Hundreds of millions of years ago on Earth, forests appeared.
In hundreds of millions of years later, electricity, heating, industrial development... We still have to thank the ancient forest.
Ancient forests have not only improved the earth's ecosystem, but also created coal mine resources that are closely related to our lives.
So, when did forests start to form? What does coal have to do with ancient forests?
What does an ancient forest look like?
400 million years ago, vascular plants successfully landed, and a subtle change occurred on the rocky land, that is, the soil was born and the vegetation became more and more luxuriant. Finally, about 350 million years ago, in the middle and late Devonian period, forests appeared on Earth for the first time.
So, how do scientists judge the formation of forests in the Devonian era?
The forest is made up of tall trees. The plants that make up the forest must be joben plants, at least 4 m tall and at least 7.62 cm in diameter. Only such plants have the basic conditions for constituting a forest. In plant fossil burials, it is very rare for the entire plant body to be preserved as fossils intact, and the vast majority of them only preserve a part of the plant body. Therefore, the diameter of the plant's stem is usually used to determine the height of the plant body. After statistical analysis, the diameter of the stem has a certain correlation with the height. In the middle and late Devonians, on the Earth's land, some plant stem diameters have exceeded the requirements of defining trees, more than 10cm, then its height is at least 5m, some can reach 20m, or even up to 30m.
In addition, from the analysis of the morphological characteristics of plant bodies, from the trend of almost linear decline in the relative concentration of carbon dioxide in the atmosphere, early forests may appear in the earth's terrestrial ecosystems in the middle and late Devonians.
However, to identify early forests, specific geological conditions are also required: the forest plants that grow are preserved in situ so that researchers can construct the forest appearance. In situ preservation is to preserve the position of the plant when it was alive, without going through later changes. Plant fossils preserved in situ are very precious, and they can provide important information such as plant distribution and overall characteristics. The most well-preserved and widely recognized early forest, fossils of which are from the Gilboa River Quarry in New York, USA. This is the world's earliest forest in the Late Middle Devonian period (Figure 1).
Figure 1 Fossil Gilbor Devonian stump in upstate New York, U.S
What was a sight to behold in a pristine ancient forest? It was made up of ferns such as wood thieves, sheep's teeth, and stone pines that made up the original rainforest. The 30-meter-high seal wood resembles a giant umbrella with a long handle, with only 1 meter-long leaves growing at the top. The roots of the seal wood grow many small roots, drill out of the soil for photosynthesis, and when they grow to a height of 27 meters, the trunk begins to branch, and the spores at the top are released and drift with the wind. A spore is a small genetic packet. As long as the environment is humid, it can develop into a new life. The wet and rainy swamps are a haven for these spore plants.
Figure 2 Restoration of ancient forests
10 million years after the appearance of forests, the plant world entered a period of great prosperity, ushering in the Carboniferous Period, an era of coalmaking. At that time, the climate seemed to be exceptionally warm and humid, and terrestrial plants extended from the coastal zone to the interior of the continent, forming large-scale forests and swamps, providing favorable conditions for the formation of coal. Coal reserves accounted for more than half of the world's total reserves in the strata of this period, from which the name "Carboniferous" was derived. For tens of millions of years, forests have been constantly photosynthetic and contributing oxygen, and the earth has ushered in an era of the highest atmospheric oxygen content in history. The high-oxygen environment seems to have a wonderful effect on the animal kingdom, and the small invertebrates that modern people are accustomed to, such as dragonflies, spiders, etc. have become so large in that era, dragonflies can reach 70 centimeters in one wing, and spiders are as large as ten meters, think about it is very scary!
In the middle and late Carboniferous period, new taxa evolved in the plant kingdom, such as cycads, a new taxon of seed ferns (Figure 3), ornate wood, and the order Fusonium, which is related to coniferous plants. The gymnosperm is also a tall tree that becomes one of the important plants for coal making.
Fig. 3 Seed fern tongue sheep teeth
At the same time as the composition of plant species changes, the appearance of plant communities also begins to show obvious geographical differentiation. Vegetation on the Middle and Late Carboniferous to Permian Earths can be divided into four plant geographical regions: the European and American flora distributed in Europe and most of North America, the Chinese flora distributed in eastern Asia, the Angara flora distributed in northern Asia, and the Gondwana flora distributed throughout the southern hemisphere and south Asia in the northern hemisphere. Among them, China and Southeast Asia, which belong to the Chinese flora, also belonged to the Chinese flora in the early days, and later with the change of climate and the evolution of plant species, a unique flora represented by the large feathered sheep's teeth (Fig. 4) was formed. The climatic conditions of the Chinese flora are high temperature and humidity, and the vegetation type is similar to that of the current rain forest and monsoon rain forest. Representative plants in addition to large feathers sheep teeth, there are Also Chinese sheep teeth, woven sheep teeth, petals and leaves and so on.
