Earth's History

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.…