Measuring+absolute+time

Measuring absolute Time Tree rings- Each ring represents a single year (spring/fall) the width of the ring depends upon the temperature and rainfall. Varves- Glacial lakes deposits. A thick Light colored layer in the summer and a thin dark layer in the winter. Radioactive Dating used to date far back in time.Certain rocks contain radioactive isotopes Radioactive isotopes are atoms of elements that give off radiation from their nuclei Radioactive decay is the process by which a radioactive isotope changes into a new stable element. Half-life The rate at which a radioactive element decays. It is the time it takes for half of the atoms of the radioactive element to decay to a stable end product ( see page 1 of the ESRT) At the end of each half-life of the radioactive material remains Parent isotope= The Radioactive isotope that begins Daughter isotope- the stable isotope that has been changed. Radiocarbon Dating- Uses the radioactive isotope carbon-14 found in all living things. Because carbon-14 is continually absorbed by food an water it stays constant in living things. When the the living thing dies the percentage of carbon-14 decreases at the rate of its half-life. Can be used to date back about 100,000 years. Uranium lead method is useful to date rocks older than 10 million years. Can be used only on igneous rocks that contain the right kind of uranium. Rubidium-Strontium Method-Can also be used to date older rocks because of its long half-life. its also very commonly found in igneous rocks. Potassium-argon Method- Is very is useful since potassium 40 can be found in metamorphic, Sedimentary, and igneous rocks.It can be can older rocks but may also date rocks. It can date older rocks but way also dare rocks as young as 50,000 years