IT IS ESTIMATED THAT THE EARTH FORMED
ALONG WITH THE SOLAR SYSTEM 4.6 BILLION
YEARS AGO (4,600 MYA)
GEOLOGIC TIME SCALE
A SUMMARY OF THE MAJOR EVENTS IN EARTH’S HISTORY
EON – largest segment of geologic time
ERA
PERIOD
EPOCH – smallest segment of geologic time
RELATIVE TIME
VS.
PLACES EVENTS IN A
SEQUENCE BUT DOES
NOT IDENTIFY THEIR
ACTUAL DATE OF
OCCURRENCE
ABSOLUTE TIME
IDENTIFIES THE ACTUAL
DATES OF GEOLOGIC
EVENTS
EXAMPLE
A LIST IN
CHRONOLOGICAL
ORDER OF WHAT YOU
HAVE DONE TODAY UP
UNTIL THIS TIME
THE EXACT TIMES AT
WHICH YOU DID
THESE THINGS
LAW OF SUPERPOSITIONIN UNDISTURBED
SEDIMENTARY ROCKS THE
OLDEST ROCK LAYERS
ARE AT THE BOTTOM AND
THE YOUNGEST ARE AT
THE TOP.
LAW OF CROSS-CUTTING RELATIONSHIPSAN IGNEOUS INTRUSION IS YOUNGER THAN
THE ROCK IT HAS INTRUDED INTO.
LAW OF INCLUDED FRAGMENTS - IF FRAGMENTS
OF ONE TYPE OF ROCK ARE FOUND IN ANOTHER
ROCK LAYER THE ROCK FRAGMENTS MUST BE
OLDER THAN THE ROCK LAYER IN WHICH THEY
ARE FOUND
FAULTED AND FOLDED LAYERS - LAYERS OF
ROCK THAT HAVE BEEN FAULTED OR FOLDED
MUST HAVE BEEN PRESENT BEFORE THE ACTIONS
OF FAULTING OR FOLDING TOOK PLACE
FOLDING
FAULTING
UNCONFORMITY- A PLACE IN THE ROCK RECORD WHERE
LAYERS OF ROCK ARE MISSING BECAUSE OF UPLIFT AND
EROSION. THE RESULT CAN BE A LARGE AGE
DIFFERENCE BETWEEN THE ROCKS ABOVE AND THOSE
BELOW THE EROSIONAL SURFACE (IT APPEARS LIKE A
SQUIGGLY LINE IN A CROSS-SECTION)
PLACE THE FOLLOWING EVENTS IN ORDER STARTING
WITH THE OLDEST.
E
L
B
I
G
K
M
F
A
C
D
H
J
MATCHING OF ROCK
LAYERS THAT CAN BE SEEN
AT THE EARTH’S SURFACE,
OVER A LARGE AREA
AN OUTCROP IS EXPOSED
ROCK LAYERS AT THE
EARTH’S SURFACE
A KEY BED IS A THIN, WIDESPREAD LAYER, USUALLY OF
VOLCANIC ASH, THAT CAN BE USED TO CORRELATE AN
EXACT POINT OF TIME
A FOSSIL IS ANY EVIDENCE OF EARLIER LIFE
PRESERVED IN THE ROCK
ORIGINAL REMAINS (RARE) – THE ACTUAL
UNCHANGED REMAINS OF THE PLANT OR
ANIMAL ARE PRESERVED.
REPLACED REMAINS – THE SOFT PARTS OF THE
ORIGINAL ANIMAL HAVE DISAPPEARED AND THE
HARD PARTS HAVE BEEN REPLACED BY MINERAL
MATERIAL. (PETRIFIED WOOD)
MOLDS AND CASTS – FOSSIL SHELLS OR BONES ARE
DISSOLVED COMPLETELY OUT OF THE ROCK LEAVING
A HOLLOW DEPRESSION IN THE ROCK. NEW MINERAL
MATERIAL FILLS THE MOLD IT FORMS A CAST OF THE
ORIGINAL FOSSIL.
TRACE FOSSILS – EVIDENCE OF
LIFE OTHER THEN REMAINS,
WHICH INCLUDES ANY
IMPRESSIONS LEFT IN THE ROCK.
