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CHAPTER 14 NOTES
Land Environments
 Earth formed about 4.6 billion years ago.
 Gravity pulled the densest elements to the center of the planet.
 The planet began to cool after about 500 million years.
 A solid crust formed on the surface.
 Water vapor condensed and formed the oceans.
 Most scientists believe life began in the oceans
Atmosphere
 The gases that likely made up the atmosphere are those that were expelled by volcanoes.
 Water vapor, Carbon dioxide, Sulfur dioxide, Carbon monoxide, Hydrogen sulfide, Hydrogen cyanide, Nitrogen,
and Hydrogen
 NO Oxygen (O2)
Radiometric Dating
 Uses the decay of radioactive isotopes to measure the age of a rock
 Radioactive dating is the method used to determine the age of the earth and of fossils.
Clues in Rocks
 A fossil is any preserved evidence of an organism.
 Examples of fossils include bones, shells, and impressions of dead organisms left in rocks.
 Most organisms decompose before they have a chance to become fossilized.
Fossil Formation
 Nearly all fossils are formed in sedimentary rock.
 The sediments build up until they cover the organism’s remains.
 Minerals replace the organic matter or fill the empty pore spaces of the organism.
Dating fossils
 Relative dating is a method used to determine the age of rocks by comparing them with those in other layers.
 Plate tectonics describes the movement of several large plates that make up the surface of Earth.
 These plates, some of which contain continents, move atop a partially molten layer of rock underneath them.
Origins: Early Ideas
 Spontaneous generation is the idea that life arises from nonlife.
 Francesco Redi, an Italian scientist, disproved the idea that flies arose spontaneously from rotting meat.
 The theory of biogenesis states that only living organisms can produce other living organisms.
 Louis Pasteur designed an experiment to show that biogenesis was true even for microorganisms.
Simple Organic Molecule Formation
 Life may have began at the surface of the ocean where UV light from the Sun and lightning were the primary energy
sources.
 Many scientists believe life began at the depths of the ocean where geothermal vents provided the energy for organic
molecule formation.
The Primordial Soup Model
 In the 1920’s Oparin and Haldane both suggested that the early Earth’s oceans contained large amounts of organic
molecules.
 This hypothesis became known as the primordial soup model.
 In 1953, the primordial soup model was tested by Miller and Urey.
 Stanley Miller and Harold Urey were the first to show that simple organic molecules could be made from inorganic
compounds.
 Later, scientists found that hydrogen cyanide could be formed from even simpler molecules in simulated early Earth
environments.
The Bubble Model
 In 1986, the geophysicist Louis Lerman suggested that the key processes that formed the chemicals needed for life took
place within bubbles on the ocean’s surface.
Genetic Code
 Some RNA sequences appear to have changed very little through time.
 Many biologists consider RNA to have been life’s first coding system.
 Other researchers have proposed that clay crystals could have provided an initial template for RNA replication.
Cellular Evolution
 Scientists hypothesize that the first cells were prokaryotes.
 Many scientists think that modern prokaryotes called Archaea are the closest relatives of Earth’s first cells.
Photosynthesizing Prokaryotes
 Fossil evidence of cyanobacteria has been found in rocks as old as 3.5 billion years.
 Cyanobacteria eventually produced enough oxygen to support the formation of the ozone layer.
 Ozone blocks the sun’s UV rays
 With oxygen and the ozone layer in the atmosphere, life could migrate onto land.
The Endosymbiotic Theory
 The ancestors of eukaryotic cells lived in association with prokaryotic cells.
 It has been suggested that a large prokaryote engulfed a smaller one, which continued to live and provide
energy to the larger prokaryote
 The relationship between the cells became mutually beneficial, and the prokaryotic symbionts became organelles in
eukaryotic cells.
 This theory explains the origin of chloroplasts and mitochondria.