1. … it is highly important for us to gain some notion, however imperfect, of the lapse of years. Charles Darwin: On the Origin of Species 1859 Chapter 9: On the Imperfection of the Geological Record

2. Relative dating -The proper chronological placement of a feature, object, or happening in the geologic time scale without reference to its absolute age.

3. Absolute dating - used by geologists to determine the actual age of a material. It can be achieved through the use of historical records and through the analysis of biological and geological patterns. Some archaeologists prefer the terms chronometric or calendar dating, as use of the word "absolute" implies a certainty and precision that is rarely possible in archaeology.

4. Radiometric dating is based on the constant rate of decay of radioactive isotopes.radioactive isotopes Radioactive isotopes are atoms that have a bit too much weight on them (kind of like most Americans). Some of the most typically referenced ones are carbon-14 and uranium- 238.

5. If an atom is unstable (also known as (aka) radioactive), then the bit extra it is carrying is extra protons (or neutrons). As time passes, the extra protons/neutrons get lost until the element is changed into a new one. In the case of carbon-14 it becomes carbon-12. With uranium-238, though, it becomes lead- 206…a totally different element. Half-life is the time it takes for HALF of the element to change.

6. A geologic eon is the largest division of time in geology, and is generally considered to be around a billion years Eras – a very long span of geological time Periods - a unit of geological time during which a system of rocks formed Epochs – the shortest time division in geologic history

7. www.enchantedlearning.com Search for Geologic time scale