Earth’s Layered Structure
Unravel Earth’s Her-story •Age Relationships Among Rocks •Relative Dating •Gaps in the Rock Record •Fossil Clues •Absolute Dating
Age Relationships Among Rocks How do we tell geologic time?
Law of Superposition “Sedimentary layers are deposited in a time sequence, with the oldest on the bottom and the youngest on the top.” Youngest
Avicenna
Oldest
Nicolas Steno
Fossil Correlation
Uses fossils to identify, reconstruct, and match complex or widely separated beds William Smith in sedimentary sequence
Crosscutting Relationship A rock or fault is younger than any rock/fault through which it cuts
James Hutton
Uniformitarianism
"The Present is the Key to the Past"
I’m Ana Marie, and I’m 16.
I’m Ana Rose, and I’m 16, too. We just had our birthday.
Goo-goo, ga ga. glur gooagu!
Yo, it’s Nick. What’s up!?
It’s me, Didi, a happy 13 yr old girl.
I’m 10 years old, dude.
I’m turning 17 this summer.
Hey guys, want to play baseball?
Ronald
Relative Dating Places events in their proper sequence or order
Geologic Column
Gaps in the Rock Record
Unconformities • Surfaces that separate a series of rock layers
TYPES
Angular Disconformity Nonconformity Unconformity
Disconformity 1
Sea level drops and erosion occurs 2
Sedimentary Beds
Sea level rises
New sediments
3
4
Nonconformity Rock cools and uplifted Erosion occurs Sea level rises and sediments accumulate
Angular Unconformity 1 2
Folding and uplift
Erosion occurs
Sea level rises and sediments deposited
3
4
Geologic History Beds Beds
Granite
Folded Beds
Pluton Basalt Dike
Gneiss and Schist (basement)
Fossil Clues
Fossil Clues
Types of Fossil Preservation
a. Petrified b. Mold & Cast c. Carbon Impressions d. Resin Fossils
Extinction Fossilized leg of a dinosaur.
Index Fossils
Ammonoids Ammonites
Ceratites
Goniatites
Facies fossils
Absolute Dating • A method that determines the actual length of time between events.
Radiometric Dating • Method of using the decay of radioactive elements to determine the absolute age of rocks • Half-life – the amount of time needed for one-half of the atoms of an element to decay • Daughter elements – new elements formed during the decay
Radiometric Dating • Radiocarbon dating – wherein the approximate time an organism died is found by comparing the amount of carbon-14 in the fossil remains with the amount of carbon-14 in the same amount of living matter.
Radiocarbon dating
The possession of knowledge does not kill the sense of wonder and mystery. There is always more mystery.…