Geologic Time 10/29 – 10/31

Bell Ringer Monday 10/29/2012 ● What types of things do you think might mark the end of a geologic era?

Era-Ending Events ● Natural disaster (e.g. meteor) ● Climate change (e.g. ice age) ● Mass extinction and rise of new predominant animal species

Fossil Evidence for Change ● Fossils represent remains of once-living organisms, many of which are now extinct. ● Kinds of fossils found in rocks of different ages differ because life on Earth has changed over time.

Classwork ● You will be completing “Who's On First?” procedure B. Please begin by reviewing the handout on the Law of Superposition.

Bell Ringer Tuesday 10/30/2012 ● What facts do you know about this animal? Come up with as many as you can think of. Try to think of both physical characteristics and behaviors.

Brainstorming... Properties of a Horse

Follow-up... ● What would you know about this animal if it was extinct and you only had fossil evidence to learn about it?

Fossil Evidence: Stegosaurus ● What do we know about fossilized animals like this one? What can you infer about it based on fossil evidence?

Classwork ● Read “Death of the Dinosaurs” article and answer comprehension questions on a separate sheet of paper.

Absolute Age Dating Outline: ● What is absolute age dating? ● What is radiometric dating? ● Review: what is an isotope? ● What is a radioactive isotope? ● What is half life? ● Why use Carbon-14?

What is absolute age dating? ● Absolute-age dating enables scientists to determine the actual age of a rock, fossil, or other object.

What is radiometric dating? ● Scientists attempt to determine the ratio of 'parent nuclei' to 'daughter nuclei' within a given sample of a rock or fossil. ● This ratio is then used to determine the absolute age of the rock or fossil.

Radiometric Dating ● Radiometric dating works because certain isotopes of atoms are radioactive, which means they decay into other kinds of elements. ● A specific element does this in a predictable time, called the half life, which is how scientists use the ratio of parent and daughter nuclei to determine age.

Review: what is an isotope? ● An isotope is an atom of a given element with a different number of neutrons but the same atomic number (which is the number of protons) ● For example, U-237 and U-238 are both uranium and have atomic number 92, but have different mass numbers (237 and 238) which means different numbers of protons.

What is a radioactive isotope? ● A radioactive isotope is an isotope of an element that decays and emits radioactive particles to become another type of element. ● For example, Carbon-14 decays into Nitrogen- 14

What is half-life? ● Half-life measures the amount of time it takes for half of a radioactive isotope sample to decay into its product. ● For example, Carbon-14 has a half-life of 5730 years. So if you start with 100 grams of Carbon-14, after 5730 years there will be 50 grams of Carbon-14 and 50 grams of Nitrogen- 14.

Why use Carbon-14? ● Carbon is especially useful for finding the age of materials that are of organic origin, such as amber, humanoid bones, papyrus, and charcoal fragments, because all organic materials contain carbon. ● Uranium is particularly useful for very old materials because its half-life is very long (700,000,000 years).

Carbon-14 Carbon-14 has atomic number 6 and atomic mass 14 ● How many protons? _____ ● How many neutrons? _____ ● How many electrons? _____

Exit Slip: Answer Questions & Turn In ● Why use carbon for dating? ● How did I figure out that 25% of the original amount of carbon in a sample is left after two half lives go by? ● What is the difference between relative and absolute age dating? ● HOMEWORK: BRING TEXTBOOK FRIDAY!