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The History of Earth and Life
Fossils & Ancient Life
 The study of ancient life using fossil records
 Paleontologist-A scientist who studies fossils to infer what
past life and life forms were like.
 Fossil Record- Collection of fossils used as information about
past life.
 Provides evidence about the history of life on Earth.
 Shows how different groups of organisms changed over time.
 99% of all species that have ever lived on earth have become extinct.
How Fossils Form
 The Steps to fossil formation
 Water carries small rock particles to the bottom of lakes and
 Dead organisms at the bottom of lakes and seas are buried by
the layers of sediment which forms new rock.
 The weight of the new rock compresses on the lower layers
of the new rock and minerals replace all or part of the dead
organisms body
 The preserved remains may later become exposed due to a
variety of factors.
 Most fossils form in sedimentary rock.
Interpreting Fossil Evidence
 Relative Dating: The age of a fossil is estimated by comparing
the fossil to other fossils.
 Index Fossils- Those fossils used for comparison purposes in relative
dating. These fossils are distinctive fossils from specific time periods.
 This type of fossil dating provides no information about absolute age
of the fossil
 Radioactive Dating: The age of the fossil is calculated based on
the amount of remaining radioactive isotopes it contains.
 Half-life- the length of time it takes for half of the radioactive atoms in
a sample to decay.
 Radioactive dating uses half-lives to determine the age of the fossil.
Geologic Time Scale
 Scale used to represent evolutionary time.
 Major changes on fossil records of plants and animals are
used to mark where one segment ends and another begins.
 The basic divisions of the scale are
 Eras & Periods
Formation of Earth
 Earth was created approximately 4.6 billion years ago.
 Clouds and dust condensed into a sphere.
 Gravity pulled this cosmic debris (matter) together to form a
 Collisions with other objects ( some as large as planets)
produced enough heat to melt the globe.
 After the earth melted its elements rearranged themselves
according to density.
Formation of Earth Cont…
 4 Billion years ago Earth cooled.
 Volcanic eruptions and meteor showers brought the materials to
earth to create solid rock.
 3.8 Billion years ago the Earth’s surface cooled off enough
for water to remain in liquid form.
 Oceans form.
 Earths original atmosphere lacked oxygen to support life.
The First Organic Molecules
 Stanley Miller and Harold Urey conducted laboratory
simulations of early earth to explain how early organic
molecules emerged from simpler compounds.
 Energy from an lightning strike may have provided the electrical
spark needed to combine atoms of the atmosphere and form
molecules necessary for life on Earth to exist.
 Earth can now produce organic molecules like carbohydrates,
proteins, lipids and amino acids.
The Puzzle of Life’s Origin
 Formation of Microspheres
 Under certain conditions large macromolecules can form tiny
bubbles called proteinoid microspheres, which can exhibit the
properties of cells.
 Some scientists believe these microspheres took on more and more of
the cells characteristics and eventually became what we know of as
 Evolution of RNA and DNA
 Neither DNA or RNA can exist without each other.
 So which can first??????
 Scientists think RNA existed first and gave way to DNA
 However, many questions still exist about the evolution of DNA and RNA.
Free Oxygen
 Microfossils- fossils of microscope organisms found in rock
3.5 million years ago.
 These organisms were single celled prokaryotic organisms
known as anaerobes(organisms that lived without oxygen).
 Anaerobes today exist in airless environments.
 Photosynthetic bacteria evolved and began to put oxygen into
the atmosphere.
 Gives way to aerobes (organisms that need oxygen).
 Many anaerobes died because oxygen was toxic to them.
 Ozone layer now forms.
Origin of Eukaryotic Cells
 Prokaryotic cells (those cells that don’t have a nucleus) gave
way to Eukaryotic cells (those cells that do have a nucleus).
 Endosymbiotic Theory- Eukaryotic cells formed from a
symbiosis among several different prokaryotic organisms.
 Sometime after eukaryotic cells emerged they began to
reproduce sexually which allowed evolution to speed up.
Evolution of Multi-cellular Life
 Eras:
 Periods:
Patterns of Evolution
 Macroevolution: The large scale evolutionary patterns and
processes that occur over long periods of time.
 Extinction: The elimination of the existence of a species.
 Natural selection has caused 99% of all species to go extinct.
 Mass extinction- the extinction of an entire ecosystem.
 Serious large event that causes the mass extinction.
 Dinosaurs wiped out this way.
 Clears the way for the evolution of modern species like mammal and
Patterns of Evolution Cont….
 Adaptive Radiation: Process by which a single species or
group of species evolves into several different forms that live
in different ways.
 Leads to rapid growth in diversity
 Convergent Evolution: Process by which unrelated
organisms independently evolve similarities when adapting to
similar environments.
Patterns of Evolution Cont….
 Co-evolution: The process by which two species evolve in
response to change in each other over time.
 EX: Plants and the insects that pollinate them.
 Punctuated Equilibrium: Describes pattern of long
stable periods interrupted by brief periods of more rapid
 Gradualism: Slow, steady, gradual change.
Developmental Genes and Body Plans
 Small changes in the activity of control genes that can many
other genes and cause larger changes in adult animals.
 Changes caused by changes in activation genes.
 EX: Many pairs of wings on ancient insects but only a single pair
of wings on modern insects.