How do plants turn into coal?

The geological process is called coalification: initially, fungi and bacteria degrade carbohydrates and other substances and convert the remains into peat. With partial to complete exclusion of oxygen, increasing amounts of water and carbon are precipitated a process during which, over the course of millions of years, coal is formed: the loose lignite, the denser hard coal and, ultimately, anthracite, which almost completely consists of carbon.

While all this was taking place under the surface of the earth, the area was alternately traversed by rivers, covered by subtropical shallow seas and by layers of ice several kilometres thick. Animals such as giant snakes, crocodiles, or the large flightless bird Diatryma (measuring up to 6.6 ft), fox-sized primordial horses, tapirs, rhinoceroses, etc. moved across the earth, until eventually, in our days, wolves, bears and elk have almost become extinct. Giant redwoods, ferns, great horsetails and many others plants emerged and disappeared in a continuous process of come and go. Time never stood still.

Here you can find out more about the individual epochs in the process of coal formation.

Moorland

65 to 35 million years ago

The ascent through the pile of strata takes us from the foot of the open-cast mine to the tropical world of the Eocene, the second of five epochs in the Tertiary Period. Oppressive heat and high humidity paralyse the movements and make sweat pour from every pore. Powerful groves of pines and laurel as well as luscious undergrowth vegetation turn the walk through the evergreen tropical forest into an adventure. The sound of flowing and dripping water is everywhere. Expanses of moor and marshland are traversed by broad, sluggish rivers overgrown with ferns and trees that may at times develop into huge torrential streams. On riverbanks and in lakes, animals appear to be living a paradisiacal life. Crocodiles, snakes, turtles, frogs and countless insects inhabit the wetlands.

The primordial ancestors of horses, tapirs, prosimians and various predators are roaming the area. Bright colours and diversity are the characteristics of tropical forests in the lowlands. Animal life is dominated by an apparent joyfulness. But also death is part of what nature holds in store, the animals are threatened in a variety of ways: they may fall victim to the food chain, they may drown during food intake at the swampy water points or during flight in the moorland, they may fall down one of the numerous landslides of the karst landscape marked by underground leaching or they may be swept away during the rainy season by a torrential river carrying uprooted trees in its stream. Dangers lurk everywhere and yet it all looks like paradise - a world carefully controlled by nature. The climate changes slowly over thousands and millions of years. Noticeable changes in the landscape associated with this climate change. The sea level is rising and almost imperceptibly, the prehistoric North Sea draws closer to the Middle German mainland. The inland tropical forest with its flora and fauna becomes a coastal landscape. The inland tropical swamps and forest moorlands have changed into coastal moorlands. Storm tides drive the water up into the estuaries of the everglades until far into the hinterland. The prehistoric North Sea slowly begins to dominate what until then was landlocked country. The time of the complete flooding of the mainland by sea is already looming on the horizon.

Sea & Coast

30 to 15 million years ago

The time of coal formation is now over. In the pile of strata, the dark coal layers end abruptly, and marine deposits become visible. The dominion of the prehistoric North Sea over Central Germany and Silesia has begun and, with it, the sedimentation of fine marine mud, silt and sand. Layers of coastal sands and shallow water sediments repeatedly alternate with fine-grained deposits from greater depths. Wave ripples are evidence of strong seabed currents, and numerous traces of soil-dwelling organisms testify to the diversity of life in the ocean mud. The pile of strata thus reflects, next to the gradual encroachment of the prehistoric North Sea in the estuaries, the differentiated coastal flooding and the wide-scale flooding of the hinterland up to the foot of the Central German and Silesian mountains. The territories are now under complete marine coverage. In the marine sediments, there are many remains of fish, sponges, turtles, but also of dugongs and whales. They are an expression of the diversity of aquatic life.

Various land mammals of the subtropics such as giant pigs, anthracotheria ("coal beasts"), rhinoceroses, greater one-horned rhinoceroses, tapirs and chevrotains roam sandy beaches surrounded by palm trees and the pine-laurel forests of the hinterland in search for food. Over the course of time, fluctuations of the sea level steadily change both the extension and the form of the coastline as well as the living conditions of its inhabitants. Trees growing on spits of land and coastal dunes are increasingly exposed to stress caused by rising water levels and flooding as well as the associated increased pest infestation. Resin from wounded trees drips onto the sea sand and hardens into amber, the "gold of the coasts". Trapped in sticky resin, the entire diversity and beauty of the small fauna living in the subtropical coastal forests is immortalized here: flies, mosquitoes, bugs, gnats, but also butterflies and spiders and even lizards have lost their struggle for life in the "sticky blood" of the trees. By and by, the sea recedes and slowly uncovers the land. Individual subsurface elevations of solid rock emerge as islands from under sea level. The surf of the waves gnaws at islands and the coast, symbolising of the ongoing struggle for supremacy between mainland and sea. Temporarily, coastal bogs and swamps dominate the scenery, but they are always under the threat of a new attack from the ocean. Due to the cooling of the climate, the ocean eventually loses its might, the mainland returns for good and the sea has returned its power to the rivers again. Central Germany and Silesia are now for a long time part of landlocked country again.

