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SOL ES9 Paleontology Absolute Dating What is Absolute Age? • Absolute Age is determining the exact age of an object or event. • Note that NUMBERS MUST BE ASSIGNED TO THE OBJECT OR EVENT What is radioactive decay? • Rocks can often contain radioactive isotopes – radioactive isotopes emit particles and energy at a constant rate – atoms change from one type to another until they become stable – provides accurate method for finding the exact age of a rock • Scientists measure and compare the ratios of radioactive and stable isotopes to determine absolute age. – radioactive = parent material – stable = daughter material What is a half-Life? • The rate of radioactive decay is constant and predictable for each element – not affected by temperature, pressure, or other environmental factors • Scientists must know the half-life of an element to calculate age – Half-life: is the amount of time required for ½ of radioactive material to decay into stable material. • note: ALWAYS take ½ of the radioactive material What is radiometric dating? • Radiometric Dating is the process of comparing the amount of parent material to daughter material to determine age • Any daughter material found in a sample had to form after the sample solidified. • As time passes, the amount of daughter material increases and the amount of parent material decreases at a predictable rate. What is the uranium – lead method? • Uranium-238 (U-238) will decay into Lead-206 (Pb-206) • Half life = 4.5 billion years • Used for rock samples over 10 million years old What is the potassium – argon method? • Potassium-40 (K-40) will decay into Argon (Ar) and Calcium (Ca) • Half life = 1.3 billion years • Used for rock samples between 50,000 and 4.6 billion years old What is the carbon 14 method? • Carbon exists in two forms: – carbon-14 (radioactive) – carbon-12 (stable) • Both occur in the atmosphere combined with oxygen to form carbon dioxide – most CO2 is made with carbon-12 – living plants take in CO2 during photosynthesis and the carbon moves through the food chain • Half life = 5,734 years • Used for ORGANIC samples less than 70,000 years old