Relative vs. Absolute Dating Magazines can be piled up and you can know the relative age of the magazine by observing the order in which the magazines were stacked Absolute dating is a process that uses the properties of atoms in rocks and other materials to determine a more accurate age of rock layers

What are Atoms and Elements? Atoms are the particles or “building blocks” of which all matter is composed Atoms combine, like blocks snapping together, to form many different types of matter. Specific types of atoms are called elements (i.e. oxygen, carbon, gold, etc.) Some atoms “fall apart” or change over time

Three basic particles make up an atom Protons, Neutrons, and Electrons: In the nucleus: Protons: Particles that have a positive electrical charge Larger than neutrons Neutrons: Particles that have no electrical charge Smaller than protons The nucleus has a positive charge Around the Nucleus: Electrons: Negatively charged particles that move around the nucleus Smallest of particles There is one electron for each proton

Atom Diagram Nucleus (contains Protons & Neutrons) Electrons (move around the Nucleus)

Special Atoms: Isotopes If the amount of protons in an atom changes, a new element is formed e.g. Carbon has 6 protons; Nitrogen has 7 protons However, if the number of neutrons are changed, the type of element is not changed e.g. Carbon can continue to exist with different amounts of neutrons (Carbon-14 indicates the total of protons and neutrons. It still has 6 protons) Atoms of the same element that have an unusual number of neutrons are called isotopes Isotopes are unstable atoms e.g. Carbon-14 is an unstable Carbon atom or isotope

Unstable Isotopes break down In a process known as radioactive decay, One of the isotopes neutrons breaks down, changing into a proton and an electron Some isotopes give off two protons and two neutrons in the form of an alpha particle (see diagram-one after next slide) The electron leaves the atom as a beta particle (see diagram-one after next slide) The nucleus loses a neutron but gains a proton In the end, a new element is formed

Radioactive Decay Diagram Decay of: 2- neutrons 2-protons 1 2 3 Uranium-238 Lead-206 (eventually) Uranium-238 decays by emitting alpha particles (two protons and two neutrons) and beta particles (one electron). A beta particle is produced when a neutron decays and becomes a proton.

Similar Chart: Uranium-238 to Lead-206 The decaying process is complex but scientists believe the process follows a pattern You do not need to memorize or understand this chart

Radioactive Decay Example When atoms of the radioactive isotope uranium-238 decay, they eventually form atoms of lead-206 Lead-206 is not radioactive, so it will not decay any further In this example, uranium-238 is known as the parent material, and lead-206 is known as the daughter product

Radioactive decay is measured by the material’s “Half-Life” The half-life is the rate, or speed, at which the radioactive parent material decays into its daughter product The half-life is the total amount time it takes for half of the atoms in the material to decay Different isotopes decay at different rates “Whole-life” “Half-life”

Half-Life Example Parent material: Carbon-14 1st 5,730 yrs. Parent material: Carbon-14 It takes 5,730 years for half of the Carbon-14 material to decay into its daughter product Nitrogen-14 Then, it takes another 5,730 years for ½ of the remaining Carbon-14 material to decay Therefore, after 2 half lives, ¼ of the original carbon-14 atoms still remain And, after 3 half lives, 1/8 of the original carbon-14 atoms still remain Nitrogen-14 2nd 5,730 yrs. Carbon-14 Nitrogen-14 Nitrogen-14

Half-Life Sequence diagram Eventually, such a small amount of the parent material is left that it may not be measureable. Note: There is no time period identified in this example. Yet, the half-life, or period of decay, remains the same between each half-life

Radiometric Dating To a geologist, the decay of radioactive isotopes is like a clock ticking away, keeping track of time that’s passed since rocks have formed As time passes, the amount of parent material in a rock decreases as the amount of daughter product increases A geologist can calculate the absolute age of a rock by measuring: the amount of parent and daughter materials in a rock and knowing the half-life of the parent

Radiometric Dating is Absolute Dating…with Limitations Carbon-14 is useful for dating fossils, bones, and wood up to 50,000 years old Rock that can be radiometrically dated are mostly igneous and some recrystallized metamorphic rocks Only some sedimentary rock The amount of starting material can come into question Decay rates are assumed to be uniform over time Radiometric dating has been used to date the oldest rocks found on Earth (3.96 billion years old) Scientists have estimated the age of Earth at 4.6 billion years