When it comes to fossils, most people will first think of the huge and spectacular skeleton fossils of dinosaurs, and if you mention the various plants that have survived in the long history of the earth, most people will probably only think that coal is formed by ancient plants.
It is true that coal is formed by the complex changes of plant debris, but the remains of ancient plants are not just coal. Plants have also formed a huge number of fossils, although not as shocking as the skeleton fossils of large animals, but plant fossils, like animal fossils, can bring us a lot of information from ancient times. From these "fragments", we may never be able to piece together a complete picture of history that has disappeared, but it is enough to give us a glimpse of its beginnings, to satisfy our curiosity to a certain extent, and to give us inspiration about the present and the future.
Human research on the origin of fossils can be traced back to the 6th century BC. At that time, ancient Greek scientists had correctly explained the fossils, pointing out that the fossils were the remains of organisms that lived in ancient times when the natural conditions were very different from those of the time. By the 4th century BC, Aristotle proposed that fossils were naturally generated, formed by the evaporation of gases deep underground—a hypothesis that influenced the entire Middle Ages and even later.
By the time of the Renaissance, there were all sorts of odd theories about the origin of fossils: some people said that fossils came from tiny stone seeds that grew underground and died underground; some people thought that fossils were "the failure of the Creator" and therefore had no life; others said that fossils were made by Satan in order to compete with God, and they failed.
In the 16th century, the great genius Leonardo da Vinci also became interested in fossils, he rejected Aristotle's theory of natural generation, and gave a correct explanation of the formation of fossils, but unfortunately no one sorted out his manuscript until the 19th century.
Obviously, not all living remains have survived, and only a very small number of organisms have been fossilized under certain conditions – there are about 1.7 million species of organisms that have been recorded and named on Earth today, and only more than 200,000 species that have been discovered so far and have lived in a long geological history of billions of years; from this extreme disproportionateness, our understanding of the past inhabitants of the earth is quite limited.
In addition to directly telling us about the various paleontology in the history of the earth, fossils can also help us understand the geology, climate and major natural events of ancient times. For example, the petrochemical wood mentioned earlier can tell us the meteorological data of ancient times: the temperate zone has four distinct seasons, so the annual rings are very clear; while the tropical seasonal changes are very small, the cells formed are not different, and the annual rings are not so distinct. A meticulous study of some leaf fossils has the potential to extrapolate the amount of carbon dioxide on Earth hundreds of millions of years ago.
The historical information retained in fossils lies not only in the fossils themselves, but also in the organic combination of fossils and geological phenomena of origin – only by analyzing them together with the geological environment in which they are located can scientists obtain more and more accurate information about sunlight, rain abundance, thousands of years of climate change, plant community combinations and so on.
However, the situation of fossil resources being stolen and destroyed around the world is shocking. For example, in Arizona's Fossil Forest National Park, under strict protection, more than 12 tons of fossils are smuggled away by tourists every year, equivalent to nearly 10,000 pieces; the Cycad Fossil National Park, established in 1922 in Southern Kodatha, was revoked in 1957 due to the damage.
Specific to ancient plants, from the fossil information, we can see how plants step by step from the ocean to land, how to adapt to each other with animals, co-evolution, how to adapt to natural factors such as climate change, and gradually eliminate species that cannot adapt. Comparing the differences between ancient plants and modern species, we can see in what direction plants are evolving.
Those plants that have disappeared in the distant past and exist only in fossils can only be restored by the fragmented information in fossils, and their existence and everything about them mainly comes from the information that paleobotanists read from fossils, and the specific reasons for their disappearance may always be a mystery.
It is not uncommon for entire animals (or their entire skeletons) to form fossils, and we can generally see many fossilized animal skeletons with teeth and claws in paleontological museums (which is also an important reason why people's impression of ancient animals is far more profound than that of ancient plants).
But in the plant kingdom, the situation is different, and the chances of the entire plant body being preserved as fossils are minimal; the fossils of various plant fragments are generally seen, most commonly leaves.
The most common type of plant fossil is the imprinted fossil. The covered sediment presses downward on the plant fragment due to gravity, forming an imprinted fossil. Imprinted fossils can be divided into two types: plants are flattened into a thin carbon film under this compaction, and if this film is preserved, this fossil is called a pressed fossil; if it is not preserved, it forms an imprint fossil. The imprinted fossil preserves the shape and surface details of the plant fragments.
If the sediment around the plant fragment hardens before the powerful compaction occurs, it is possible to preserve the three-dimensional information of the fragment.
In the hot springs we can see such a process. The leaves, stems, etc. that fall into the spring water are wrapped in calcium carbonate in the water before decay, forming a clear "mold" (imprint); later, the plant body itself decays and decomposes, but leaves a cavity in the deposition of calcium carbonate; later, the cavity is filled with other sediments, and it forms a "cast" that is exactly the same as the plant body. This form of preservation that forms imprints and castings can be done not only by depositing calcium carbonate, but also by other enriched minerals such as rhodite. Such fossils are thought to have been formed by the mineralization of plants themselves.
The central cavity of the stem of a plant can form another type of cast fossil. The stem falls into the water, and before the surrounding tissue decays, its central cavity is filled with sediment, and after the surrounding tissue decays, it retains the casting of the internal sediment, which is called the "nucleus pulp". For example, the hollow stem of the reed is very easy to form this fossil.
In addition to the general petrified wood, there are two kinds of relatively rare: protein petrochemical wood, mainly opal minerals; agate petrified wood, mainly agate minerals.
When the infiltrative filler in the petrified wood is a crystalline dense and delicate chalcedony, it is later impregnated with an iron-containing mineral solution, which will show a charming red color, similar to agate. This petrified wood has a jade-like texture and color, and it is difficult to associate it with plants if it is not possible to identify the structure of the rings and cells in some places.