Absolute Time

Historical Methods Erosion and Sedimentation  Scientists estimate the amount of time it would take for the needed erosion or sedimentation to occur  Only effective for young geologic features

Tree Rings  One Ring forms each year  Spring Wood (growing season)  Summer Wood (dry season) Ring thickness depends on temperature and rainfall Ring Patterns can be correlated from tree to tree  Can be used to determine the dates of construction for different artifacts

Varves A sediment that is deposited on a yearly cycle  In any large body of water Clearest in glacial lakes  Summer and Winter lake levels will differ  Glaciers As ice retreats (melts) in the summer and accumulates in the winter it will leave a varve as well

Radiometric Dating Atoms with the same number of protons but different numbers of neutrons are called isotopes.  Heavy isotopes (those with more neutrons) are unstable and emit radiation. The original atom is called the parent The new atom is called the daughter  e.g.

Half-Life: The amount of time it takes for half the radioactive atoms in a sample to decay to a stable product  The proportions of parent isotopes vs. daughter isotopes in a sample can be used to date that sample

Example: Carbon-14 has a half-life of 5730 years. If I extract all of the Carbon-14 and Nitrogen-14 out of a leaf and I find that what I have is only ½ Carbon- 14, how old is my leaf? ¼ Carbon-14, ¾ Nitrogen-14?

Parent isotope Daughter isotope Half-Life (yrs.)Effective Range (yrs.) Material to Date Carbon-14Nitrogen ,000Once living things Uranium- 238 Lead billion>10 millionIgneous Oldest rocks Rubidium- 87 Strontium-8747 billion>10 millionIgneous/ Metamorphic Oldest rocks Potassium- 40 Argon billion>50,000Igneous Rocks

Types of Decay Alpha Decay:  When the parent isotope emits a Helium atom along with the daughter isotope. 238 U 4 He Pb  Circle the alpha particle  Put a box around the parent isotope  Underline the daughter isotope

Beta Decay  When the parent isotope emits an electron along with the daughter isotope. 14 C e N  Circle the beta particle  Put a box around the parent isotope  Underline the daughter isotope

Why is radiometric dating so important? Because it can be verified by different methods it has proven to be very accurate This helps scientists to put absolute dates on events that have happened in the past

What was a historical method of absolute dating? 1. Erosion 2. Sedimentation 3. Tree Rings 4. Varve 5. All Of The Above

Why is radiometric dating important? 1. It allows us to accurately measure how much glacier melt there is 2. It allows us to measure the ages of things accurately even if they are really old 3. It allows is to see how many electrons there are in atoms

Radioactive element X has a half- life of 1000 years. How old is something if only 25% of it is left? years years years years years

What is alpha decay? 1. When the parent isotope emits an electron along with the daughter isotope. 2. When an atom fuses together 3. When an atom gains an electron 4. When the parent isotope emits a Helium atom along with the daughter isotope.

What is beta decay? 1. When the parent isotope emits an electron along with the daughter isotope. 2. When an atom fuses together 3. When an atom gains an electron 4. When the parent isotope emits a Helium atom along with the daughter isotope.

What is electron capture? 1. When the parent isotope emits an electron along with the daughter isotope. 2. When an atom fuses together 3. When an atom gains an electron 4. When the parent isotope emits a Helium atom along with the daughter isotope.