Biodiversity: Prehistoric Periods of Earth

Prehistoric period divided into: era, period and epoch. The record is given on the basis of:

  • Data derived on the basis of character of the earth’s strata and the fossils that they contain.
  • Fossils of some pteridophytes & gymnosperms.
  • Distribution of gymnosperm plants in prehistoric times.
  • Overall distribution of plant life: pre-historic to modern days.

Paleontological Record

Psychozoic era: Dominance of man and herbaceous plants

Recent or postglacial time

20,000 yr.

Receding of polar ice caps, moderate rise of temperature, temperature zonation, aridity of intermontane regions.

Wane of forest trees, dominance of herbaceous plants, and of civilized man.

Cenozoic era: Dominance of mammals and angiosperms.

Late Cenozoic

(Neogenic period)

25,000,000 yrs.

Pleistocene or glacial epoch Ice caps and glacial conditions extending from poles into temperate zones. Extinction of many large mammals and trees. Survival of hardy adaptable types, especially herbaceous plants. Elevation and extension of continents. Beginning of civilization.
Pliocene epoch Moderate cooling of climate with increasing aridity. More restrictions of forests. Appearance of man. Elevation of the Andes.
Miocene epoch Slight cooling of climate with aridity in places. Decrease of forest areas. Increase of grasses and culmination of mammals. Elevation of the Swiss Alps.

Early Cenozoic

(Pleogenic period)

60,000,000 yrs.

Oligocene epoch Warm, moist climate. Zenith of forest areas.
Eocene epoch Climate cool and semiarid, then warm and humid. Extension of forests into polar regions. Wane of archaic mammals. Appearance of marine mammals and of primates. Continued elevation of the Rockies.
Mesozoic era: Dominance of reptiles and gymnosperms.

Upper Cretaceous period

100,000,000 yrs.

Fluctuating climate. Increase in modern forests, including birch, walnut, and maple. Extinction of dinosaurs. Increase of mammals. Appearance of marine mammals and of primate. Continued elevation of the Rockies.

Lower Cretaceous period

120,000,000 yrs.

Tropical climate, depression of land with invasion of seas continuing into upper Cretaceous. Earliest known palms and grasses. Beginnings of modern forests including poplars and sassafras. Zenith of dinosaurs.

Jurassic period

145,000,000 yrs.

Gradually rising temperature; colder at poles. Widespread warm seas. Increase of dicotyledons. Appearance of numerous toothed birds and flying reptiles. Dinosaurs predominant. Beginning of the Sierra Nevadas.

Triassic period

170,000,000 yr.

Warm, semiarid climate. Shallow warm seas and lagoons. Gymnosperms pteridophytes continuing to wane but still dominant. Probable origin of dicotyledons. Rise of dinosaurs. Appearance of mammals. Extended lands.
Paleozoic era:

Dominance of fishes and Pteridophytes

Permian period

210,000,000 yrs.

Dry, glacial climate especially in Southern Hemisphere. Appearance of the Glossopteris-Gangamopteris flora. Gymnosperms beginning to wane but still dominant. Great mortality of specialized animals and plants. Land vertebrates increasing. Extensive salt deposits.

Pennsylvanian period(upper Carboniferous period)

255,000,000 yrs.

Climate warm and humid. Pteridophytes reach zenith and begin to wane; gymnosperms reaching zenith. Increase of reptiles and insects. Amphibians abundant. Extensive coal deposits from pteridophytes and gymnosperms.

Mississippian period(Lower Carboniferous period)

285,000,000 yrs.

Land climate temperate, seas cool. Winter climate in mountains. Gymnosperms approaching zenith. Sharks and crinoids abundant. Amphibians increasing. Thin coal deposits.

Devonian period

325,000,000 yrs.

Warm climate with moderately dry air. Rapid increase of pteridophytes and gymnosperms. Appearance of amphibians. Fishes predominant. Earliest fossil record of land plants.

Silurian period

350,000,000 yrs.

Warm climate, semiarid in certain regions. Probable increase of pteridophytes and gymnosperms. Appearance of scorpions, myriapods,  and lungfishes (first air-breathing animals)

Ordovician period

410,000,000 yrs.

Continued warm climate. Possible origin of gymnosperms and increase of pteridophytes, but marine algae still dominating. Corals, bryozoans, cephalopods, and brachiopods abundant. Appearance of armored fishes.

Cambrian period

500,000,000 yrs.

Warm, uniform climate over the earth. possible origin of pteridophytes. Marine algae dominating. First known marine animals (trilobites and brachiopods)





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About Mst. Nusrat Jahan Nitu

Mst. Nusrat Jahan Nitu
A 1st-year student of Department of Botany at the University of Dhaka. Opportunity seeker. Hope to do something remarkable.

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