geologic time when time rocks…. get it?!!. geologic time geologic time: is the study and...
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Geologic TimeWhen time rocks….
Get It?!!
Geologic Time
• Geologic Time:• Is the study and interpretation of Earth’s past. • By looking at a cross-section of land, or an
outcrop, we can gain evidence about how it formed.
• It is like solving a puzzle
If It’s a Puzzle, We Need….
• The puzzle pieces.• Two types of ages:• Relative Dating: when we compare the age of
a rock or event to another rock or event in a geologic sequence (no numerical age, just a round about age)
• Absolute Dating: the actual, numerical age, of a rock or event.
• We are going to begin with relative aging.
1.) The Principle of Uniformiatrianism
• WHAT!!!!!!• Uniform: • The same• -trianism:• Processes
• “the present is the key to the past”• All of the geologic processes that shape the Earth
today are the same ones that shaped the Earth in the past.
• This rule always starts us out.
Geologic Processes• Early Earth:• Volcanism• Pangea:• Tectonic Plate Movement• Formation of Landscapes:• Weathering and Erosion
• All of these were found in rock records from the past and the present.
• So we can assume it will occur in the future as well.
2.) The Principle of Original Horizontality
• Sediments are deposited in horizontal layers that are parallel to the surface on which they were deposited.
• If layers are not completely horizontal, an unconformity (erosion)must have come after the layer was created.
• This is usually our second piece of evidence in most landscapes.
3.) The Principle of Superposition
• In a series of undisturbed layers, the oldest layer is on the bottom and each layer on top of that gets progressively younger.
• This does not apply in cases where layers have been overturned or where older rocks have been forced over younger layers along a fault.
Folding and Faulting
• These mess up the principle of superposition.
Index Fossils
• Index Fossils:• Fossils that can help us determine the relative
age of a layer.• They are distributed over a large geographic
area but for a short amount of time.• (horizontally not vertically)
Wide Spread Geographic Area
Time
Looking At Events
• 4.) Igneous Intrusion and Extrusions:• Igneous INtrusion:• when molten magma forces its way through
other layers is called an intrusion. • Contact Metamorphism shows this.• Igneous EXTrusion:• When lava solidifies at Earth’s surface, it forms
a mass of igneous rock called an extrusion.
Rules
1. PU2. POOH3. PSP4. U/E5. F/F6. Ig (int/ext)7. CCR
EVENTS
Radioactive Decay• Radioactive Decay:• Occurs when unstable atoms break down
(decay) into radioactive elements (decay product).
• Atoms with the same number of protons but a different number of neutrons are called isotopes.
C6 protons
6 neutrons
12
8 neutrons
6 protons
C14
Radioactive isotopeStable
atom
Half-LifeHalf-life is the amount of time it takes for the original product to disintegrate (break down) by half into the decay product
CARBON-14 is used for fossils b/c of its short half-life
Number of Half-Life
Years Orig. % Decay % Orig. GramsLeft
Pie Chart