Transcript A trip through Geologic Time

A TRIP THROUGH GEOLOGIC TIME
Fossils
Fossils- preserved remains or traces of living things
**For fossil to form we the organism NEEDS to have hard parts
ex. Bone, shells, teeth, seeds woody stems
1.) The organism dies
2.) It is buried by sediment
3.) the sediment hardens into rock and preserves the shape of the organism
**Many organisms that become fossils live in or near quiet water (swamps, lakes or shallow seas)
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Types of Fossils
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Molds and Casts (most common)
• Molds-hollow area in sediment in the shape of an organism, organism is buried then decays
• Cast-solid copy of the shape of an organism, formed when water deposits minerals in a mold
• BOTH can preserve fine detaills
•
Petrified fossils- minerals replace all of an organism (tree) or part (dinosaur bone)
• petrified = turned into stone
•
Carbon films- extremely thin coating of carbon on a rock produced
when gases escape from sediment that is covering an organism
• can preserve delicate part of plant leaves and insects
•
Trace Fossils- provide evidence of the activities of ancient organisms, ex. Footprint, trails, burrows,
coprolite, eggs and nests
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Preserved Remains• Sticky tar
• Tree resin produces amber (hardened tree sap) which traps organisms
• Freezing
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Paleontologists- scientists who study fossils
Fossil Record- all of the information that paleontologists have gathered about past life
**provides evidence about
1.) how life has changed over time
2.) what past environments were like
3.) how the Earth’s surface has changed
Past Environments
•
Fossils can tell how much water in an area and what type of water is in an area (bay, ocean bottom,
swamp)
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Fossils can indicate what past climate was like
ex. Coal found in Antarctica
-- coal only forms from plants that grow in warm, swampy regions
--this shows that the climate of Antarctica used to be warmer than it is today
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The Relative Age of Rocks
Relative Age-Age compared to the other things around it
Absolute Age-number of years that have passed since the rock was formed
**Fossils are most often found in sedimentary rock
Law of superposition-geologic principle that states that in undisturbed horizontal layers of sedimentary
rock, each layer is older than the layer above it and younger than the layer below it
**More simply—the oldest layer is on the bottom and the youngest is on the top
Index Fossils- Fossils of widely distributed organisms that lived during a geologically short period, they
are useful because they tell the relative age of the rock layers in which they occur
**Scientists infer that layers with matching index fossils are the same age
Match the rock layers in locations
2, 3, and 4 with first area shown.
Which fossils can be
used as index fossils?
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Clues from Faults and Folding
Fault- a break in Earth’s crust due to forces inside Earth which causes movement of the rock on opposite
sides
**A fault is ALWAYS younger than the rock that it cuts through
Folding:
•
Sometimes forces inside Earth fold layers so much that the layers are turned over
• The youngest layers might end up on the bottom
• folding is younger that the youngest rock affected
• If they are folded into a syncline the youngest rocks are in the core of the fold
• The opposite is true for an anticline
Unconformity- the surface where new rock layers meet old rock layers; a gap in the geologic
record that shows where rock layers have been lost due to erosion
**When rock layers erode away, an older rock surface may exposed, it may erode itself
then deposition begins again building new rock layers
**Due to erosion, most of the geologic rock layers and evidence in them has been lost
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Clues from Igneous Rocks:
Extrusion-lava that hardens on Earth’s surface and forms igneous rock (rock that is formed from magma)
**An Extrusion is always younger than the rock below it\
**Lava flow may cause contact-metamorphism with the older rocks they lie upon
Intrusion-magma that pushes into bodies of rock below Earth’s surface and hardens
**An Intrusion is always younger than the rocks around or beneath it
**An intrusion may produce contact metamorphisms along their contacts with older rocks
The diagram below shows rock layers found at a site.
Identify the area on the diagram that shows an intrusion.
What is the oldest layer of rock in the diagram?
Clues from Metamorphic Rock:
Metamorphic Rocks are preexisting rocks that have been metamorphosed by heat and pressure. If they are in
contact with layered or un-metamorphosed rock they are usually the oldest in the sequence (If those rocks in
contact were there when the metamorphism happened, they too would have been metamorphosed.)
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Unconformities and Folding
What are the oldest and youngest layers in the last two diagrams? Identify the unconformity.
Which is the part of the fold that is overturned?
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Lets see if we can figure out the sequence of events:
List in order the layers from oldest to youngest
1.)
2.)
3.)
4.)
5.)
Now try the examples in your packet.
