PALAEOBOTANY study of past organic life forms

paleobotany

1. PALAEOBOTANY (STUDY OF PAST PLANT LIFE)

2. FOSSILS (Derived from latin word ‘ Fodere ’ meaning ‘to dig’ “Fossils are the remnants of some former living beings, embedded in the superficial deposits of the past geological periods.” Not only include preserved remains of plants and animals but any associated substances such as some chemical molecules constituting body parts-chemical fossils. Hard tissues are better preserved as softer tissues decay and cannot be fossilized

3. Nomenclature of Fossils Complete plant rarely preserved Only fragments are found at different times So difficult to organize into a complete plant and to assign appropriate name

4. Nomenclature of Fossils Suggestion of Sixth International Botanical Congress (1935) Each fossilized part is given a name =status of a genus Unlike living plants, generic name is given only to parts without indicating to which plant it belongs Each part represents a form genus/organ genus/artificial genus Complete plant constructed by putting together these form genera on the basis of similarity and period to which it belongs

5. Nomenclature of Fossils

6. Rules of naming form genera Suffix signifies different parts - dendron  stem e.g Lepidodendron - phyllum  leaf: Lepidophyllum - xylon  woody part of plant: Dadoxylon - spermum,-carpon,-carpus,-stomaseed Mazocarpon , Sterocarpus,Lagenostoma - thecamicrosporangia: Polytheca ; Crossotheca - strobuscone : Androstrobus ; Lepidostrobus

7. BIOLOGICAL ASPECTS OF PALAEOBOTANICAL STUDIES Study of external and internal structure and distribution of fossils Identifying evidences in support of phylogeny & evolution of plant groups Assertion of climatic and environmental conditions of geological period under study Correlation of palaeo -climates with the distribution of plants

8. GEOLOGICAL ASPECTS OF PALAEOBOTANICAL STUDIES Determination of age of rocks Geographical distribution of coal and water Supply of useful information in the exploration of fossil fuels

9. FOSSILIZATION The process of preservation of dead organisms or their parts in the form of fossils. Can be entire organism/ hard part/ mould /cast of an organism/or its parts or imprint of a leaf on a stone. Prof. Birbal Sahni is known as “Father of Indian Paleobotany ” After his name is ‘ Birbal Sahni Institute of Palaeobotany ’ situated at Trans-Gomati River bank , Lucknow

10. FOSSIL RECORD The totality of fossils, discovered and undiscovered, and their placement in fossiliferous (fossil containing) rock formations and sedimentary layers is known as fossil record. Fossils are direct evidence for the existence of pre-historic organisms.

11. FOSSILIZATION PROCESS It is essential for fossilization that whole plant/organism be buried alive or soon after death Small number of plants gets fossilized as either they decay or eaten by termites Best conditions for fossilization are found in bogs with very cold or acidic water and low oxygen supply which stops plant decay Fine sand or mud gets deposited over plant Soon it settles on sea or lake bed and gets deeply buried Through geological changes this sediment is compressed under weight of other sediments and reaches to greater depth Finally this sedimentary rock is preserved as ‘FOSSILS’ Swamps, falling volcanic ash and snow also help in fossilization Protoplasmic contents are first to disappear, then soft parenchyma cells but harder wood and sclerenchyma or cutinized tissues are well preserved

12. It takes place by replacement of molecules of original substances of plant one by one by molecules of minerals in soil solution This replacement may occur due to hydrolysis or weathering of organic substances present in plant body Fossilization can also take place due to infiltration and precipitation of minerals through cell wall After burial, plant body undergoes partial disintegration Free carbon released in this process forms carbonates by reacting with infiltered calcium, magnesium etc.

13. THEORIES OF FOSSILIZATION Mainly there are two theories how plants become fossil 1. Infiltration theory 2. Molecule by molecule replacement theory 1. Infiltration theory Infiltration theory is based on the fact that mineral matters are infiltrated and precipitated in the cell wall in the buried plant and plant parts undergoing partial disintegration resulting in the release of free carbon which reduces the sulfides present in water and leads to the formation of carbonates of Ca, Mg and Fe. Finally silica and other compounds are deposited within the cell walls through infiltration and precipitation. The process is entirely dependent upon the preservation of organic materials within the cell wall.

