Geologic Time Scale

• Shows significant events in the history of earth and of the evolution of living things

• Were able to develop this timescale by studying rock layers and index fossils worldwide which made it possible for the to identify the relative age of earth. (4.5 billion years)

Ways Archaeologists Tell The Age of Sites and Artifacts

• Absolute Dating

  • Provides a specific calendar year for the occupation of a site.

• Relative Dating

  • Tells how old something is in relation to other objects but cannot provide a year or specific date of use.

  • Estimate whether an object is younger or older than other things found at the site

• Radioactive Dating

  • A method of dating rocks and minerals using radioactive isotopes.

Eon/Eonothem

• The largest/longest divisions in the geologic timeline

Eras/Erathem

• Smaller division within Eons

Periods “Systems”

• Further subdivisions in eras

Epochs “Series”

• Finer subdivisions in Cenozoic and some parts of the Mesozoic era.

The Geologic Time Scale in Reverse Chronological Order

Phanerozoic Eon “Visible Life”

• Cenozoic Era “Recent/Modern Life” / “Age of Mammals”

• Quaternary Period “Rise of Man”

• Holocene (Recent Epoch)

• Historical time

• Pleiostocene

• Ice ages and origin of Homo

• Neogene Period “Upper/Later Tertiary”

• Pliocene

• Bipedal humans appear

• Miocene

• Mammals and Angiosperms continue to diversify

• Paleogene Period “Earlier Tertiary”

• Oligocene

• Origin of primates

• Eocene

• Angiosperms dominate and mammals diversify

• Paleocene

• Mammals, birds, and insects diversify

• Mesozoic Era “Middle Life”

• Time of the Dinosaurs and Age of Reptiles

• Pangaea started to break apart

• Cretaceous

• Angiosperms diversify and dinosaurs extinct

• Jurassic

• Dinosaurs abundant, first birds appear, gymnosperms dominate

• Triassic

• Dinosaurs evolve, origin of mammals, gymnosperms dominate

• Paleozoic Era “Ancient Life”

  • Permian Period “First Reptiles

• Reptiles diversify, major extinction of many marine organisms

• Carboniferous Period

• First seed plants appear, origin of reptiles, and amphibians dominate

Two Parts

• Pennsylvanian

• First Insects

• Missisipian

• Many Crinoids/ Marine animals

• Devonian Period “Age of Fishes”

• Bony fishes diversify, insects, and first amphibians appear

• Silurian Period “First Land Plants”

• First vascular plants appear

• Ordovician Period “Age of Invertebrates”

• Fungi, plants, and animals colonize land

• Cambrian Period

• Marks an important point in the history of life on earth

• Time when major groups of animals first appear in fossil record

• First fish, many animal phyla diversify (Cambrian Explosion)

THE PRE-CAMBRIAN TIMES (88% of Earth’s Geologic Time)

Protozoic Eon “Longest Geologic Eon”

• Ediacaran Period

• Appearance of Algae and invertebrates

• Oldest fossils of Eukaryotic cells

• Carbonate rocks abundant

Archaean Eon “Earliest period in Geologic period”

• Atmospheric oxygen concentration increases

• Oldest fossils of cells (Cynobacteria)

• Oldest known rocks (Acasta Gneiss)

Hadean Eon “Oldest Eon” 

• Earthworms

Terms in The GEOLOGIC Timescale

• Ka / Kilo annum

• One thousand years

• Ma / Mega annum

• One million years

• Ga / Giga annum

• One billion years

Mechanisms that Produce Change from Generation to Generation

Natural Selection

• Concept of fitness is the central process of evolution by natural selection

• Fitness is an individuals ability to survive and reproduce in a specific environment.

• Individuals with characteristics not suited to the environment will die off, whereas those with characteristics will pass these on to their offspring

• Ex. of Environmental Pressures

• Overpopulation, Resource Competition, Changing Environments, Predators

• Produces organisms with improved body structures for their habitats

• Present-day organisms are different from their ancestors due to the Principle of Descent with Modification

• Ex. Raphus cucullatus/Dodo bird

• Found in Mauritius in the Indian Ocean, East Madagascar.

• Were nonflying and overweight allegedly unfit to their environment since this made them easy prey

• Obesity, slowness, and lack of intelligence are cited as reasons for their extinction

Types of Natural Selection

Stabilizing Selection

• An average phenotype is favoured compared to extreme phenotypes

• Ex. Robins lay 4 eggs because if they lay more they lack resources however if they lay less some will not hatch.

Directional Selection

• A change in the environment shifts the spectrum of phenotypes observed

• Happens when one extreme trait is favoured over the other

• Ex. Big seeds are common so birds with bigger beaks will survive better.

• Ex. Giraffe’s Neck

Diversifying/Disruptive Selection

• Two or more extreme phenotypes are selected for, while the average phenotype is selected against

Artificial Selection

• Humans can select variations between different organisms that are useful to them

• Done through Selective Breeding

Selective Breeding

• Involves choosing parents with particular characteristics to breed together and produce offspring with more desirable characteristics

• Breeders are able to produce a wide range of plants and animals that look very different from their ancestors.

Non-Random Mating

• Contributes to the population change from one generation to the next

• Is the selected probability of mating with another individual in a population

2 Forms of Non-Random Mating

• Inbreeding

• When individuals are more likely to mate with a close relative than a distant relative

• Close Breeding

  • When animals are very closely related and can be traced back to more than one common ancestor

• Outbreeding “Assertive Mating”

• Happens when individuals select distant relatives more than close relatives

• Crossbreeding

  • The mating of two different animals of different breeds

  • Hybrid Vigor/Heterosis is the name of superior traits in the crossbred progeny

• Grading Up

  • Wherein the animals of an indigenous breed is mated to an improved pure breed for several generations to attain the superior traits of the improved breed

  • Continuous use of purebred sires of the same breed in a grade herd.

  • By fifth generation, the graded animals may reach almost purebred levels.