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RELATIVE VS. ABSOLUTE DATING

FORCES THAT CHANGE THE EARTH

UNIFORMITARIANISM VS. CATASTROPHISM

CATASTROPHISM

UNIFORMATARIANISM

The same geologic processes that are happening today are the same processes that have been shaping the Earth throughout its history.

  • Weathering
  • Erosion
  • The principle that states that all geologic change occurs suddenly.
  • Earthquakes
  • Floods
  • Volcanic activity

This principle was stated by James Hutton about 250 years ago

Before Uniformatarianism, this was the principle that most scientists believed.

A HAPPY MEDIUM

Today, scientists believe that both principles affect our Earth. Although most geological processes occur slowly, Earth does experience sudden geologic events.

ABSOLUTE DATING

RELATIVE DATING

A method of determining whether an event or object is younger or older than another event or object.

Measuring the age of an event or object in years.

RELATIVE DATING ABSOLUTE DATING

RADIOMETRIC DATING

THE PRINCIPLE OF SUPERPOSITION

  • Finding the age of an object.
  • More specific

Younger rocks lie above older rocks in undisturbed sequences.

Method of finding out the age of an object by figuring out the ratio of parent material to daughter material.

Okay, don't worry. I am going to explain this.

  • Finding out whether an object is older or

younger than another object.

  • Not specific or exact.

LET ME TELL YOU A STORY. THIS IS A STORY ABOUT MR. & MRS. ISOTOPE AND THIER DAUGHTERS. CLICK ON THE VIDEO BELOW TO LEARN MORE ABOUT THIS VERY UNSTABLE FAMILY.

DISTURBANCES IN ROCK LAYERS

RADIOACTIVE DECAY

To determine absolute age, scientists look at the breaking down of an unstable isotope into a stable isotope.

Unconformities are missing rock layers. Usually due to erosion.

Not all rock layers are in nice and neat straight rows. Many have features that cut through them. The principle of crosscutting relations states that geologic features such as faults and intrusions are younger than the rock they cut through.

HALF LIFE

The amount of time it takes for half of the radioactive sample to decay. In other words, the amount of time it takes for half the parent material to decay.

After watching the video on the next screen, I think you will have a better understanding.

ISOTOPES

An atom that has a different number of neutrons than other atoms of the same element.

Most isotopes are stable, but some are unstable. We call them radioactive. These isotopes break down, trying to become stable. This is called radioactive decay. The rate of decay is constant.

The unstable isotope is called the parent isotope. The stable isotope that is produced is the daughter isotope.

FAULT

INTRUSION

EXAMPLE:

  • Absolute Dating
  • I have been teaching at EMS for 6 years. This is exact.
  • Relative Dating

I started teaching at EMS after my daughter Alex was born. She is 8 years old. This is relative. You only know that I have worked there less than 8 years.

THE GEOLOGIC COLUMN

DISCONFORMITY

When a rock layer is missing.

Due to:

  • Uplifting
  • Erosion

At some future time deposition begins again.

NONCONFORMITY

Where sedimentary rock layers lie on top of an eroded surface of nonlayered igneous or metamorphic.

Watch the following video. It is an excellent example of unconformities and the 3 main categories.

  • Disconformity
  • Nonconformity
  • Angular Unconformity

Like I said before not all rock layers are in nice neat rows. Because of disturbing forces, the disruption in the rock layer sequence can be a challenge for geologists.

ANGULAR UNCONFORMITY

Exists between horizontal rock layers and rock layers that are tilted or folded.

Geologists combine data from all know undisturbed rock sequences from around the world to create an ideal sequence of rock called the GEOLOGIC COLUMN.

Click on the link below to view "What is Relative Dating?"

NOW LET'S PRACTICE FIGURING OUT WHICH LAYERS ARE THE YOUNGEST AND OLDEST. ON A PIECE OF PAPER, PUT THE LAYERS IN ORDER FROM OLDEST TO YOUNGEST.

http://education-portal.com/academy/lesson/what-is-relative-dating-law-of-superposition-principles-of-original-horizontality-cross-cutting-relationships.html

The answers will be on the next section.

Picture #2

Oldest to youngest

C

B

A

D

E

Picture # 1

Oldest to youngest

B

C

D

A

E

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