1. Evolution
Theory that explains all of the changes that have happened to living organisms on earth
Based many experiments and much information
Some information/experiments are debatable, most are indisputable
Earth’s age:
About 4.5 billion years old
Estimate was based on the earth’s crust; now based on radioactive dating
Radioactive Dating:
Radioactive Isotopes are used (proton # the same, neutron # different)
Isotopes are unstable and decay at a steady rate that can be measured
Half Life – the time it takes for half of any sample to decay
Ex: 10 grams of an isotope; half-life is 5,000 years.
In 5000 years – 5 grams
10,000 years –2.5 grams
15,000 years – 1.25 grams

2. Evolution
Half lives vary from fractions of seconds to billions of years
14 C: half life of 5,730 years – used for newer objects
40 K: half life of 1.25 billion years – used for older objects
Early Evolution Scientists:
Lamarck (1800) – Stated that animals change over time by passing on acquired traits
If this were true… giraffes would stretch their necks to reach higher trees
- Giraffe necks get longer
- Offspring acquire the long neck
Not accepted anymore!

3. Evolution
Wallace (1840) – animals change by passing genetic traits that are best suited for the environment
Ex: Giraffes all have different neck sizes due to gene variations (short, medium, long alleles)
- During times of drought or a lack of low growing plants, long/medium necked giraffes survive, short-necked giraffes die.
- Longer-necked giraffes mate, have similar offspring

4. Evolution
Charles Darwin (1840) – same theory as Wallace, but Darwin published a book (Origin of Species by means of Nat. Selection)
Based on observations made as a naturalist on the H.M.S Beagle
Traveled the world collecting samples (Galapagos islands)
Wrote and thought about the following:
Living Diversity – Many species are almost identical
Fossil Diversity – 99.9% of all species are extinct
Adaptation – Inherited physical or behavioral trait to increase survival chances
Fitness – ability to stay alive and reproduce
Variation – inheritable differences in a trait