absolute age: identifies actual age of a rock layer if actual time of two events is known, the length of time between two events can be calculated

(1) rates of erosion and deposition example: Niagara Falls

(2) counting tree rings

(3) varve count: method for establishing age of certain sediment deposits shows a yearly cycle- layers of light/dark bands can form in any body of water; clearest in glacial ice

(4) radioactive elements elements that emit particles and energy while forming new isotopes or elements each time a particle is released, the atom changes to a new, lighter element in process of radioactive decay

radioactive decay is not affected by changes in temperature, pressure, or environmental changes

half-life: the time it takes for half of the atoms of a radioactive element to decay ranges from a second to billions of years

carbon dating: an isotope of carbon used in radioactive dating half life of carbon is 5,300 years uses Carbon-14 two problems: (1) cannot use on rocks, only things once alive (2) half-life for carbon is short