Fig. 4 Large feathered sheep teeth
Plant remains become energy
The Industrial Revolution, based on coal energy, is a major change in human history. Coal, as a kind of fossil energy, is a solid combustible mineral transformed by complex biochemical processes after the remains of plants in ancient times were buried by geological processes. Scientists can often find plant fossils with different degrees of preservation in the top plate and bottom rock of the coal seam (Figure 5), and the surface of the coal block can often see traces of plant leaves and rhizomes, if the coal is cut into thin slices and placed under the microscope to observe, you can find very clear plant organization and structure, sometimes in the coal seam there is still something like a tree trunk, and some coal seams are also wrapped in complete insect fossils. They provide valuable evidence for our understanding of coal plants and the natural environment at that time.
Figure 5 Plant fossils are often associated with coal formation
In the long geological history, the plant kingdom has flourished several times, and there have been several important coal-forming periods such as the Carboniferous, Permian, Jurassic and Tertiary Periods, of which the Carboniferous Period is the earliest important world-wide coal-forming period in geological history.
Coal-forming plants in the Carboniferous Period were mainly lithocarp, Koda, seed ferns and true ferns. The plant features of the Early Carboniferous are similar to those of the Late Devonian, and the composition of plants in the global range is not very large, with scaled wood, quasi-scale wood, sub-scale wood, nest wood, ancient seal wood, ancient reed wood, weak wedge leaves, clematis fern, celery sheep teeth, whiskered sheep teeth, wedge leaf sheep teeth, shovel sheep teeth and triple-split sheep teeth as the main representatives. Although most of these two types of plants are now small herbaceous plants, more than 300 million years ago, the members of their family were tall trees, and the stems of wood thieves represented by reeds could grow to 20-40 cm thick and were widely distributed along rivers and lakes and swamps. The tree stone pine (Fig. 6), represented by scale wood and seal wood, can reach a height of up to 40 meters, and they are tall and majestic, distributed in pieces, and were the main force that formed coal at that time.
Fig. 6 Scale wood and seal wood
Large-scale forests appear on Earth, widely distributed in coal-forming swamps in coastal lowlands. In addition, the movement of the earth's crust in the middle and late Carboniferous periods led to the emergence of large depression basins in many areas, providing favorable geographical conditions for the large-scale generation of coal. The rate at which the earth's crust declines in an area and the amount of plant remains pile up determine the thickness of a coal seam in a coal mine. The speed of the earth's crust falling is fast, and the plant remains are thick, and the coal seam of this coal mine is thick; conversely, the speed of the decline of the earth's crust is slow, and the plant remains are thin, and the coal seam of this coal mine is thin. And because the tectonic movement of the earth's crust has caused the original horizontal coal seam to fold and break, some coal seams are buried deeper underground, and some are squeezed to the surface, or even exposed to the ground, which is easier to be found. There are also some coal seams that are relatively thin and not large, so they have no mining value.
Early forests in China
Does our country have the conditions and possibility to form early forests? In South China, Xinjiang and other places, in the Late Devonian, there were common plants that formed early forests, such as large arborvitae pine plants, pre-gymnosperms thick stem fossils, similar to the diameter of the stem of twigs and ferns can reach 80 cm, it is speculated that the height of this plant is more than 10 m, that is, China has the plant body needed to constitute the forest.
In 2012, Chinese and American scientists discovered an in situ buried fossil forest, or coal swamp forest, about 300 million years old, in the Wuda coalfield in Inner Mongolia, which was buried by volcanic eruptions. Its preservation method is quite similar to Pompeii, and it can be said that it is a "plant Pompeii" in the biological world of the earth. Vegetation consists of six major plant groups: stone pines, arthropods, ladybirds, ferns, primitive pines, and cycads. The middle vegetation is tree ferns, which form the main body of the forest, and the upper vegetation consists of primitive conifers, or stone pine plant seals; the underlying vegetation includes knotted wedges and star leaves. This is by far the largest area of vegetation actual restoration of a land landscape from the geological period in the world.
In the Carboniferous Period, the main land masses that make up the present Chinese mainland, the North China Plate and the South China Plate, were in the middle and low latitudes, and in warm and humid climates, flourishing forests formed large coal seams in coastal and inland basin swamps. Therefore, the Carboniferous period is also the first important coal-forming period in China's geological history. For example, in Shanxi, which is known as the sea of coal, most of its coal seams were formed during this period, when the land of Shanxi underwent several sea and land alternations, and when the sea receded, the plants on the land quickly flourished in a warm and humid environment, and a large amount of coal was formed.
epilogue
Forest formation is a revolutionary event in the Earth's terrestrial ecosystem, which has greatly improved the Earth's ecosystem. Since the advent of forests, the natural environment of the continent has been renewed, which not only enriches the atmosphere with oxygen ions, creates an ecology suitable for the development of animals and plants, but also affects the global atmospheric and marine environment, and has also had a profound impact on the evolution of the global climate.
Not only that, it is these ancient forests hundreds of millions of years ago that have preserved an extremely precious energy wealth for the development of our modern industry.