River

Except for the period of sea floods and inland ice, rivers are the only medium that has left a lasting imprint on landscapes from the beginning of coal formation onwards. Between these two periods, rivers are the major shaping force of the mainland. As the prehistoric North Sea withdrew and the lignite swamps bordering the ocean disappeared, a period of slow and steady decrease of temperature and rainfall began. The scenery changed. The evergreen tropical forests as well as the savannahs with softwood and grass disappeared.

But time and again, the long development to the cold climate is interrupted by hopeful periods of warming which result in the spread of deciduous and coniferous forests. The fauna living in river-crossed riparian forests and open country such as sabre-toothed cats, pumas, cheetahs, hippopotamuses, rhinoceroses, cave bears, lynxes and hyenas make their reappearance in the savannah landscapes returning temporarily. However, the steadily yet unremittingly advancing cold eventually prevails. Wind and rivers are the reasons for steady change of the scenery. In the largely treeless steppes and tundras, whose vegetation mainly consists of grasses and shrubs, wide surfaces in the valleys are filled with gravel carried here by the rivers. Huge layers of gravel interspersed with frost structures become visible in the pile of strata. An extensive network of branch streams with highly fluctuating flows and winter floes characterizes the barren landscape.

Inland Ice & Frost

2.5 million to 350,000 years ago

The frost arrives. In long winters it penetrates deep into the ground. The short summers cannot drive it away from there. The gradual cooling that lasts several phases results in progressive ground frost and, eventually, in the final arrival of permanent frost. The subsoil may be frozen several meters deep. Cracks, columns and walls of ice permeate the ground. Banging sounds of frost caused by sudden drops of temperature can be heard in the nights. During the days and the short summer periods, the ground surface thaws.

Old mammoths, bisons, reindeers, Saiga antelopes and cave bears roam the barren Siberian tundra that is hit by icy, dusty winds. A shell of inland ice approaches from the north—imperceptibly, unstoppably, stealthily and quietly. Its reign begins with the damming up of rivers that turn into extensive glacial lakes. In winter, the lakes are frozen several meters thick, and in summer, numerous icebergs and floes that have come loose from the ice shield drift on them. Inland ice, mighty and sublime, covers the land. In the midst of the white-grey snowstorm, a bluish-white gleam emanates from the ice shield. Silence has settled in, it is interrupted only by the sounds of streaming meltwater, the whine of the icy winds and thundering ice. The cold has reached its peak. Slowly, it is superseded by continuous warming. Together with the ice-covered landscape, the load of boulders is uncovered that was carried here from Scandinavian countries and frozen in glaciers. Also the diversity of flora and fauna awakens to new life in the scenery from which the ice slowly recedes. And with them, man enters the region for the first time.

Interglacial Period & Man

330,000 to 110,000 million years ago

Warming, ice decay and thawing, flowing and raging rivers of meltwater and waking rivers are immediate signs of the new era after the reign of ice has ended. In the pile of strata that becomes visible in open-cast mines, sediments rich in lime and organic material occur above the alternating layers of ice-age deposits. Forests develop with meandering and gently flowing rivers and numerous lakes, ponds as well as a lush fauna.

Together with them, numerous predators, among them cave lions, leopards, wolves, red foxes, cave bears, brown bears, black bears, spotted hyena, pine martens, badgers and lynxes ramble the land. It is the time when early man makes his appearance as homo erectus; curious and searching, and endowed with a strong will to survive, he encounters initial conditions ideal for his development: a warm and temperate climate, ample food supplies and abundant raw materials of soil and solid rock for his survival. As a part of nature still equal to the animal world, his survival as hunter and gatherer begins with the search for food. Chipping floors located at riverbanks seamed with eroded Nordic flint are used to manufacture flint tools. Numerous skeletal remains preserved in the sediments testify to the habit of hunting game animals. Places where forest elephants and other large mammals were slaughtered are found on the shores of so-called "sky ponds", savannah lakes and ponds that remained during the arid region. With increasing experience and the development of his spirit, man slowly begins to transform from servant into master of nature and life. The use of fire, a sedentary existence, ritual and cultural activities, the development of using raw materials, production of materials and hunting methods are important milestones of man's development from the Paleolithic and Neolithic periods to the modern homo sapiens. In this long period, environment and climate changed about every 100,000 years, from temperate forests to Arctic tundras and back. Man remained, was always present. Adaptation, moderation in keeping with natural conditions is his recipe for success.