(TRAILS, FOOTPRINTS, TRACKS,
BURROWS)
INDEX FOSSIL
EASILY IDENTIFIABLE
SHORT-LIVED
WIDESPREAD OCCURRENCE
MEASURING ABSOLUTE TIME
TREE RINGS
EACH RING REPRESENTS A SINGLE
YEAR (SPRING/FALL) THE WIDTH OF THE
RING DEPENDS UPON THE
TEMPERATURE AND RAINFALL
VARVES
GLACIAL LAKE DEPOSITS. A THICK
LIGHT COLORED LAYER IN THE
SUMMER AND A THIN DARK LAYER
IN THE WINTER
RADIOACTIVE DATING
USED TO DATE FAR BACK IN TIME. CERTAIN ROCKS CONTAIN
RADIOACTIVE ISOTOPES
RADIOACTIVE ISOTOPES ARE ATOMS OF
ELEMENTS THAT GIVE OFF RADIATION FROM
THEIR NUCLEI
RADIOACTIVE DECAY IS THE PROCESS BY
WHICH A RADIOACTIVE ISOTOPE CHANGES
INTO A NEW STABLE ELEMENT
THE RATE AT WHICH A RADIOACTIVE ELEMENT DECAYS. IT
IS THE TIME IT TAKES FOR HALF OF THE ATOMS OF THE
RADIOACTIVE ELEMENT TO DECAY TO A STABLE END
PRODUCT (SEE PAGE 1 OF THE ESRT)
AT THE END OF EACH HALF-LIFE, HALF OF THE
RADIOACTIVE MATERIAL REMAINS
PARENT ISOTOPE = THE RADIOACTIVE ISOTOPE THAT BEGINS
DAUGHTER ISOTOPE = THE STABLE ISOTOPE THAT HAS BEEN CHANGED
RADIOCARBON DATING
USES THE RADIOACTIVE ISOTOPE CARBON-14
FOUND IN ALL LIVING THINGS.
BECAUSE CARBON-14 IS CONTINUALLY ABSORBED BY FOOD
AND WATER IT STAYS CONSTANT IN LIVING THINGS.
WHEN THE LIVING THING DIES THE PERCENTAGE OF
CARBON-14 DECREASES AT THE RATE OF ITS HALF-LIFE.
CAN BE USED TO DATE BACK ABOUT 100,000 YEARS
URANIUM LEAD METHOD IS USEFUL TO DATE ROCKS
OLDER THAN 10 MILLION YEARS. CAN BE USED ONLY ON
IGNEOUS ROCKS THAT CONTAIN THE RIGHT KIND OF
URANIUM
RUBIDIUM-STRONTIUM METHOD CAN ALSO BE USED
TO DATE OLDER ROCKS BECAUSE OF ITS LONG HALF-LIFE. IT
IS ALSO VERY COMMONLY FOUND IN IGNEOUS ROCKS.
POTASSIUM-ARGON METHOD IS VERY USEFUL SINCE
POTASSIUM-40 CAN BE FOUND IN METAMORPHIC,
SEDIMENTARY, AND IGNEOUS ROCKS. IT CAN DATE OLDER
ROCKS BUT MAY ALSO DATE ROCKS AS YOUNG AS 50,000
YEARS
Divisions of Geologic Time
• Eras are subdivided into periods...periods are
subdivided into epochs.
Era
Period
Epoch
E + P = EP
Divisions of Geologic Time
• Geological time begins with Precambrian
Time. Precambrian time covers
approximately 88% of Earth’s history.
FOUR Eras…
• PRE-CAMBRIAN – 88% of earth’s history
• Paleozoic (ancient life)
– 544 million years ago…lasted 300 million yrs
• Mesozoic (middle life)
– 245 million years ago…lasted 180 million yrs
• Cenozoic (recent life)
– 65 million years ago…continues through present day
Paleozoic Era (Ancient Life)
• The Cambrian period is the 1st period of the Paleozoic Era.
“Age of the Trilobites”
• Explosion of life in the oceans began during this era.
• Most of the continents were covered in warm, shallow seas.
– Invertebrates were dominate - Trilobites
– Fish emerged during this time
– Fish led to the arrival of amphibians
• The end of the Paleozoic era is called the “Age of Amphibians”
– Early land plants including mosses, ferns and cone-bearing plants.
