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Interpreting Geologic History. What happened when. Two types of dating:. Absolute Dating: Gives the exact age of a rock or a geologic event Ex. He was born on June 26 th , 1902 Dinosaurs went extinct 65.95 million years ago (true) - PowerPoint PPT Presentation
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Interpreting Geologic History
What happened when
Two types of dating: Absolute Dating: Gives the exact age of a rock
or a geologic event Ex. He was born on June 26th, 1902 Dinosaurs went extinct 65.95 million years ago
(true)
Relative Dating: Tells you the order in which rocks were created or geologic events took place Ex. He was the 2nd of 4 children The dinosaurs went extinct after the trilobites but
before the wholly mammoths.
Absolute Dating: Tree rings
Tree Rings: Every year trees leave a ring in it’s trunk. These vary on size based on the climate that year. Scientists can put together tree rings from ancient trees in an unbroken line all the way to the present.
Used very often in archaeology for dating wood beams and carvings.
Technical name is dendochronology
Absolute Dating: Index fossils
Scientists can know the absolute age of rock if they are able to find certain fossils in that rock called INDEX FOSSILS
These fossils are known to have lived only during a certain period of Earth’s history, were widespread, and died out or evolved suddenly
Examples are certain kinds of shells or trilobites.
Absolute Dating:Radioactive Dating
The most reliable method of absolute dating is RADIOACTIVE DATING.
When Magma cools to form an igneous rock it begins to emit radioactive particles at a constant rate. Scientists can measure how much radioactive material is left in a sample to determine when that rock first cooled from Magma. This works accurately for rocks up to 50 billion years old (far older than the age of the Earth or even the Universe)
Relative Dating Relative Dating tells scientists the order of
geologic events and rock formations. They use FOUR PRINCIPLES to guide their
analysis. We are going to discover these principles on
our own.
Create a 3 Color Stack of “Sedimentary Rock”
The Law of Superposition
In a sequence of undisturbed rock:
THE OLDEST ROCKS WILL BE AT THE BOTTOM
Now, Bend or Break your rock
FLOWUse “great pressure” to bend your rocks to make FOLDS.
FRACTUREUse “great pressure” (or string) to make a FAULT
The Law of OriginalHorizontality
Rocks are almost always laid down in flat horizontal layers.
If they are found so that they are bent or otherwise not horizontal, THE FORCE THAT BENT OR BROKE THEM MUST HAVE COME AFTER they were originally laid down.
Next, use a pencil to dig a hole into your
rock and fill it up with Igneous rock.
The Law of Cross Cutting Relationships An igneous rock that INTRUDES across other rock layers
is YOUNGER than the layers it cuts across.
UnconformitiesWhat is an unconformity?
An unconformity is AN UNDERGROUND ERODED SURFACE
Unconformities tell geologists that there was erosion and new layers started building on top
Unconformities obey the Law of Cross Cutting Relationships
An unconformity and everything above it are ALWAYS YOUNGER than what they cross-cut.
More Unconformi
ties
http://www.classzone.com/books/earth_science/terc/content/visualizations/es2902/es2902page01.cfm?chapter_no=visualization
Finally, split your rock almost into 2 and separate the sides to make a
“valley”
The Law of Lateral Continuity
Layers of rock extend in all directions and are the same even if separated by a valley or fault
On the other hand, rocks above or below may be very different. THERE IS MORE VARIATION BETWEEN ROCK TYPES UP AND DOWN THAN THERE IS SIDE TO SIDE
Let’s try some puzzles…
This one has Metamorphosis!
Tricky…
A little harder…
Uber-difficult (extra credit)
The technical name: Stratigraphy
Strata: Layers
Graphy: Study
Stratigraphy: Study of layers
Used in geology, paleontology, and archaeology to infer RELATIVE AGE of artifacts, bones, or rocks.
Archaeologist What do they do?
Excavate ruins of ancient cultures systematically and scientifically
Work for developers and construction companies that are required by law to check for artifacts before building
Forensic archaeologists work for the police to solve “cold cases”
Excavation can be grueling, slow and tedious. However, archaeologists can find incredible things and make amazing discoveries.
How do you become one?
To become an archaeologist you need to receive a bachelors degree in geology, anthropology, history, or archeology (if offered).
Almost all archaeologists have a Masters, or even a PhD.
Many college students work on archaeological digs during the summer in places all around the world.
Archaeology is a hard career to find a job in, perseverance is definitely required. They are paid between $37,000-55,000.