ABSOLUTE DATING

ELEMENT- Made-up of one type of atom. One element may have several forms. ISOTOPES- A form of an element with more or fewer neutrons than other forms of the same element. EXAMPLE: N P CARBON-12 ATOM CARBON-14 (NORMAL) (ISOTOPE)

Absolute Dating Radioactive Elements Decay at a specific rate They break down into other elements The rate is unaffected by environmental factors RADIOACTIVE DECAY ELECTROMAGNETIC ENERGY N P CARBON-14 ATOM (RADIOACTIVE) NITROGEN-14 (STABLE)

HALF-LIFE- The time it takes one half of the atoms in a given sample of radioactive isotope to decay Each radioactive isotopes has it’s own half-life. The half-life can not be changed. It is unaffected by external factors like temperature or pressure.

RADIOACTIVE MATERIAL DECAY PRODUCT FIRST HALF LIFE 1 1/2 At the end of one half-life, half the original atoms will have decayed, and half will have remained unchanged.

SECOND HALF LIFE 1/2 1/4 At the end of the second half-life, half of the remaining atoms decay, and a quarter of the original atoms unchanged.

This "halving" goes on indefinitely. THIRD HALF LIFE 1/8 1/4 At the end of the third half-life, half of the remaining quarter is decayed, leaving one-eighth of the original atoms unchanged. This "halving" goes on indefinitely.

Half-Life

ABSOLUTE (RADIOACTIVE) DATING Age of a rock can be determined by comparing the amount of undecayed substance to the amount of decayed substance. Since Carbon-14 has a relative short half-life it is good for dating rock with ORGANIC remains that are only 50,000 years old (or less). Other radioactive isotopes that have longer half-lives (Uranium-238) are useful in dating older rocks, millions or billions of years.

Radioactive Decay

Carbon-14 Dating Half-life is about 5,700 years Good for organic remains Good for things that are not too old (<50,000 years old)

100% Carbon 14 50% Carbon 14 50% Nitrogen 14 50% Carbon 14 FIRST HALF LIFE 100% Carbon 14 50% Carbon 14 50% Nitrogen 14 (5,700 yr) SECOND HALF LIFE 50% Carbon 14 50% Nitrogen 14 (11,400 yr) 25% Carbon 14 75% Nitrogen 14 THIRD HALF LIFE (17,100 yr) 25% Carbon 14 75% Nitrogen 14 12.5% Carbon 14 87.5% Nitrogen 14

GEOLOGIC TIME SCALE: A model of the geologic history of the Earth and the geologic events that have taken place over the 4.6 billion years of Earth’s existence. It is mainly based on rock and fossil evidence. The divisions are: 1. EONs (largest) 2. ERAs 3. PERIODs 4. EPOCHs (smallest)

***See Earth Science Reference Tables***

Evolution of Life on Earth Fossil Evidence Very few organisms ever become fossils The fossils we have show a change in life forms over time – organic evolution There were several mass extinctions in the past The last one was 65 million years ago This signaled the end of the dinosaurs Mammals became the dominant life form on land Comet or asteroid collisions may be linked to the mass extinctions