– The early coal forming forests were also formed during this time.
Paleozoic Era
• Much of the limestone quarried for building and
industrial purposes, as well as the coal deposits of
western Europe and the eastern United States, were
formed during the Paleozoic.
• The Cambrian (beginning) opened with the breakup
of the world-continent Rodinia and closed with the
formation of Pangaea, as the Earth's continents came
together once again.
– This event is thought to have caused the climate
changes that led to mass extinction event.
• The Appalachian mountains were formed during this
time.
Paleozoic Era
• At the end of the Paleozoic, the largest mass
extinction in history wiped out approximately
90% of all marine animal species and 70% of land
animals.
– Possible causes of this Mass Extinction Event
• Lowering of sea levels when the continents were
rejoined as Pangaea (convergent boundary)
• Increased volcanic activity (ash and dust)
• Climate changes – cooler climate
Trilobites
• Lived in Earth’s ancient seas
• Extinct before the dinosaurs came
into existence
• Cambrian Period is know as the
“Age of the Trilobites” (put in
on table)
Brachiopods
• Marine animals that resemble clams.
Early Fish
Early fish did not have
jaws.
Some species of sharks
were in existence at
this time.
Frilled Shark that was found in Japan in January 2007. This
shark was considered a “living fossil”
Early Land Plants
Mosse
s
Cone bearing plants
Fern
Mesozoic Era – Middle Life
• At the beginning of this era the continents
were joined as Pangaea.
• Pangaea broke up around the middle of this
era.
• Reptiles became the most abundant animals
because of their ability to adapt to the drier
climate of the Mesozoic Era.
– Skin maintains body fluids
– Embryos live in shells
Mesozoic Era
• Dinosaurs were also very active in this era.
– First small dinosaurs appeared in the Triassic
Period.
– Larger and more abundant dinosaurs appeared in
the Jurassic Period.
• Small mammals and birds also appeared
during this era.
– The mammals were small, warm-blooded animals.
Hair covering their bodies.
• These characteristics help them survive in changing
environments.
Mesozoic Era
• The main plant life of this time were
Gymnosperms or plants that produce seeds, but no
flowers.
– Pine Trees
• Flowering plants appeared during the END of this
era.
Mesozoic Era
• This era ended with a mass extinction event about
65 million years ago.
– Many groups of animals, including the dinosaurs
disappeared suddenly at this time.
• Many scientists believe that this event was caused
by a comet or asteroid colliding with the Earth.
Crater sites on Earth
Mesozoic Era – Mass Extinction Event
• Asteroid or Comet collides with Earth.
–
–
–
–
–
Huge cloud of smoke and dust fills the air
Blocks out sunlight
Plants die
Animals that eat plants die
Animals that eat plant-eaters die.
• However, not all forms of life died during this event.
Many animals that you see today are descendants
from the survivors of this extinction event.
Mesozoic Reptiles
Mesozoic Mammals
Mesozoic Plants
Flowering plants
evolved towards the end
of the Mesozoic Era.
Cenozoic Era – Recent Life
• Began about 65 million years ago and continues today!!!!!
– Climate was warm and mild.
– Marine animals such as whales and dolphins evolved.
• Mammals began to increase and evolve adaptations that
allowed them to live in many different environments – land,
air and the sea.
– Grasses increased and provided a food source for grazing animals
• Many mountain ranges formed during the Cenozoic Era
– Alps in Europe and Himalayas in India; Rocky Mountains in the
USA
Cenozoic Era
• Growth of these mountains may have helped to cool
down the climate
– Ice Ages occurred late in the Cenozoic Era (Quaternary
Period).
• As the climate changed, the animals had to adapt to
the rise and fall of the oceans caused by melting
glaciers.
• This era is sometimes called the “Age of Mammals”
Cenozoic Era
• Marine animal examples:
– Algae, Mollusks, Fish and Mammals
• Land animal examples:
– Bats, Cats, Dogs, Cattle and Humans
– Humans are thought to have appeared around 3.5 million
years ago (during the most recent period – Quaternary).
• Flowering plants were now the most common plant
life.
Cenozoic Mammals
Flowering Plants were common
during the Cenozoic Era