• Become familiar with the Geologic Time
Scale by assessing eras and periods of when biological events occurred.

Objectives
• Describe a typical sequence of events of fossilization
• Compare techniques for dating fossils
• Identify and describe major events using the geologic time scale.

Chapter 14 The History of Life
14.1 Fossil Evidence of Change
Land Environments
 Earth formed about 4.6 billion years ago.
 Gravity pulled the densest elements to the center of the planet.
 After about 500 million years, a solid crust formed on the surface.

Chapter 14 The History of Life
14.1 Fossil Evidence of Change
Atmosphere
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Chapter 14 The History of Life
14.1 Fossil Evidence of Change
Clues in the Rocks
 A fossil is any preserved evidence of an organism.
 Plants, animals, and bacteria can form fossils.
 Approx. 99% of the species that have ever lived are now extinct but only a tiny % of those organisms are preserved as fossils.
Most organisms decompose before they have a chance to become fossilized.

Chapter 14 The History of Life
14.1 Fossil Evidence of Change

Chapter 14 The History of Life
14.1 Fossil Evidence of Change
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.

Chapter 14 The History of Life
14.1 Fossil Evidence of Change
Dating fossils
 Relative dating is a method used to determine the age of rocks by comparing them with those in other layers.
 Relative dating is based on the law of superposition which states that younger layers of rock are deposited on top of older layers. i.e. stack of newspapers

Chapter 14 The History of Life
14.1 Fossil Evidence of Change
Radiometric Dating
 Uses the decay of radioactive isotopes to measure the age of a rock
 Radioactive isotopes that can be used for radiometric dating are found only in igneous or metamorphic rocks.

• An isotope is a form of an element that has the same atomic number but a different mass number.
• Uranium 238 is an element commonly used to determine the age of rocks.
• When testing a rock sample, scientists calculate the ratio of the parent isotope to the daughter isotope to determine the age of the sample. i.e
U238 decays to Pb 206 with a half life of 4510 million years.
• Carbon 14 is used to date organic substances such as bones and tissue

Chapter 14 The History of Life
14.1 Fossil Evidence of Change
The Geologic Time Scale
 The geological time scale is a model that expresses the major geological and biological events in Earth’s history.
 The geologic time scale is divided into the
Precambrian time and the Phanerozoic eon.
 Eras of the Phanerozoic eon include the
Paleozoic, Mesozoic, and Cenozoic eras.
 Each era is divided into one or more periods.

Visualizing the Geologic Time Scale
• http://glencoe.mcgrawhill.com/olcweb/cgi/pluginpop.cgi?it=swf::550
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4_Visualising_the_Geologic_Time_scale.swf
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Chapter 14 The History of Life
14.1 Fossil Evidence of Change
Precambrian
 Nearly 90 percent of Earth’s entire history, stretching from the formation of Earth to the beginning of the Paleozoic era about
542 million years ago
 Autotrophic prokaryotes enriched the atmosphere with oxygen. Eukaryotic cells emerged, and the first animals had appeared.
 Extensive glaciations marked 2 nd half of the Precambrian

Chapter 14 The History of Life
14.1 Fossil Evidence of Change
The Paleozoic Era
 The ancestors of most major animal groups diversified in what scientists call the Cambrian explosion.
 Life in the oceans continued to evolve at the end of the Cambrian period .
 Fish, land plants, and insects appeared during the Ordovician and Silurian periods.
 The first tetrapods emerged in the Devonian. i.e. Frogs
 Mass extinction ended the era

Chapter 14 The History of Life
14.1 Fossil Evidence of Change
The Mesozoic Era
 Mammals and dinosaurs first appeared late in the Triassic period, and flowering plants evolved from nonflowering plants.
 Birds evolved from a group of predatory dinosaurs in the middle of the Jurassic period.
 About 65 million years ago , a meteorite struck Earth. Evidence of this impact lies in the K-T boundary, which is a layer of rock.

Chapter 14 The History of Life
14.1 Fossil Evidence of Change
The Cenozoic EraThe most recent era
 Mammals became the dominant land animals.
 After the mass extinction at the end of the
Mesozoic era, mammals of all kinds began to diversify.

