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

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!

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

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