If you think you have mastered it, try the one on the following slide 
A TRIP THROUGH GEOLOGIC TIME
Put the layers in order from oldest to youngest
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Radioactive Dating
Isotope-Atoms of the same element can have different numbers of neutrons; the different possible
versions of each element are called isotopes
Example: Carbon-12
Carbon12
Carbon13
Carbon14
6
6
6
Electrons 6
6
6
Neutrons 6
7
8
Carbon-14
The number after carbon indicates
the mass number (protons + neutrons) for that isotope
Protons
Radioactive Decay-the process in which the nuclei of radioactive elements break down, releasing fast
moving particles and energy
•
During radioactive decay, the atoms of one element (isotope) break down (change) to form atoms of
another element (isotope)
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Radioactive elements occur naturally in igneous rock
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Scientists use the decay rate to determine the rocks age
•
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In the above table, note that the number is the mass number (the total number of protons plus
neutrons).
Note that the mass number may vary for an element, because of a differing number of neutrons.
Elements with various numbers of neutrons are called isotopes of that element.
Parent Element- the original, unstable, radioactive element, decreases through out process
Daughter Element- the resulting, stable, non radioactive product due to radioactive decay, increases
through out process
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Half Life-the time it takes for half of the radioactive atom to decay to the daughter element
**The half life for the radioactive element never changes no matter how much is left
Determining the Absolute Age of Rocks
1.) Scientists determine the amount of radioactive
material in rock
2.) Compare the radioactive amount to the stable
amount
**Potassium-40 is useful in dating ancient rocks
because of its long half life
**Carbon-14 is used to date fossils because all
living things contain carbon.
--cannot be used to date fossils older than
50,000 years because the amount of carbon
left is too small to measure
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•Draw a circle, shade the circle and fill in the chart according to
how it changes as each half life passes
Half life's past
% Parent
Element
% Daughter
Element
0
100
0
1
50
50
2
25
75
3
12.5
87.5
4
6.25
93.75
5
3.125
96.875
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Lets try some practice problems.
1.) You have a fossil that contains Carbon-14, you know that the total mass of that sample was 40mg.
You have determined that there is 30 mg of Nitrogen-14 in the fossil.
Answer the following:
a.) How many half life’s have passed?
b.) This fossil was formed how many years ago?
c.) What percentage of parent element is present?
d.) What percentage of daughter element is present?
2.) You have a sample of rock with an unknown radioactive material in it, but you have information stating
that it was formed 3.9 billion years ago. You know that the parent element is 7.5mg and the daughter
element is 52.5mg.
Answer the following:
a.) What % is the parent element
b.) What % is the daughter element
c.) How many half life’s have passed
d.) What is the parent element, what is the daughter element?
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The Geologic Time Scale
Geologic Time Scale- Record of the geologic events and evolution
of life forms as shown in the fossil record
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Because the time span of Earth’s history are so great, geologists
use the geologic time scale to show Earth’s history
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•
They use evidence from
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Rock layers
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Index fossils
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Radioactive dating
Everyday divisions of time (century, decade, year, month,
week, day) are not helpful due to the age of the Earth
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Major changes in life forms are used to mark where one
unit of geologic time starts and another begins
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Precambrian = 88% of Earth’s history
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Era-three long units of time that divide time after Precambrian
to present (Paleozoic, Mesozoic, Cenozoic)
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Period-Subdivisions of Eras
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Names of many geologic periods come from places
where geologists first described the rocks and fossils for that
period
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Earth's History in a Day
The table shows the times at which some major events would take place. Visualize
each event on the clock diagram.
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Early Earth
Age of Earth
• Scientists dated the oldest rock to 4 billion years old, but think the Earth formed before
that
• Moon formation- young Earth collided with another object, due to this Earth and moon
must be similar in age
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Rocks from moon have been dated at 4.6 billion years old via carbon dating
Earth takes shape
• Scientists think that Earth began as a ball of dust, rock and ice in space.
• Gravity pulled this “junk” together
• As the Earth grew larger, its gravity increased and it pulled in more and more “junk”
• Due to the collision of this material, energy was released which raised Earth’s temp
until it was VERY HOT—to the point where it melted
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Dense materials sank toward the bottom (hence the dense iron core), less dense, molten material
hardened forming crust and mantle
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Early Earth
This artist’s illustration shows Earth shortly after the moon formed. Earth was hot
and volcanic, and contained no liquid water. The moon was much closer to
Earth than it is today. Over time, Earth’s surface began to cool, forming solid
land.
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The Atmosphere:
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First atmosphere composed of light gases- hydrogen and helium
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Solar wind (strong bursts of particles released from the sun) blew away first atmosphere because gravity was not strong enoug h to hold on to it.
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Second atmosphere-CO2, H2O and N added due to volcanic explosions and comets colliding with Earth
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Comet- a ball of dust, gas, and ice that orbits the sun
Development of the Atmosphere
The illustration shows the difference between Earth’s first and second atmospheres. What is the missing information for each
atmosphere?
