Chapter 14 The History Chapter 14 The History of Lifeof Life

14.1 Fossil Evidence of Change14.1 Fossil Evidence of Change

Earth’s Early HistoryEarth’s Early History Earth formed 4.6 billion years ago from Earth formed 4.6 billion years ago from

molten material.molten material. Cooled for 500 million years and formed a Cooled for 500 million years and formed a

solid crust on the surface. Surface is rich in solid crust on the surface. Surface is rich in lighter elements, as more dense elements were lighter elements, as more dense elements were pulled by gravity toward Earth’s center.pulled by gravity toward Earth’s center.

Atmosphere of Earth consisted of HAtmosphere of Earth consisted of H220, CO0, CO22, , SOSO22, CO, H, CO, H22S, HCN, NS, HCN, N22 and H and H22

Clues in RocksClues in Rocks A fossil is any preserved evidence of an A fossil is any preserved evidence of an

organism.organism. Most organisms decompose before they have a Most organisms decompose before they have a

chance to become a fossil.chance to become a fossil. Those organisms that are most likely to Those organisms that are most likely to

become fossilized are those that are covered become fossilized are those that are covered quickly by sediment (no Oquickly by sediment (no O22) and have hard ) and have hard parts.parts.

Only one in a million organism becomes a Only one in a million organism becomes a fossil.fossil.

Fossil FormationFossil Formation

Fossil FormationFossil Formation Fossils form in sedimentary rocks; sediments Fossils form in sedimentary rocks; sediments

cover the organism.cover the organism. Igneous rocks form from molten rock material; Igneous rocks form from molten rock material;

metamorphic rocks when other rocks are metamorphic rocks when other rocks are exposed to heat and pressure; both processes exposed to heat and pressure; both processes would destroy any fossil material in these rock would destroy any fossil material in these rock types.types.

Relative DatingRelative Dating Determine age of fossils Determine age of fossils

by comparing them with by comparing them with those in other layersthose in other layers

Law of Superposition Law of Superposition states that younger rock states that younger rock layers are deposited on layers are deposited on top of older rock layerstop of older rock layers

Only true of undisturbed Only true of undisturbed rock layersrock layers

Radiometric DatingRadiometric Dating Dating method that used the decay of Dating method that used the decay of

radioactive isotopes to measure the age of a radioactive isotopes to measure the age of a rock.rock.

Isotope is a form of an element that has the Isotope is a form of an element that has the same atomic number but a different atomic same atomic number but a different atomic mass (mass number)mass (mass number)

Half life is the amount of time it takes for ½ of Half life is the amount of time it takes for ½ of the original radioactive isotope to decay or the original radioactive isotope to decay or change into its decay productchange into its decay product

Radiometric DatingRadiometric Dating Commonly used radioactive elements are Uranium-Commonly used radioactive elements are Uranium-

238 (U238 (U238238), Potassium-40 (K), Potassium-40 (K4040) and Carbon-14 (C) and Carbon-14 (C1414)) Some radioactive isotopes used for radiometric dating Some radioactive isotopes used for radiometric dating

are found only is igneous or metamorphic rocks (not are found only is igneous or metamorphic rocks (not sedimentary) so isotopes cannot be used to date rocks sedimentary) so isotopes cannot be used to date rocks that contain fossils. Relative dating of fossils from that contain fossils. Relative dating of fossils from known igneous or metamorphic rocks are used.known igneous or metamorphic rocks are used.

CC1414 can be used to date fossils directly if they are less can be used to date fossils directly if they are less than 60,000 years oldthan 60,000 years old

Radiometric decay Rate of CRadiometric decay Rate of C1414 to N to N1414

Half life 5730 yearsHalf life 5730 years

Radiometric decay Rate of URadiometric decay Rate of U238238 to to PbPb205205

Half life 4520 million years (4.510 billion)Half life 4520 million years (4.510 billion)

The Geologic Time ScaleThe Geologic Time Scale Model that expresses the major geological and Model that expresses the major geological and

biological events in Earth’s history.biological events in Earth’s history. Largest time classification is the eon.Largest time classification is the eon. Eons are divided into erasEons are divided into eras Eras are divided into periodsEras are divided into periods Periods are divided into epochsPeriods are divided into epochs See page 397See page 397

Plate TectonicsPlate Tectonics During the Mesozoic era the location of the During the Mesozoic era the location of the

Earth’s plates underwent a major shift in Earth’s plates underwent a major shift in position and are continuing to move todayposition and are continuing to move today

Chapter 14 The History Chapter 14 The History of Lifeof Life

14.2 The Origin of Life14.2 The Origin of Life

Origin: Early IdeasOrigin: Early Ideas Spontaneous generation is the idea that life Spontaneous generation is the idea that life

arises from nonlife.arises from nonlife. People believed that it rained frogs, mice People believed that it rained frogs, mice

spontaneous arose out of grain, and from mud spontaneous arose out of grain, and from mud came insects, fish and worms.came insects, fish and worms.

Francisco Redi 1668Francisco Redi 1668 First controlled experiment to disprove spontaneous First controlled experiment to disprove spontaneous

generation in which flies arose out of meat.generation in which flies arose out of meat. He hypothesized that flies, not meat, gave rise to fliesHe hypothesized that flies, not meat, gave rise to flies

Louis Pasteur 1850’sLouis Pasteur 1850’s Experiment showed that sterile broth remained free of Experiment showed that sterile broth remained free of

microorganisms until exposed to air.microorganisms until exposed to air. Flasks still exist today free of microorganisms.Flasks still exist today free of microorganisms. Theory of spontaneous generation rejected and Theory of spontaneous generation rejected and

replaced with theory of biogenesis (life from life)replaced with theory of biogenesis (life from life)

Origin: Modern IdeasOrigin: Modern Ideas If life can only come from preexisting life If life can only come from preexisting life

(theory of biogenesis) then how did the first (theory of biogenesis) then how did the first life-form appear?life-form appear?

