This article provides an essay on palaeobotany.
Introduction to Palaeobotany:
Palaeobotany or Paleobotany (American spelling) is a study of the plant life of the geological past. It is a branch of the wider geological science of Palaeontology (Paleontology) which deals with both animal and plant remains. In Palaeontology animal remains get predominance over plant remains as the former are more numerous.
The Earth cooled down from a hot mass and there have been gradual as well as catastrophic changes before the Earth came to its present condition. The first surface of land masses was formed by the igneous rocks. It was mostly covered by water and first life arose in this water.
Then the Earth took its shape, the land masses became conspicuous and life migrated from water to land. The original rocks gradually got worn out and probably does not exist anywhere on the land surface today. The torrential rain of those days brought down the debris of the worn-out rocks to the seas, lagoons and river mouths of those days.
The debris settled down and consolidated to form sedimentary rocks. The sedimentary rocks that have accumulated so far could have been as much as 70 miles deep. But since the face of the Earth changed from time to time, there is perhaps no place where uniform sedimentation went on for all these years.
The nature of sedimentation also changed from time to time with changes in the constitution of the sediments, in the topography of the area, in the water-flow etc. This caused stratification of the sedimentary rocks.
The sequel of the strata may be irregular due to similar reasons. At a place water might have receded and come back again so that a number of strata may be missing or some strata might have got eroded by a river valley. Finally, catastrophes like earthquakes, landslides, etc., may cause such an upheaval that an upper strata may go down below an older one or the whole sequence may be reversed (Fig. 503).
It is possible to ascertain the ages of the rocks, sedimentary or igneous, by scientific methods. Study of radio-isotopes has enabled more or less correct estimation of the ages of rocks. For rocks not more than 50000 years old it is possible to make accurate estimates of their ages by studying the radiocarbon (C14) in their organic constituents. The age of the Earth thus estimated has been divided as shown in Table I.
With the advancement of age, Life evolved and the main evolutionary changes are also noted on the Table. The time scale, in millions of years, is according to what is accepted by the United States Geological Survey. But it should be clarified that the time scale given for the different periods is only approximate.
Thus, the total age up to the lowest Precambrian rocks, which has been assumed to be 3000 million years here, has been extended to 4500 million or even 5000 million years by others.
There are local names for tire different strata in different parts of the world and some Indian names (Gondwana Group) are cited later.
The plant remains that are found in these rocks are known as fossils. The word fossil came from the latin verb fodere which means ‘to dig’. Thus, in the original sense, it means anything dug out. But now the word is exclusively used in connection with organic (plant or animal) remains.
In its correct sense fossils include not only the remains of organisms or of parts of it but also anything connected with an organism proving its existence.
Thus, a chemical which could not exist without an organism or a prehistoric trail mark of a worm on a stone is also a fossil. The actual nature of fossilisation depends on the environmental condition in which it takes place. Dead plant remains are liable to get disintegrated and it is only rarely that they get fossilised.
Naturally, the softer parts disintegrate early so that chances of fossilisation are better for harder parts and specially for those with stiff skeletons.
It cannot be expected that a large plant or a tree would get fossilised in its entirety.
Usually, fossils of only bits of plants are found and those bits are then placed in some form genus without actually indicating to what plant it belongs. Stigmaria (rhizophores of Lepidodendrids), Lepidostrobus (strobili of Lepidodendrids), etc., are such form genera. In naming such form genera usually suffixes, signifying which part of the plant it came from, are applied.
Thus -phyllum means a leaf; -pteris is a fern-like stem or frond; -dendron is a tree trunk; -xylon is a woody part; -spermum, -carport, -carpus, -stoma are seeds; -theca is microsporangium while -strobilus or -strobus signifies a cone. In such cases it is the work of the palaeobotanist to collect bits of such fossils, (i.e., form genera) and to reconstruct the whole plant as it existed.
Such work is certainly very difficult and sometimes may even lead to errors.
Palaeopalynology of Palaeobotany:
Palynology is the science of studying pollens of plants. A branch of this is Palaeopalynology which is the study of fossil pollens only. Theses pollens are found abundantly in peats. They are also found in alluvial soil and even in strata below. They are found in stratified layers, so that their age may be calculated.
Study of them is useful in tracing the history of plant communities, showing the climate at the time they were shed, studying its influence on the environment and a future find of the same combination of fossil pollens is used in dating of the deposits.
A very important use of palaeopalynology in modern days is that the presence of oil bearing strata is indicated by certain deposits. During boring for oil pits it has been useful to examine the fossil pollens in every depth which may serve as a surer indication of the presence of oil or even other minerals.