14. 2. Molecule by molecule replacement theory According to this theory, the original substance of the plant body is replaced molecule by molecule in solution. There are some instances where the complete replacement has taken place. These replacements are due to complete hydrolysis of any type of organic substances except the cell wall material particularly lignin and cellulose. This replacement is gradual and supposed to be completed where lignin and suberin remain. The organic substances gradually diminished due to chemical breakdown and molecule by molecule replacement by any mineral substance like pyrite, lime carbonate or silica. Considering the chemical aspects, it appears that the idea of replacement is misleading. If silicon shows any strong affinity for organic compounds, it must build up organic silicates which are not found in the petrified wood. Therefore, the role of silica in replacement process seems untenable.

15. FACTORS EFFECTING FOSSILIZATION Nature of plant (thin/delicate/hard) Rapidity by which material is prevented from decay by organisms Changes to which rocks are subjected during/after the burial of plant part Extent of mineralization Protection against high winds Low amount of available oxygen

16. GEOLOGICAL TIME SCALE Total life span of Earth from its origin about 4600 billion years Life believed to be originated about 3000-3500 million years ago on earth Table/Time chart or time scale that subdivides the Earth’s history into geological time units Measured in millions of years Subdivision of history based on time and Earth’s stratification Based on time: Eon  Eras  Periods  Epochs

17. ARCHAEOZOIC ERA (PRECAMBRIAN PERIOD) Before 4000 million years ago Origin of Earth and emergence of life Very few fossils formed because either the environment was not suitable for fossilization or organisms present had not tissues not fit for fossilization

18. PALAEOZOIC ERA -6 periods -Aquatic and land plants -First fossils of land plants -Age of seed ferns Manograptus Sporogonites Psilophyton Cooksonia , Horneophyton

19. PALAEOZOIC ERA Presence of annual rings in Callixylon indicated seasonal changes in environment

20. Psilopsida Lycopsids Sphenopsids Dense forests made by these plants

21. Mesozoic era Triassic, Jurassic, Cretaceous periods Environment was arid, not suitable for plants requiring humid climate Age of gymnosperms Triassic period: Age of cycads Origin of angiosperms but negligible number Angiosperms formed majority vegetation in cretaceous period Salicaceae Moraceae Araliaceae

22. Coenozoic era Age of Angiosperms Tertiary Period Quaternary period Miocene Pliocene

23. Mountain ranges like Himalayas in Asia and Alps in Europe formed Effect of hot winds reduced and ice age started Gradually ice shifted to poles, resulting in formation of tropical and temperate regions Seed plants migrated towards tropical regions Plants which could not migrate became extinct Annual and Biennial herbs which could tolerate low temperature constituted vegetation of temperate and polar regions

24. Prof. Birbal Sahni : Father of Indian Palaeobotany

25. DETERMINATION OF AGE OF FOSSILS Age of fossils calculated by finding age of rocks Age of rocks calculated by using radiometric dating techniques Various radioactive isotopes of uranium (236U, 238U), thorium (232U) and potassium (40K) are used These are called ‘’geological clocks’ Radioactive isotopes decay, leading to stable isotopes with release of energy Rate of decay to stable isotope is always constant Age of rock and plant can be calculated by measuring relative quantities of radioactive isotope and stable isotope CARBON DATING technique used to determine age of plants and animals, back to about 60,000 years because half-life of carbon is about 60,000 years

26. TECHNIQUES FOR STUDYING FOSSIL PLANTS Thin ground sections A small portion of the petrified material is grounded on one surface This surface is then cemented to a glass slide with canada balsam With the aid of a special saw that has flat steel disc blades with diamond dust pressed into the cutting edge, as much as possible of the specimen is cut away, leaving a moderately thin slice adhering to the slide. The section is then ground thinner and thinner on revolving lap until it becomes transparent enough to permit transmission of light Using mounting medium the section can be sealed with cover glass for being examined in a light microscope

27. Cemented to a glass slide with canada balsam Cutting with rock cutting machine Ground thin section after grinding

28. Advantage: A thin section of petrified wood can be made that preserves the cellular structure in an unchanged condition.   Disadvantages: The technique needs extensive labour and is time-consuming,   A small number of sections can be made from a given specimen, thus a lot of material is wasted.