Chapter 14 The History of Life
14.1 Fossil Evidence of Change
Continental Drift
 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.

Chapter 14 The History of Life
http://www.natgeoeducationvideo.com/film/1042/continental-drift

• http://videos.howstuffworks.com/sciencechannel/29145-100-greatest-discoveriesradiometric-dating-video.htm

• Procedure:
• 1. Arrange pennies so that their “head sides are facing up. Each “head” represent an atom of K40, and each “tail” represents an atom of Ar40.
• 2. Record the number of “heads” and “tails” present at the start of the experiment. Use the row marked 0 in the data table.
• 3.Cover the box and shake well. The shake represents ½ life of K40, which is 1.3 billion years.

• 4. Remove the lid and record the number of “heads” you see facing up. Remove all the “tail” pennies.
• 5. Complete Trial 1 by shaking and counting until you have reached 5 ½ lives.
• 6.Run two more trials and determine an average for the number of “heads” present at each half life.
• 7. Draw a graph. Plot your average values on the graph.
Plot the number of half-lives for K 40 on the x-axis and the number of “heads” on the y-axis.
• 8. Remember, each half-life mark on the graph axis for
K40 represents 1.3 billion years.
• 9.Remember a title and key for your graph!


• Visit the website:
• http://phet.colorado.edu/en/simulation/radioa ctive-dating-game
• Click on the green button: RUN NOW
• List 3 things that you didn’t know about dating fossils, that you now understand.
• List 2 things that you thought were neat about the site.
• List 1 thing that you would like clarified.

Objectives
• Differentiate between spontaneous generation and biogenesis
• Sequence the events that might have led to cellular life
• Describe the endosymbiotic theory

Chapter 14 The History of Life
14.2 The Origin of Life
Origins: Early Ideas
 Spontaneous generation is the idea that life arises from nonlife.
 Francesco Redi, an Italian scientist, tested the idea that flies arose spontaneously from rotting meat.

Chapter 14 The History of Life
14.2 The Origin of Life
 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.

Chapter 14 The History of Life
14.2 The Origin of Life
Origins: Modern Ideas
 Simple organic molecule formation
 The primordial soup hypothesis was an early hypothesis about the origin of life .
 Organic molecules could have been synthesized from simple reactions.
 UV light from the Sun and electric discharge in lightning might have been the primary energy sources .

Chapter 14 The History of Life
14.2 The Origin of Life
 Stanley Miller and Harold
Urey were the first to show that simple organic molecules could be made from inorganic compounds .
 The resulting mixture was found to contain amino acidsthe building blocks for proteins. This supported the primordial soup hypothesis. http://highered.mcgrawhill.com/sites/9834092339/student_view0/ch apter26/animation_-_millerurey_experiment.html

Chapter 14 The History of Life
14.2 The Origin of Life
Making Proteins
 Life requires proteins .
 One possible mechanism for the formation of proteins would be if amino acids were bound to a clay particle.

Chapter 14 The History of Life
14.2 The Origin of Life
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.

Chapter 14 The History of Life
14.2 The Origin of Life
Cellular Evolution
 Scientists hypothesize that the first cells were prokaryotes. Recall* prokaryotes are smaller than eukaryotes, and lack a defined nucleus.
Many scientists think that modern prokaryotes called archaea are the closest relatives of Earth’s first cells.

Chapter 14 The History of Life
14.2 The Origin of Life
Photosynthesizing Prokaryotes
 Archaea are autotrophic, and are considered to be the earliest forms of terrestial life.
 They do not obtain their energy from the Sun .
• Archaea also do not need or produce oxygen.
 They are extrempohiles.

Chapter 14 The History of Life
14.2 The Origin of Life
 Many scientists think that photosynthesizing prokaryotes evolved not long after the archaea.
 Prokaryotes, called cyanobacteria, have been found in rocks as old as 3.5 billion years.
 Cyanobacteria are aquatic bacteria, and manufacture their own food- photosynthetic.

Chapter 14 The History of Life
14.2 The Origin of Life
The Endosymbiont Theory
 The ancestors of eukaryotic cells lived in association with prokaryotic cells.
 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.

Chapter 14 The History of Life
14.2 The Origin of Life