Transcript Excite-Making a Time Scale of Your Year

Geologic Time Test
• I can/can do/will know….(see the pink writing on the slides)
– List how old the Earth is
slide 2
– Explain how the start and endings of the divisions on the
Geologic Timeline are determined.
slide 2
– Explain how scientists know all about Earth’s past slide 5
– Define what an index fossil is and how it is a slam dunk in
determining the age of a rock layer.
slide 5
– Place in order, by length, the time spans:
Epoch, Era, Eon, and Period. (longest to shortest)
slide 6
– Explain how an organism's size/complexity tells us about its
position on the Geologic Timeline.
slides 7-12
– List what eon and era we live in
slides 8 &12
– When the dinosaurs disappeared and why
slide 10
– Given fossil evidence, make conclusions about what events
have taken place in history.
slide 11
Geologic Time Scale
• Helps us study Earth’s pastwhich is really old
(estimated 4.6 billion years old)
• Divides Earth’s history into
intervals of time determined by
--major events/changes in the rock layers, and
--the appearance/disappearance of fossils/life
Slow Changes on our Earth
•Mountain forming
•Climate
•Erosion
•Weathering
Fast Changes on our
Earth
• Volcanic
Eruptions
• Earthquake
• Flood
How do we know what has
happened all this time?
• Fossil information
– Tells us what life existed when
• Rock layers/sequencing
– Tells the relative age & what the environment was like
• Index fossils have a wide distribution world-wide, live for a
short period of time in one particular time span, and help date
the layer(s) they are found in.
• Fossilized seashells found in the mountains tells us that there
was no mountains there long ago, just seafloor.
• Fossilized corals on land indicates that a previous ocean
environment existed there.
Divisions & sizes of
Geologic Time spans
• Eon-largest unit of time (Earth’s history has four
eons)
• Era- A division of an Eon. The most recent eon is
divided into three eras: Paleozoic, Mesozoic, and
Cenozoic.
• Periods-Each era is subdivided into a
number of
periods.
• Epoch- The periods of the Cenozoic, the most
recent era, are further divided into epochs
“Pre-Cambrian Time”
• Makes up 90% of Earth’s History
• Hadean, Archean, and Proterozoic eons
make up the Pre-Cambrian Time
• Fossil record dominated by tiny, single
celled organisms that can only be seen
with a microscope (bacteria) and soft
bodied animals that didn’t fossilize
(like jellyfish)
• Earth cooled, continents formed
Phaneorozoic Eon
(our current eon)
•Divided into 3 Eras:
•Paleozoic- “ancient life”
•Mesozoic- “middle life”
•Cenozoic- “recent life”
Paleozoic Era
• 542 mya to 251 mya
• All life lived in the ocean at the start. Multi-celled life
• Early Paleozoic =Age of the Invertebrates
• Middle Paleozoic =Age of the Fishes
Vertebrates & insects evolve and first plants
• Late Paleozoic =Age of the Amphibians
Life started to move on land. Reptiles evolve.
Pangaea and mountain ranges form
• Mass extinction happened at the end (248 mya)90% of all species perished.
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Mesozoic Era
250 mya to 65 mya
Bigger and more complex life
Age of the Reptiles (dinosaurs dominate)
Pangaea breaks up
Sm. mammals, birds, and flowering plants first
appeared & evolve.
• N. America covered by a sea
• A mass extinction event (asteroid?) 65mya killed
off 50% of all species (& the dinosaurs)
– from the heat at the impact site,
– lack of sunlight and thus photosynthesis world-wide, &
– other catastrophic impact effects (tsunamis, earthquakes, etc)
KT Asteroid
• Is thought to have
caused the mass
extinction of the
dinosaurs as
evidenced by the
lack of fossil size &
diversity afterwards
• Happened 65
million years ago
Cenozoic Era
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65 mya to present day (our current era)
Age of Mammals –biggest and most complex life
Ice Age happened during this time
Mammoth, saber-toothed cats and other
large mammals common during the first part
of this time are now extinct
• End of era natural land bridges allowed first
humans and animals to spread around the
planet.