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Geologic Time 2
Transcript of Geologic Time 2
(or Earth's teen years)
Scientists use geologic time because Earth is SO OLD we could NEVER
use centuries etc. to describe events
1st developed by Scientists by studying rock layers & fossils
they put these in order by relative age (generally oldest to youngest)
then using radioactive dating and other methods they could
sort them by absolute age & made the divisions of time
Divisions are based on changes in life forms
Divisions of geologic time
Earth was new - HAPPY BIRTHDAY!
1st Stop - PRECAMBRIAN TIME
(or...Earth's baby years)
as new life forms emerged and others disappeared
like marking special events in your life (toddler years, elementary school years, middle school etc.
Precambrian - longest = 88% of Earth's "Life"
Eras (Paleozoic, Mesozioc and Cenozoic)
Era > Period > Epoch
gravity pulled Earth's materials together and over time the inside became very hot, liquid rock
over millions of years, lava flowed from volcanoes and the continents were made
the atmosphere formed and Earth was covered in water
or Earth's toddler years
means ancient(paleo) life(zoic)
lasted from 542mya - 251mya
was marked by an 'explosion' of life;
called the "Cambrian Explosion"
so many different organisms evolved
all animals lived in the seas
invertebrates(jellyfish & sponges)
plants now grow on land in low, damp areas
1st insects appear
coral reefs develop
fish with jaws are present
Precambrian Time Cont'd
No one knows exactly where or when life actually began
the earliest fossils are from about 3.5 bya!
they were of single-celled organisms
all life evolved from these 'bacteria'
organisms that can perform photosynthesis
exist starting about 2.5 bya
(things like sponges and worms)
most were soft-bodied so there are very few fossils
1st vertebrates evolved (jawless fishes)
ancestors of today's octopus & squid
Earth was covered with warm, shallow seas
small reptiles are present
amphibians are also present
winged insects become abundant
giant ferns and other trees form 'coal forests'
Appalachian Mountains form
mass extinction (signifies the end of the Paleozoic Era
95% of all life forms in the ocean disappear (become extinct)!
many reptiles & fish DO SURVIVE!
one hypothesis for the cause of the mass extinction is severe and abrupt climate change caused by the formation of Pangaea
dinosaurs are the dominant animal on land
larger dinosaurs especially thrive
reptiles & dinosaurs are still dominant
mammals continue to evolve
flying reptiles become extinct
flowering plants evolve
continents are close to their present-day locations
1st snakes appear
means middle(meso) life(zoic)
from 245 - 65 million years ago
Age of Reptiles
reptiles were very successful
1st dinosaurs appeared
1st mammals appeared; small like a mouse or shrew
these probably evolved from warm-blooded reptiles
1st turtles and crocodiles appear
1st birds appear
may have evolved from dinosaurs
Pangaea breaks apart (North America separates)
The end of an era...
there was another mass extinction (about 65 mya)
may have been caused by an asteroid striking Earth
may have been caused by volcanic activity which in turn would have cause dramatic climate change
volcanoes would have blown dust and created heavy clouds which blocked sunlight for YEARS!!!
NO dinosaurs survived
many reptiles also became extinct
because many plants died, all life above plants on the food chain was affected
(or Earth's adult-hood)
means recent(ceno) life(zoic)
65mya - ?
Earth's climate cooled, causing a series of ice ages
glaciers would repeatedly form and melt over parts of Europe and N. America
as a result, sea levels would drop and rise
Earth had warm, mild climates
marine mammals (whales & dolphins) evolved
the appearance of grass provided food for the ancestors of today's cattle, deer and sheep
mammals and birds grew large
The Age of Mammals
the extinction of the dinosaurs created an opportunity for mammals
decreased competition for resources and threat from predators
current mammals (bats, cats, dogs, cattle and HUMANS) were common
modern humans evolve in Africa somewhere around 100,000 years ago
The evolution of HUMANS!!!!
Also known as the "Age of Fishes"
animals begin to invade land
lungfish come onto land and amphibians evolved
sharks appear near the end of the period
also, many rocks were deeply buried and changed by heat and pressure