Coal and Climate – Past and Future

Coal Seam

Coal is found all over the world

Predominantly in places where prehistoric forests and marshes existed before being buried and compressed over millions of years.

Prehistoric Forests?

Wow … So, coal was once plants: trees, bushes, ferns, flowers, and peat.  That’s amazing! 

Coalification

There are four major types (or “ranks”) of coal. Rank refers to steps in a slow, natural process called “coalification,” during which buried plant matter changes into an ever denser, drier, more carbon-rich, and harder material. The four ranks are:

Anthracite: The highest rank of coal. It is a hard, brittle, and black lustrous coal, often referred to as hard coal, containing a high percentage of fixed carbon and a low percentage of volatile matter.

Bituminous: Bituminous coal is middle-rank coal between sub-bituminous and anthracite. Bituminous coal usually has a high heating (Btu) value and is used in electricity generation and steel making in the United States. Bituminous coal is blocky and appears shiny and smooth when you first see it but look closer and you might see it has thin, alternating, shiny, and dull layers.

Subbituminous: Subbituminous coal is black in color and is mainly dull (not shiny). Subbituminous coal has low-to-moderate heating values and is mainly used in electricity generation.

Lignite: Lignite coal, aka brown coal, is the lowest grade coal with the least concentration of carbon. Lignite has a low heating value and a high moisture content and is mainly used in electricity generation.

The precursor to coal is peat.

Peat is a soft, organic material consisting of partly decayed plant and mineral matter. When peat is placed under high pressure and heat, it undergoes physical and chemical changes (coalification) to become coal.

Powder River Basin

The biggest coal deposit by volume is the Powder River Basin in Wyoming and Montana, which the USGS estimated to have 1.07 trillion short tons of in-place coal.

Of the factors involved in coalification, temperature is much more important than either pressure or time of burial. Subbituminous coal can form at temperatures as low as 95 to 176 °F while anthracite requires a temperature of at least 356 to 473 °F.

Although coal is known from most geologic periods, 90% of all coal beds were deposited in the Carboniferous and Permian periods, which represent just 2% of the Earth’s geologic history. Paradoxically, this was during the Late Paleozoic icehouse, a time of global glaciation. However, the drop in global sea level accompanying the glaciation exposed continental shelves that had previously been submerged, and to these were added wide river deltas produced by increased erosion due to the drop in base level. These widespread areas of wetlands provided ideal conditions for coal formation. 

Wildfires

Favorable geography alone does not explain the extensive Carboniferous coal beds. Other factors contributing to rapid coal deposition were high oxygen levels, above 30%, that promoted intense wildfires.

Current Global Warming

“Climate change” and “global warming” are often used interchangeably but have distinct meanings. Similarly, the terms “weather” and “climate” are sometimes confused, though they refer to events with broadly different spatial- and timescales.

Has the Earth been hotter than it is now?

Earth’s global surface temperature has increased by around 1.1 °C compared with the average from 1850–1900—a level that hasn’t been witnessed since before the last ice age, some 125,000 years ago.

125,000 Years Ago?

But Wait … at the beginning of this article it is stated that coal is predominantly in places where prehistoric forests and marshes existed before being buried and compressed over millions of years.

What’s so fascinating about Coal?

What this article is really about is my fascination with Coal.  I love collecting rocks, minerals & gems. 

This is my 10 pound chunk of coal.  To me it is beautiful.

It is part of Earth’s past.  It also makes me think about our future and the cycle the Earth goes through. 

Will someday our beautiful forests, like the Sequoia’s, be coal?

The cycle of our Earth will be in a future post.