Transcript Geologic Time - Honors Earth and Environmental Science

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.)
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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
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 bluegreen 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