29. 2. FILM OR Peel technique Grind the cut surface Etch the surface with hydrofluoric acid Etching with acid removes the mineral matter from the cell cavities Wash gently with running water and air dry the etched surface Flood the etched surface with acetone and before the acetone evaporates lay a thin sheet of clear transparent cellulose acetate on the surface, with care taken to avoid air bubbles. Acetone partially dissolves lower surface of the cellulose acetate film converting it to a liquid that flows in and out around the cavities., and it now envelops the cell walls projecting from the surface.

30. Acetone being volatile evaporates quickly, once again rendering the lower surface of the cellulose of the cellulose acetate into solid form. The cell walls are now partially embedded in the sheet of cellulose acetate Allow it to dry for at least eight hours. Pull away gently the hardened film from the surface of the specimen. The resulting film which is actually a thin transfer carries with it a very thin section of 0.5 to 1.0 microns of the petrified material. This type of preparation is called a “Peel”

31. Advantages:   A series of sections can be made from a single specimen.   It is less expensive and quicker to prepare.   The sections (peels) obtained are translucent, thinner and durable.  

32. 3. MACERATION TECHNIQUE This technique is most suitable for study of peat, lignite and coal. It is very useful for pollen and spore analysis. A layer of coal is picked up with a needle and put in a glass tube containing Schultz's solution i.e. nitric acid to potassium chlorate crystal are added. It is left in this mixture for some hours. This oxidizes coal to humic acid, which is then removed by with an alkali usually with ammonia solution or potassium hydroxide. It is then centrifuged or differential filtering. Spores, pollens etc. can be recovered and then embedded in transparent media like glycerin jelly.

33. Peat Analysis ( Acetolysis Technique):   Peat Analysis ( Acetolysis Technique):   Peat Analysis ( Acetolysis Technique)

34. Lignite and Coal Analysis

35. Advantages: A small portion of sediment is enough to get considerable amount of pollen and spores.   Due to the presence of resistant chemical sporopollenin in exine , pollen and spores are considerably preserved in deposits like peat/ coal/lignite, etc. The maceration process is very simple and reliable.

36. 4. Transfer Technique Used to study venation, nature of vascular elements, epidermis and stomata Plant fragment freed from associated rock Specimen is coated with two coats of paraffin wax When film dries, rock material is removed by cutting Specimen is then immersed in 25% hydrofloric acid to dissolve away rock Finally specimens are washed, dehydrated and mounted Slow process but fossil is least destroyed DISADVANTAGE: Specimen is dense and opaque

37. 5. MICROTOME METHOD Useful for fossil woods which retain much of cell wall structure intact Specimen is made soft by keeping it in hydrofluoric acid and potassium chloride Afterwards, it is treated with mixture of phenol and 95% alcohol Then embedded in paraffin and section cutting done by microtome DISADVANTAGE: Long process for de-mineralizing and embedding

38. 6. EXCAVATION METHOD Suitable for studying minute leaves and sporangiophores Specimens removed with micro-vibratory machines or with small hammer and steel needles Slow and tedious process but excellent results Calamophyton was found by this method

39. 7. ELECTRON MICROSCOPY METHOD Xylem elements of Lepidodendron were studied by this method Shows cellulose and lignin in cell wall DISADVANTAGE: Not commonly used method due to complex equipment and lengthy procedure

40. 8. X-Ray radiography Used for studying fossils which are damaged by acid treatment in peeling and microtomy process Corresponding to density, plant X-ray photographs shows differential density. X-ray computed scans are used to generate three-dimensional (3D) models of fossil remains, to explore internal structures. Technique useful for study of calcified seeds obtained from coal balls

41. 9. CHEMICAL METHODS Principle is to identify constituents of fossil plants It is used to trace presence of chlorophyll and hemoglobin in carboniferous sediments and carotenoids . C14 technique is the most important for study of fossils