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

The Launch Pad Thursday, 12/2/10 List four examples of indirect fossil evidence. Tracks Burrows Coprolites Gastroliths

The Launch Pad Thursday, 12/2/10 The Principle of Fossil Succession states that: fossils succeed one another in a definite and determinable order.

The Launch Pad Thursday, 12/2/10 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.

Announcements We will have a test next Wednesday.

Assignment Currently Open Pages Date of Notes on Website Date IssuedDate Due Five Multiple Choice Questions on Plate Tectonics 11/1111/12 Project – Decade Volcanoes 11/1511/19 Project – Killer Earthquakes 11/1712/1 Project – Greatest Mountains 11/1912/3

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 number is 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. Radioactivity and Radiometric Dating 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. Radioactivity and Radiometric Dating

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 +. Radioactivity and Radiometric Dating

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. Radioactivity and Radiometric Dating

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. Radioactivity and Radiometric Dating

Parent and Daughter Isotopes An 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.) Radioactivity and Radiometric Dating 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. Radioactivity and Radiometric Dating

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! Radioactivity and Radiometric Dating

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. Radioactivity and Radiometric Dating

Dating Sedimentary Strata Using Radiometric Dating Figure 11.21

Your 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 ).