The Oceans:
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At first = no oceans, Earth was too hot
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All H2O was vapor
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As Earth cooled, water vapor condensed to form rain, which accumulated to form oceans which absorbed much of the CO 2 from the atmosphere
The continents:
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Early Precambrian- Earth’s rock cools and hardens
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500 million years later-continents formed
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Over billions of years, Earth’s landmasses have repeatedly formed, broken apart and crashed together again
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Early Organisms
• When or where life began is unknown for sure
• Single celled organisms is rock that was formed 3.5 billion years ago
• Other life forms arose from these single celled organisms
• 2.5 billion years many organisms started producing food via
photosynthesis which resulted in an increase of O in the atmosphere
• Some of this O changed into O3 which is ozone
• Ozone layer blocks UV rays from sun allowing organisms to thrive on land
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Precambrian Time (not an era) 4.6 billion years ago – 542 million years ago
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Formation of earth 4.6 billion years ago
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4 billion years ago—oceans form, they cover earth
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First sedimentary rocks form 3.8 billion years ago
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Single celled organisms evolve to multicelled near the end of the Precambrian
Paleozoic Era
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Cambrian Period
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Cambrian Explosion-a great number of different organisms evolved, organisms appear
with hard parts—shells and outer skeletons
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Most organisms lived in the seas—brachiopods and trilobites common
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Ancient continents lie south of the equator
Ordovician
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Warm shallow seas still cover much of the earth
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Ice cap covers what is now N. Africa
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First vertebrate (animal with a backbone) evolve, jawless fish were the first to evolve
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Silurian Period
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First land plants evolve and become abundant—grew low to the ground in damp areas
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Coral reefs develop
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Early continents collide with what is now North America, forming mountains
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Early fishes are common
Devonian Period-Age of the fishes
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Seas rise and fall over what is now North America
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Plants evolve to grow in drier areas—ferns were common plant type.
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Every main group of fishes were present in the oceans during this time
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Jaws, bony skeletons, and scales, sharks appeared during this time
Vertebrates reach land during this time- Lungfish and amphibians reach land
Carboniferous—
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Early Appalachian mountains form
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North America and northern Europe lie in warm tropical region
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Reptiles and giant insects (dragonflies and cockroaches) evolve
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Giant ferns and cone bearing plants formed vast swampy forests called coal forests
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Permian
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Desserts become larger in tropical regions
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Supercontinent Pangaea forms as all continents join together
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Reptiles evolve in many forms
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Period end with MASS EXTINCTION that kills most species of life
• Maybe asteroid
• Volcanic eruptions produced large amounts of CO2 and SO2 in the atmosphere
• Temperatures rose
• CO2 in oceans increased and amount of oxygen declined
• Scientists aren't sure why these things happened but believe all contributed to mass
extinction
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Mesozoic Era—AGE OF REPTILES
Triassic
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Pangaea holds together
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Hot dry conditions dominate center of Pangaea
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Fishes, insects, reptiles and conifers (plants that produce cones) survive the Permian extinction
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Reptiles flourish including the first dinosaurs
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Small mammals appear (mouse)
Jurassic
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Pangaea breaks apart as North America separates from Africa and South America
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Dinosaurs become common on land in the ocean and in the air.
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First birds evolve
Cretaceous
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Continents move toward their present-day positions as South America splits from Africa
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Dinosaurs are still widespread.
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Birds begin to replace flying reptiles—hollow bones make them better adapted for flying, flying reptiles become extinct
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First flowering plants appear
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Period end with MASS EXTINCTION that kills most species of life
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Asteroid hit earth—sent large amounts of dust and water vapor into the air that blocked the sunlight for years. Plants died, pla nt eating
animals starved
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Climate change caused by volcanic activity is also thought to have played a part in this mass extinction
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Cenozoic
Paleogene
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Australia becomes a separate continent
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Heavy volcanic activity occurs in the Pacific and Atlantic Oceans
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Mammals flourish
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Grasses first spread widely
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Climate warm and mild
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Mammals and dolphins evolve in the ocean
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Flowering plants, insects and mammals flourished on land
Neogene
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Climates change frequently, generally becoming drier
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Grasslands spread.
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The Andes and Himalayans form
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North and south America are connected.
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Some mammals become very large as do some birds
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Climate warm and mild
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Mammals and dolphins evolve in the ocean
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Flowering plants, insects and mammals flourished on land
Quaternary
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Thick glaciers advance and retreat over much of North America and Europe, parts of South America and Asia and all of Antarcti ca
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Many kinds of animals thrive. First modern humans evolve
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Climate cooled and warmed in cycles causing a series of ice ages
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Warm period began between 10,000 and 20,000 years ago
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In oceans coral, algae, mollusks, fish and mammals thrived.
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Flowering plants and mammals such as bats, cats, dogs and humans became common.