How do trees turn into coal?

How coal is made

Discarded instead of rotting

Countless trees and ferns died over the course of millions of years, and new ones grew. Humus layers formed. Where the dead plants sank in the swamp, hardly any oxygen came to the plant remains.

They couldn't be broken down here by aerobic bacteria - bacteria that need oxygen to live. That is why the dead plants did not simply rot, but turned into peat. Peat is the first stage in the process of so-called coalification, the transformation of plants into coal.

Under tremendous pressure

Marshes and peat were later inundated by oceans that carried large amounts of sand and debris with them. Over the millennia, this process was repeated several times: sometimes rocks were deposited, then dead plants.

The pressure of the heavy earth increased and pressed the water out of the peat layers. In combination with higher temperatures and a complicated biochemical process, this led to the peat initially being turned into lignite. And when the coal sank deeper and deeper, and the pressure and temperature continued to increase, kilometer depth, brown coal was ultimately turned into hard coal.

Warning: dangerous gases!

The dead vegetation was hermetically sealed. During the decomposition of these plant residues, gases developed that could not escape into the atmosphere and therefore collected in the coal: Among other things, methane, carbon dioxide, carbon monoxide, some nitrogen oxides and hydrogen.

This mine gas can explode at a concentration between five and 14 percent in the air. The miners then speak of a firedamp that can be very dangerous. That is why the best precautions are taken in mining today. Gas measuring devices constantly check the air concentration.

If mine gas appears, it is extracted before work on the coal seams even begins. A pleasant side effect: the extracted gas is a valuable source of energy and can be converted into electricity and heat in thermal power stations.

Turbulent times in NRW

About 50 million years ago, in the Tertiary Age, Europe was just separating from North America. The Rhine Trench sank and connected the North Sea with the Mediterranean. Continental plates crashed into each other and unfolded the Alps.

Volcanoes spewed fire in what is now southern Germany. So turbulent times, also in the area of ‚Äč‚Äčtoday's North Rhine-Westphalia: The Rhenish-Westphalian slate mountains formed, and the layers of hard coal, which had arisen before primeval times, were lifted up by earth faults between the Rhine, Ruhr and Lippe. There the coal seams were now exposed and waiting to be discovered and mined.

Lots of coal

Even if hard coal has been mined in Germany since the Middle Ages: there is still plenty available. For the whole of Germany, the geological reserves of hard coal were estimated at around 230 billion tons in 1998.

Because of the enormous extraction depths of more than 1000 meters, domestic hard coal is now many times more expensive than imported coal, for example from Poland or South Africa. For this reason, funding in the Ruhr area was completely discontinued in 2018.