Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Download Science 8: Unit E – Topic 8 Notes: Fossils
Transcript
- - Science 7: Unit E – Topic 9 Notes: Geological History The history of the Earth from start to finish is divided into separate periods called _________. These eras can be millions, even billions of years old and they are not all the same length of time. One era ends and another begins usually when there is a _____ ________________ of life-forms such as when the dinosaurs died out after the meteor hit. Usually when this happens, a new class of organisms (living things) becomes ___________ on Earth. - The order of eras is ___________________________________ ________________________________________________________ - Because one era can be hundreds of millions years long each era is divided into __________. See p. 430. How to Determine the Ages of Rocks and Fossils I. __________ ________ – is the dating of rocks by comparing them to other rocks or fossils of well known organisms. There are two methods of relative dating. 1. ___________ ___ __________ – In an undisturbed sedimentary rock formation we know that the lower down the strata/layer of rock is, the older it is. 2. ________ _________ – If geologists find a fossil of a well known organism such as a fossil we can assume that the rock layer is as old the fossil that’s in it. For example we know that trilobites lived in the early Mesozoic Era and therefore if we find a rock containing trilobite fossils, then the rock itself is from that era as well. II. _________ ________ – is the dating of rocks and fossils using the radioactive properties of certain elements (uranium and the carbon-14 isotope). ___________ basically means that over time, certain materials such as uranium will change into another material. By studying the amount of the original material that is left, we can calculate the age of the rock. There are two methods of absolute dating: ____________________________________________ 1. ___________ ________ – The study of the amount of _________ _____________ compared to amount of _____________________ contained in a sample of rock. The lower the percentage of uranium, the older the rock is. The half-life of uranium is _____________, the same age as the Earth. No rock should therefore have a percentage of uranium of less than 50% compared to lead and few if any rocks have a percentage near 50% (because rocks that old have been recycled by the Rock Cycle). 2. ________________ – The study of the amount of _________ (parent material) compared to the amount of __________ (daughter material) contained in a fossil sample. The lower the percentage of Carbon-14, the older the fossil. This technique only works with fossils of less than __________ years. The half life of Carbon-14 is ______ meaning that half of the carbon-14 will turn into nitrogen over that time.
