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ABSOLUTE AGE Absolute dating- used to determine the age of a rock or fossil more exactly based on the properties of atoms An atom:

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**In an atom, protons ( + ) and neutrons (neutral)**

are found in the nucleus. Electrons ( - ) are found in orbitals around the nucleus. Every element has an exact number of protons, neutrons and electrons in order to be stable.

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**An isotope is the same element with a different**

number of neutrons. Atomic mass - number of protons and neutrons combined Radioactive decay - the number of protons in an atom is changed; forms a new element Ex. - If parent material is Uranium (atomic mass 238), And the daughter material is lead ( atomic mass 206); caused by a loss of 32 protons after a long series of decay (Lead is not radioactive and will not decay any further.)

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**Each radioactive parent material has a certain rate at which it**

decays to its daughter material. Half-life -the time it takes for half of the atoms of the isotope to decay. Ex.- half -life of Carbon 14 is 5730 years, so it will take 5730 years for half of the C-14 in an object to become nitrogen-14

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**The Half-life of Bismuth**

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**How can knowing the half-life of Carbon-14 help scientists**

find out the age of a fossil? Radiometric dating - measure amounts of parent/daughter materials; if know half-life of material and original amount, Can calculate absolute age Carbon-14 is useful for dating rocks and fossils up to 75,000 years old. Uranium 238 is used for older objects. Based on radiometric dating, the age of the earth is estimated to be 4.6 billion years.

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**Try this example problem:**

An object is found to contain 2 grams of C-14. A similar bone (from today) is found to contain 4 g of C-14. Approximately how old is the bone?

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History of Life: Origins of Life Chapter 14-3. Age of Earth The earth is about 4.5 billion years old How did we measure that? Radiometric Dating = calculating.

History of Life: Origins of Life Chapter 14-3. Age of Earth The earth is about 4.5 billion years old How did we measure that? Radiometric Dating = calculating.

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