Geologic Time

A brief history of the 4.6 Billion history of Planet Earth.

The Geologic Time Scale

The standard method used to divide the Earth’s long (4.6 Billion year) natural history into manageable parts.Boundaries indicate visible changes

on Earth or mass extinction events (the

death of every member of a species.)

• Eon – Largest division of time • Era – Unit of geologic time that

includes two or more periods • Period – A unit of geologic time into

which eras are divided• Epoch – A subdivision of a geologic

period

• Most of the evidence is found in the fossil record

Fossil Record• Fossil evidence provides

evidence of the history of life on Earth.– Life likely appeared around

3.5 billion years ago

• Many organisms have gone extinct.

• Fossils form in sedimentary rock over time.

• A large amount of the fossil record/geologic record is incomplete! (over 25%)

What are Fossils?• Physical evidence preserved by geologic processes mentioned

before by creating correlations (rocks of a similar age compared across regions.)

• Type of fossil is formed based upon the conditions in which it died and was buried.

• Best specimens are those who had rapid burial and possession of hard parts.

• Are found in…– Sedimentary Rocks. Slows decay, preserves hard parts of

organisms (i.e. shells, bone)– Amber. Hardened Tree Sap. Best preserved fossils.– Petrifaction. Minerals replace an organism’s tissues.– Asphalt. La Brea deposits in LA are 38,000 years old.– Frozen. No decomposing bacteria. In 1999, found a 20,000 year

old wooly mammoth in Siberia.

Eon Highlights• Hadean Eon (4.6 billion – 3.8 billion) The only

rocks that scientists have found are meteorites and rocks from the moon.

• Archean Eon (3.8 billion – 2.5 billion) The earliest known rocks on Earth formed during this eon.

• Proterozoic Eon (2.5 billion – 543 million) The first organisms with well developed cells appearing during this eon.

• Phanerozoic Eon (543 million – present) The rock and fossil record mainly represents the Phanerozoic eon, which includes the diverse species of our time.

Era Subdivision• PALEOZOIC – (543 to 248 MYA) It is the first era well

represented by fossils. It is known as the Age of Marine Life, where slowly life moved onto land (flowering plants, amphibians)– This era ended with the largest mass extinction in history, 90% of all

species died.– Likely due to a change in the temperature of the oceans.

• MESOZOIC – (248 MYA to 65 MYA) This era is known as the Age of Reptiles because reptiles (dinosaurs) ruled the land. At this time, small mammals and birds evolved.– This era ended with a large mass extinction where 15% to 20% of all

species died including all dinosaurs. – Likely due to global climate change (asteroid?)

• CENOZOIC – (65 MYA to present day) Known as the Age of Mammals who proved to be the most fit to the new environment with endothermy, internal fertilization and bearing live young with parental care.

Precambrian (4.6 Billion years ago to 543 million years ago.)

• Longest time period of geologic history.

• Until the discovery of soft-bodied organisms in Australia in 1947, paleontologist believed that only single-celled microorganisms and blue-green algae (prokaryotes) lived during this period.

• In the Precambrian seas there lived primitive jellyfish, annelids, and arthropods.– (590-700 million years ago.)

Precambrian

Paleozoic: Cambrian Period (543-490)

• Invertebrates with hard parts (fossils from the Burgess Shale) mark the end of the Precambrian and the beginning Cambrian. – Shells, skeletons, legs and sensing anntenae.

• Life sprung up in abundance, little mountain building or volcanic activity.

• Continental collisions resulted in environmental changes. Gondwana rifted apart (long belt of volcanism near present Appalachian mountains) with landmasses located near the equator.

Cambrian Critters

Paleozoic: Ordovician Period (490-443)

• The first fish appeared in warming seas.

• Coral reefs appeared and created extensive chain of islands and habitats.

• Plants absorbed increased amounts of CO2, lessening the “Greenhouse Effect” and cooled the Earth to create an ice age (440 MYA)

• North Africa was directly over the South Pole and an era of mountain building due to plate collisions in North America.

Ordovician

Paleozoic: Silurian Period (443-417)

• Land plants have established on previously barren continents. Development of vascular systems in trees (taller plants)

• Ozone layer sufficient protection against UV rays (formed in the late Precambrian)

• Huge Insects move to the shores, Centipedes and Spiders!

