings from the Bluff Park Back Porch, way up yonder on Shades Mountain (1,109′) in Alabama:

My discussion on Alabama Geology will continue with the Geologic Time Scale or the Geologic Column and the critters that abide within each pigeon holes.

As with most sciences, especially natural sciences, we love to pigeon hole our data.  Most of the pigeon holes have scientific merit and accuracy.  With the Geologic Time Scale we start with the oldest layers and work upward to the youngest layers.

For some of you this will be new, novel, and maybe heretical.

Expedition Earth: Geological time scale
Pennsylvanian Period

“The Pennsylvanian (also known as Upper Carboniferous or Late Carboniferous) lasted from roughly 323.2 million years ago to 298.9 million years ago Ma (million years ago)”

Note:  As a geologist we usually do not talk in number of years but in periods, epochs, and eras.

“The Coal Age

Carboniferous coal was produced by bark-bearing trees that grew in vast lowland swamp forests. Vegetation included giant club mosses, tree ferns, great horsetails, and towering trees with strap-shaped leaves. Over millions of years, the organic deposits of this plant debris formed the world’s first extensive coal deposits—coal that humans are still burning today.

The growth of these forests removed huge amounts of carbon dioxide from the atmosphere, leading to a surplus of oxygen. Atmospheric oxygen levels peaked around 35 percent, compared with 21 percent today. It also may explain the giant creepy-crawlies that now emerged—the size reached by insects and similar creatures is thought to be limited by the amount of air they are able to breathe.

Deadly poisonous centipedes some six feet (two meters) in length crawled in the company of mammoth cockroaches and scorpions as much as three feet (one meter) long. Most impressive of all were dragonflies that grew to the size of seagulls. One exquisitely detailed fossil of a dragonfly that died 320 million years ago shows it had a wingspan of 2.5 feet (0.75 meters).

How insects first became airborne remains a mystery. Theories suggest their wings may have developed from structures used to regulate temperature (such as by catching the sun’s rays to heat up), or perhaps they evolved from brightly colored signals used to attract mates and ward off rivals. Another idea is that insect wings developed from appendages used to glide between trees in the Carboniferous forests.

Amphibian Evolution

Amphibians were also growing in size and diversity. There were predatory species that resembled modern-day crocodiles. Armed with vicious teeth, they reached lengths of almost 20 feet (6 meters). Some amphibians developed a thicker, scaly skin, solving the problem of them drying out if away from water too long. They also reduced their reliance on wetland habitats through a crucial evolutionary adaptation known as the amniote egg. This protected the embryo inside with a fluid-retaining membrane while still allowing in air. In time, the earliest reptiles appeared. Identified from remains found inside fossilized Carboniferous tree stumps, they were small, agile, lizard-like animals.

Africa collided with eastern North America in the late Pennsylvanian, an event that formed the Appalachian Mountains. Vast coal swamps stretched across the lowlands to the west of the rising mountains.

By the end of the Carboniferous, the Earth’s landmasses were moving toward a single, global supercontinent called Pangaea.”

Pennsylvanian Period Images;_ylt=A0LEVjS_XdNXn3AAFXMPxQt.;_ylu=X3oDMTByMjB0aG5zBGNvbG8DYmYxBHBvcwMxBHZ0aWQDBHNlYwNzYw–?p=Pennsylvanian+Period&fr=yhs-befrugal-002&hspart=befrugal&hsimp=yhs-002

The Alabamian Pennsylvanian Period shows up in our state as the bituminous coal fields of Central and North Alabama.  These include the Warrior, Cahaba, Coosa, and Plateau Coal Fields.

>    As some of you will notice, as we go up the geologic column the more complex and numerous life becomes.

As with most of my weekly fores into geology, with each topic I could write many papers and dissertations.

Note:  I have intentionally reduced the amount of linked graphics in this email due to the amount of space required and trying to untangle everything the following week has been a mess.


References include:

–    Wikipedia



Editors Note:  It is the intent of this site to keep this discussion as simple as possible, so as to educate the interested general public and not to discuss with the geology crowd the latest geologic theories and nuances.  Thanks, R


“No copyright infringement intended.
The rights belong to their respective owners”
Copyright Disclaimer: Under Section 107 of the Copyright Act 1976, allowance is made for “fair use” for purposes such as criticism, comment, news reporting, teaching, scholarship, and research. Fair use is a use permitted by copyright statute that might otherwise be infringing. Non-profit, educational or personal use tips the balance in favor of fair use.


Author’s Request:  If you see any pictures that you know the source and photographer, let me know immediately.  Thanks!  R

Images have been searched by TinEye Reverse Image Search.


Next time we will venture into the Permian Period.


Enjoy the adventure!






Pennsylvanian Age Swamp



















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