(i) Became more numerous.
(ii) Progressed from simple to more complex forms.
(iii) Many transitional forms have been discovered that link old fossils to modern species, e.g., fossils of various pre-human and
human types which show the changes in shape and size of skull during the evolution of man.
(iv) Certain life forms are restricted to certain geological time span.
- Differences between the past and present forms of life: Fossil studies showed that plants and animals that existed
in past were different from their related living forms. This proves that living organisms are mutable.
Table : Geological time scale with notes on events in the evolution of life and environment
Epoch Geological and climatic
conditions
Flora (Plant life) Fauna (Animal life)
Recent
(Holocene)
End of last ice age, climate
warmer, climatic zones
distinct.
Dominance of herbs. Age of man, development of human
culture and society.
Pleistocene Periodic continental glaciers
in north.
Increase of herbs, great
decrease of woody plants.
Age of man, extinction of many large
mammals.
Pliocene Cool and temperate
climate away from equator,
continuous rise of mountains
of Western North America.
Decline of forests, spread of
herbs and grassland.
Abundant mammals, man evolving,
elephant, horses and camels almost
like modern models.
Miocene Cooling of climate. Development of grasses,
reduction of forests.
Mammals at height of evolution, first
man like apes.
Oligocene Lands lower, climate warmer. Worldwide tropical forests,
rise of monocots and
flowering plants.
Archaic mammals extinct, appearance
of modern mammals like monkeys
and apes.
Eocene Zoned climatic belts well
established.
Extension and dominance of
angiosperms.
Placental mammals diversified and
specialised, hoofed mammals,
e.g., horse and carnivores established.
Paleocene Development of climatic
belts.
Modernisation of
angiosperms.
Evolutionary explosion of mammals
and origin of primates.
Rocky Mountain Revolution (Little destruction of fossils)
Birth of modern reptiles,
development of climatic
diversity.
Rise of flowering plants
especially monocotyledons,
decrease of gymnosperms.
Dinosaurs reached peak, became
extinct, toothed birds became
extinct, beginning of teleost fishes
and modern birds, archaic mammals
common.
Culmination of worldwide
warm climates.
Cycads and conifers
common, appearance of first
known flowering plants.
Dominance of dinosaurs, appearance
of first toothed birds, spread of reptiles,
rise of insectivorous marsupials.
Continents exposed, world-
wide subtropical climate.
Gymnosperms dominant,
declining towards end,
extinction of seed fern.
Transition of reptiles to mammals, rise
of progressive reptiles and egg laying
mammals, extinction of primitive
amphibians.
Coenozoic (Age of mammals and angiosperms)
Period
Era
Quarternary
Tertiary
Mesozoic (Age of reptiles)
Cretaceous
Jurassic
Triassic
