Thursday December 2, 2010 (Radioactivity and Radiometric Dating; Project - Fossils)

ThursdayDecember 2, 2010

(Radioactivity and Radiometric Dating;

Project - Fossils)

The Launch PadThursday, 12/2/10

List four examples of indirect fossil evidence.

Tracks

Burrows

CoprolitesGastroliths


The Principle of Fossil Succession states that:

fossils succeed one another in a

definite and determinable

order.


Index fossils work on the premise that:

although different sediments may look different depending on the conditions under

which they were laid down, they may include the remains of the same species of

fossil.

AnnouncementsWe will have a test next

Wednesday.

Assignment Currently Open Pages Date of Notes

on Website Date Issued Date Due

Five Multiple Choice

Questions on Plate Tectonics

11/11 11/12

Project – Decade

Volcanoes11/15 11/19

Project – Killer Earthquakes

11/17 12/1

Project – Greatest

Mountains11/19 12/3

Radioactivity and Radiometric Dating A Quick Review of Atomic

Structure There are two main regions of an atom:

the nucleus, containing positively-charged protons

and neutral neutrons. the electron cloud,

containing negatively-charged electrons orbiting

the nucleus.

A Quick Review of Atomic Structure

An element’s identifying number is its atomic number, the number of protons in the atom’s nucleus

An element's mass numberis the number of protons plus

(added to) the number of neutrons in the atom’s nucleus.Isotopes are atoms of the same

element that have different numbers of neutrons and therefore different mass

numbers.

Radioactivity and Radiometric Dating

Radioactivity Radioactivity refers to the particles and energy which

are emitted from nuclei as a result of nuclear instability.


Because the nucleus experiences the intense conflict between the two strongest forces in nature

(electromagnetism and the strong nuclear force), it should not be surprising that there are many nuclear

isotopes which are unstable and emit some kind of radiation.

Radioactive Decay Radioactive decay is the spontaneous

disintegration of a nucleus into a slightly lighter nucleus, accompanied by emission of particles,

electromagnetic radiation, or both.

The most common types of radioactive decay are alpha, beta, and gamma radiation.


Types of Radioactive Decay Alpha emission results in the release of an alpha particle, which consists of two protons and two neutrons bound

together.Alpha particles are helium nuclei and have a charge of 2+.


Types of Radioactive Decay Beta emission occurs when an elements

are unstable because they have too many neutrons.

To decrease the number of neutrons, a neutron can be converted into a proton

and an electron.The electron is emitted from the nucleus

as a beta particle.A beta particle is an electron emitted

from the nucleus during some kinds of radioactive decay.


Types of Radioactive Decay Gamma emission occurs when gamma rays, (highest-energy

electromagnetic waves) are emitted from a nucleus as it changes from an excited state to a ground energy state.


Parent and Daughter IsotopesAn unstable (radioactive) isotope of an

element is called the parent. The isotopes resulting from the decay of the parent are called the daughter isotopes

(or products.)


parent

daughter

Radiometric Dating

Half-life is the time required for half of

the atoms of a radioactive sample

to decay.This technique yields

numerical data for the age of rocks and

fossils.



Carbon-14 Dating Carbon-14 is the radioactive isotope of carbon. C-14 is constantly produced in Earth’s upper atmosphere as a

consequence of cosmic ray bombardment. Cosmic rays are high-energy particles that shatter the nuclei of gas atoms,

releasing neutrons. Some of the neutrons are absorbed by nitrogen atoms, causing their nuclei to emit a proton. As a result, the atomic number decreases by one (7 – 6), and a

different element, carbon-14, is created.This isotope of carbon quickly becomes incorporated into carbon dioxide, which circulates in the atmosphere and is absorbed by living matter. As a result, all living organisms

contain a small amount of C-14, including you!


Figure 11.18

Carbon-14 Dating While an organism is alive, the decaying C-14 is constantly

replaced, and the proportions of C-14 and C-12 remain constant. C-12 is the stable and most common isotope of carbon.

However, when any plant or animal dies, the amount of C-14 gradually decreases as it decays to nitrogen-14 by beta emission.

By comparing the proportions of C-14 to C-12 in a sample, the age of the sample can be determined.

Carbon -14 has a half-life of only 5,730 years, so it can only be used to date relatively recent events.

C-14 dating has become a useful tool for paleontologists, anthropologists, archaeologists, historians, and geologists who

study very recent Earth history.


Dating Sedimentary Strata Using Radiometric Dating

Figure 11.21

Project - FossilsYour presentation on fossils should

include the following:

Definition of “fossil”, definition of “paleontology”, the eight general types of

fossils, the fours types of indirect fossil evidence, the conditions that favor fossil preservation, summary of the Principle of

Fossil Succession, and definition of the term “index fossil”, and how they’re used.

NOTE: All topics must be illustrated!

You can do this on a sheet of paper, or electronically using Open Office Impress (send this to my e-mail).

Documents

Thursday December 2, 2010 (Radioactivity and Radiometric Dating; Project - Fossils)