CHAPTER 14 NOTES HOW LIFE BEGAN?

Inorganic (nonliving) matter was transformed into simple organic molecules Miller-Urey experiment (they modeled the ancient atmosphere in a reacting chamber, then electrodes produced sparks to simulate lightning and after one week they found the liquid produced by the experiment contained amino acids – the building blocks of proteins) Eventually these simple organic molecules changed into cells with DNA and a nucleus

FOSSILS Paleontologists are scientists who study fossils The fossil record provides evidence about the history of life on Earth and it also shows how different groups of organisms, including species, have changed over time Most fossils form in sedimentary rock

FOSSIL DATING RELATIVE VS. RADIOACTIVE

RELATIVE DATING Determines the age of a fossil by comparing its placement with that of fossils in other layers of rock Oldest fossils are in lower layers of the rock Draw the picture on your notes – which fossil is older? _____ Fossil A Fossil B B

RADIOACTIVE DATING The use of half-lives to determine the age of a fossil Radioactive decay occurs at a constant rate called a HALF-LIFE (the time it takes for half of the atoms in a sample to undergo radioactive decay) EX. The half-life of Potassium-40 is 1.26 billion years Ex. The half-life of Carbon-14 is 5730 years Potassium dating is used for rocks that are suspected to be billions of years old and carbon dating is used for younger fossils (50,000 years)

EXAMPLE PROBLEM: Suppose there are 16 grams of Carbon-14 in a living snail shell and 4 grams of Carbon-14 in a fossilized snail shell How many half-lives has this fossil gone through? 2 What is the age of the fossil if each half-life of Carbon-14 takes 5730 years? 5730 X 2 = 11,460 How many grams of Carbon-14 will be left if the snail shell goes through one more half-life ? 2 grams

GEOLOGIC TIME SCALE In order to catalog the 4 billion years of life on Earth, scientists have created the geologic time scale to represent evolutionary time The scale is divided into large time spans called ERAS, which is subdivided into PERIODS

GEOLOGIC TIME SCALE BEGINEND MOST RECENT OLDEST

MASS EXTINCTION When majorities of species were eliminated during a time period very quickly Ex. Dinosaurs during the Cretaceous mass extinction These mass extinctions can have various causes: volcanoes, change in atmosphere, lands shifting, large comet or asteroid, weather changes