History of Life on Earth
  1. Precambrian Time
  1. Hadean Eon (Azoic)

    2. 1. 4.5--3.9 billion years ago Earth forms as a solid planet—no evidence of life

  2. Archean Eon

1. 3.9—2.5 billion years ago Earth’s permanent crust, oceans, and atmosphere are

Formed
  1. Earliest life forms evolve in the seas—prokaryotes (single-celled with no

(Nucleus) and cyan bacteria (blue-green algae)
  1. Proterozoic Eon
  1. 2.5 billion—540 million years ago Plate tectonics slows to same rate as present,

    2. Large mountain ranges form, and oxygen levels increase as Earth develops ability

    To obtain energy through photosynthesis

  2. Eukaryotes evolve (single-celled organisms with a nucleus)
  3. Multi-celled, soft-bodied marine organisms (metazoans) evolve
  1. Paleozoic Era (Ancient Life)
  1. Cambrian Period
  1. 540-490 million years ago sedimentary rocks form in shallow seas
  2. Multiple collisions of Earth’s plates give rise to a super continent with a mild climate
  3. Marine metazoans with mineralized skeletons (sponges, bryozoans, corals,

    4. Brachiopods, mollusks, arthropods, and echinoderms) flourish

  4. Plant life limited to marine algae
  1. Ordovician Period
  1. 490-443 million years ago North America, Europe, and Africa emerge
  2. Corals, crinoids, and clams evolve as well as the first early vertebrates—

    3. Primitive fish with bony armor plates

  3. Mass extinctions of marine life occur, allowing benthic (bottom-dwelling)

And plank tonic (floating, swimming) organisms to evolve
  1. Silurian Period
  1. 443—417 million years ago withdrawal of ocean beds leaves "red beds"
  2. Rapid evolution of suspension feeders and pelagic (open ocean) predators
  3. Fish develop jaws and the first sharks appear
  4. Earliest land plants appear as leafless, vascular psilophytes
  1. Devonian Period
  1. 417—354 million years ago Europe and North America merge with a warm,

    2. Moist climate

  2. Called the Age of Fish this period is dominated by various forms of fish
  3. The ozone layer forms and the first air-breathing arthropods (spiders and mites) move to land
  4. Amphibians evolve
  5. Plant life, including lowland forests develop and spread over the planet
  1. Carboniferous Period
  1. 345—290 million years ago two major land masses form and the climate

    2. Changes to cool and dry with a long interval of glaciations

  2. Fish continue to diversify but armored fish become extinct
  3. Insects flourish and the first reptiles evolve
  4. Land environments are dominated by plants from small shrubs to tall trees
  1. Permian Period
  1. 290—248 million years ago a single super continent forms with glaciations in

    2. Some areas and hot, dry deserts elsewhere

  2. Mass extinctions occur among corals, bryozoans, and other invertebrates
  3. Insects evolve into modern forms; dragonflies and beetles appear
  4. Amphibians decline in number and reptiles undergo evolutionary development

Of various forms

III. Mesozoic Era (Middle Life)

  1. Triassic Period
  1. 248—206 million years ago the general climate is warm becoming semiarid

    2. To arid

  2. Early dinosaurs form (very small compared to later forms)
  3. Marine reptiles evolve
  4. Ferns, cycads, ginkgoes, and conifers flourish
  5. Mass extinctions occur reducing some marine and terrestrial groups by up to

75%
  1. Jurassic Period
  1. 206—144 million years ago the Atlantic ocean begins to form
  2. Dinosaurs are dominant on land
  3. The first bird appears
  4. Frogs, toads, and salamanders appear
  1. Cretaceous Period
  1. 144—65 million years ago the continents are shaped much like they are today
  2. The global climate is warm and the poles are free of ice
  3. Dinosaurs peak as the dominant vertebrate life form and extend throughout

    4. Every continent

  4. Early flowering plants, modern trees, and modern insects evolve
  5. Several mass extinctions occur including that of the Dinosaurs

IV. Cenozoic Era (Recent Life)

A. Paleocene Epoch

  1. 65—55 million years ago vast inland seas dry up, exposing large land areas
  2. Placental mammals eventually dominate the land including primates, ungulates,

Rodents, and carnivores
  1. Eocene Epoch
  1. 55—34 million years ago the Rockies and Alpine-Himalayan mountain systems

    2. Form

  2. The climate is subtropical and moist throughout North America and Europe
  3. Early forms of horse, rhinoceros, camel, and bats evolve
  1. Oligocene Epoch
  1. 34—24 million years ago the climate is generally temperate with glaciations

    2. Beginning in Antarctica

  2. Modern mammals become dominant vertebrate life forms and many archaic

    3. Mammals become extinct

  3. Grasslands expand and forest regions diminish
  1. Miocene Epoch
  1. 24-5 million years ago ocean currents are established, the climate cools, and

    2. Antarctica becomes permanently frozen

  2. Almost half of all modern placental mammal families are present
  3. Almost all modern whale groups are present
  4. Many modern birds—herons, ducks, eagles, hawks, crows, and sparrows are

Present
  1. Pliocene Epoch
  1. 5—1.8 million years ago the Sierra Nevada and Cascade Mountains are formed
  2. Climate becomes drier and cooler
  3. Primates continue to evolve
  1. Quaternary Period

A. Pleistocene Epoch

  1. 1.8 million—10,000 years ago known as the Great Ice Age
  2. As much as 30% of the Earth’s surface is covered by glaciers
  3. The oldest species of Homo—Homo habilis—evolves
  4. Mammalian evolution includes the development of large forms
  5. Large mammals such as horses, camels, and mammoths
  1. Holocene Epoch
  1. 10,000 years ago—present the glaciers retreat, climate warms, and deserts

    2. Form in some areas

  2. Homo sapiens evolve and human civilization develops
  3. Human activity begins to affect world climate
  4. Other species continue to become extinct

 

 

 

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