On a recent hike along an ancient riverbed, I came across a slab of wood partially blocking the path.
It was only as I lifted the chunk that I realized something wasn’t right – the wood seemed far too heavy, and shimmered in the light as I took a closer look. This was no normal piece of wood. Well, not anymore.
The stone I held in my hand was petrified wood, the rockified remains of a tree that lived perhaps a hundred million years ago. Petrified wood is rare but present in and around the Appalachian mountains, and was formed in global processes somewhat similar to those that also made the vast coal deposits we still rely on for about a quarter of our electrical power.
Strangely enough, most large global coal deposits all seem to have been made around the same time, during a time known as the Carboniferous period around 300 million years ago.
Most of the terrestrial world of 300 million years ago was densely covered in lush forests, populated by huge animals and mammoth plants. Trees during this time were still fine-tuning their structures and filled their woody interiors with lignin, an incredibly resilient material that is also highly resistant to decay.
Only a few organisms are known to be able to break down lignin, with most of them being microscopic fungi and bacteria. Scientists have long believed that piles of woody material built up on forest floors during this time due to the fact that microscopic decomposers were still developing the ability to feed on lignin.
Some dead wood during this period found its way buried underneath water and/or wet sediment, further sheltering it from the effects of wood eating microbes. Held in such a suspended state, the wood broke down incredibly slowly as it was subjected to water percolating throughout its whole.
If the water was sediment-rich, silica and calcite built up around cells and other structures. Slowly over thousands of years, eventually the piece turned entirely to stone, formed into the shape of a plant that had long since eroded away.
Petrified wood takes on a variety of colors depending on the minerals present in the area it was created.
Coal is believed to be made in a similar manner, wherein peat and other organic materials are submerged in water or wet environments that help stave off microbes.
The plant material eventually makes its way deep underground, becoming subjected to the intense pressure and heat needed to create coal. In popular scientific thought, a main factor bridging these two processes was the fact that ancient microbes responsible for proper plant decomposition were slow and inefficient, giving dead wood and plant material additional time to become petrified or crushed into coal. This belief might soon be tossed by the wayside, however, as recent studies have sought to dispute its core tenants.
Although most of the fungi and other plant decomposers around today are believed to have evolved towards the end of the Carboniferous period, some scientists think there were almost certainly other organisms before them that specialized in breaking down lignin and other plant products.
Rather than attribute global buildups of coal during that time to a fault in microbes, they instead point to tectonic and other large scale processes that were taking place.
In fact, the massive landmass known as Pangea was in the process of being formed during the Carboniferous, and multiple continents were crammed together in a relatively short timespan. This rapid influx of continental collisions led to large swaths of organic material being quickly transported far underground.
According to new research, perhaps it was this Pangeal party that led to most of the global coal deposits being created around the same time.
Brannen Basham is a writer and horticulturalist. Together with his wife, Jill Jacobs, he owns Spriggly’s Beescaping. He published his first book, “A Guide to the Wonderful World Around Us: Notes on Nature.” For more information visit www.sprigglys.com.