• Northern Continents collided to form Laurasia and was separated from Gondwana by the Tethys Sea.

Silurian

Paleozoic: Devonian Period (417-354)

• A warmer climate has permeated throughout the world, widespread deserts, evaporates, coral reefs and coal deposits.

• Age of Fishes: All type of fish

• Laurasia and Gondwana approaching and closing off the Tethys Sea. Heavy time of asteroid or comet bombardment. (Evidence: Iridium layer)

Devonian

Paleozoic: Carboniferous Period (354-290)

• Includes the Mississippian and Pennsylvanian Periods.

• Major coal deposits were formed during the Pennsylvanian.

• Ferns flourished, and saw the beginning of true trees with seeds and woody plants.

• Amphibious fish came onto the land. (evolved tongues to catch prey!)

• Extensive forests and swamps, first trees with roots.

Paleozoic: Permian Period (290-248)

• Important reserves of oil and natural gas reside in the Permian basins (Asia, Africa, North America and Australia.)

• Pangaea Forms: Widespread mountain building and volcanism. Large interior lands were deserts, leading to a decline in fish & amphibians.– The most fossils (highest organic burial rate

in history)– Appalachian Mountains (350-250 MYA) &

Urals– Tethys Sea closed

• End of the Permian had the greatest amount of species eliminated (90-95%) and paved the road for reptiles to dominate the landscape.

Mesozoic: Triassic Period (248-206)

• In many ways, the Triassic was a time of transition. • It was at this time that the world-continent of Pangaea

existed, altering global climate and ocean circulation.• The Triassic also follows the largest extinction event in

the history of life, and so is a time when the survivors of that event spread and re-colonized.

• Reptiles emerged as the clear dominant species and types: Turtles, crocodiles, dinosaurs.

• The Petrified National Forest has come from this time where large conifers became buried in these river sediments.

Mesozoic: Jurassic Period (206-144)

• Dinosaurs radiated rapidly and filled most of the niches and gaps in the environment.

• The Super-continent of Pangaea has broken apart into separate, wandering continents.

• Ferns, cycads and gymnosperms dominated the flora.• Named for the Jura Mountains on the border between

France and Switzerland, where rocks of this age were first studied.

• The Jurassic is still important to us today, both because of its wealth of fossils and because of its economic importance -- the oilfields of the North Sea, for instance, are Jurassic in age.

Jurassic Period

Mesozoic: Cretaceous Period (144-65)

• During this time vast and ubiquitous limestone deposits known to geologists as "The Chalk" were deposited in many parts of the world.

• This "Chalk" is most dramatically exposed in what are well known as "the white cliffs of Dover" in England.

• As for the term "Cretaceous" it is derived from the Latin 'creta' meaning 'chalk'.

• The first fossils of many insect groups, modern mammal and bird groups, and the first flowering plants.

Cenozoic: Tertiary Period (65-1.8) • Includes the Paleocene, Eocene, Oligocene, Miocene,

Pliocene epochs.• A Cooling Trend From Tropics To Ice Age

The beginning of the Tertiary Period was very warm and moist compared to today’s climate.– Much of the earth was tropical or sub-tropical. – Palm trees grew as far north as Greenland.– The plants of the Tertiary Period are very similar to the

plants that we have today. Dense, swamps, forests and grasslands.

– Era of Mammals, especially grazing animals.– By the middle of the tertiary, during the Oligocene Epoch,

the climate began to cool. This cooling trend continued and by the Pliocene Epoch at the end of the Tertiary Period, an ice age had begun.

Cenozoic: Tertiary Period

Cenozoic: Quaternary Period (1.8-present)

• Includes the Pleistocene and Holocene Epochs• The Quaternary period saw the global temperature

continue to fall, culminating in what is known as the Ice Age.

• Actually there is not one Ice Age but a whole series of glacial periods (principally in the Northern Hemisphere) interspersed by warm, even tropical, inter-glacials.

• This marked climatic oscillation is superimposed on the long-term global cooling that began in the mid-Tertiary. The most recent cycle ended only about 12,000 years ago.

• Modern Humans dominated this period.

Quaternary Period