Three ideas:Three ideas: Divine creationDivine creation ExtraterrestrialExtraterrestrial Series of chemical eventsSeries of chemical events

Origin: Modern IdeasOrigin: Modern Ideas Simple organic molecules could have been Simple organic molecules could have been

formed from a mixture of gases present in the formed from a mixture of gases present in the early atmosphere when sparked by lightening.early atmosphere when sparked by lightening.

Theory proposed by Oparin and Haldren in Theory proposed by Oparin and Haldren in 1920’s1920’s

Called the “primordial soup”. The oceans as a Called the “primordial soup”. The oceans as a “soup” of chemicals that could have combined “soup” of chemicals that could have combined to form lifeto form life

Origin: Modern IdeasOrigin: Modern Ideas Simple organic Simple organic

molecules have been molecules have been formed in the laboratoryformed in the laboratory

Experiments of Miller Experiments of Miller and Urey in 1953.and Urey in 1953.

Amino acids, sugars and Amino acids, sugars and nucleotides have been nucleotides have been formed by refining this formed by refining this experiment.experiment.

Origin: Modern IdeasOrigin: Modern Ideas Another ideas is that the Another ideas is that the

organic reactions that organic reactions that preceded life’s preceded life’s emergence began at emergence began at deep-sea vents where deep-sea vents where sulfur forms the base of sulfur forms the base of a unique food chain.a unique food chain.

Origin: Modern IdeasOrigin: Modern Ideas

In order for life to form from nonlife (chemicals) In order for life to form from nonlife (chemicals) three requirements must be met: three requirements must be met: Making proteinsMaking proteins Genetic codeGenetic code Molecules to cellsMolecules to cells

Making ProteinsMaking Proteins In order for life to exist proteins must be formed.In order for life to exist proteins must be formed. Stable proteins can be formed on clay particlesStable proteins can be formed on clay particles

Genetic CodeGenetic Code A coding system for protein is a requirement A coding system for protein is a requirement

for life.for life. All living things have DNA and RNA.All living things have DNA and RNA. Since some RNA sequences have changed Since some RNA sequences have changed

little over time, scientists consider RNA to be little over time, scientists consider RNA to be the first genetic coding system.the first genetic coding system.

RNA can also act like an enzyme and could RNA can also act like an enzyme and could have carried out some early life processeshave carried out some early life processes

Thought that RNA replication took place on a Thought that RNA replication took place on a clay crystal.clay crystal.

Molecule to CellsMolecule to Cells Cells have a membrane.Cells have a membrane. Scientists have tested ways of enclosing Scientists have tested ways of enclosing

molecules in membranes, allowing early molecules in membranes, allowing early metabolic and replication pathways to develop.metabolic and replication pathways to develop.

How cells formed has yet to be explained.How cells formed has yet to be explained.

Cellular EvolutionCellular Evolution The first cells were prokaryotes similar to The first cells were prokaryotes similar to

current day archaebacteria.current day archaebacteria. Today archaebacteria live in extreme Today archaebacteria live in extreme

environments similar to what may have been environments similar to what may have been experienced on early Earth.experienced on early Earth.

Photosynthesis began by cyanobacteria (not Photosynthesis began by cyanobacteria (not archae). Until 1.8 billion years ago no oxygen archae). Until 1.8 billion years ago no oxygen existed in the atmosphere.existed in the atmosphere.

Fossils of these bacteria have been found and Fossils of these bacteria have been found and dated at 3.5 billion years old.dated at 3.5 billion years old.

Cellular EvolutionCellular Evolution Once cyanobacteria Once cyanobacteria

produced sufficient produced sufficient oxygen to form the oxygen to form the ozone layer, conditions ozone layer, conditions were right for the were right for the evolution of eukaryotic evolution of eukaryotic cells.cells.

Ozone layer protects Earth Ozone layer protects Earth from harmful radiationfrom harmful radiation

Cellular EvolutionCellular Evolution Eukaryotic cells appeared in the fossil record Eukaryotic cells appeared in the fossil record

about 1.8 billion years ago. (2 billion years about 1.8 billion years ago. (2 billion years after archae)after archae)

The endosymbiont theory suggests that some The endosymbiont theory suggests that some photosynthetic bacteria became engulfed photosynthetic bacteria became engulfed within a larger bacteria and became the within a larger bacteria and became the chloroplast; other engulfed bacteria became chloroplast; other engulfed bacteria became the mitochondria.the mitochondria.

Endosymbiont TheoryEndosymbiont Theory

Evidence for the Endosymbiont Evidence for the Endosymbiont Theory Theory

Both mitochondria and chloroplasts contain Both mitochondria and chloroplasts contain their own circular DNA just like prokaryotes.their own circular DNA just like prokaryotes.

Both mitochondria and chloroplasts contain Both mitochondria and chloroplasts contain ribosomes that closely resemble archae ribosomes that closely resemble archae ribosomes.ribosomes.

Like prokaryotic cells both mitochondria and Like prokaryotic cells both mitochondria and chloroplasts reproduce by fission, independent chloroplasts reproduce by fission, independent from the rest of the cell.from the rest of the cell.