Transcript Chapter 12 History of Life

Chapter 12 History of
Life
12-1 How Did Life Begin
How old is the Earth?
4.5 to Billion Year Old!
How do we know?
Radiometric Dating
Calculating the age of an object
by measuring the proportions of
the radioactive isotopes of certain
elements
Radioisotopes are unstable
elements
They decay, or break apart
We measure decay using the
half-life of the element
Half-life means how long it takes
for half the atoms of a given
radioisotope to decay
Different half-life # for different
elements
Life From ??
Life on planet Earth came from two
possible sources.
Most likely is Spontaneous Origin, life
developing from organic molecules
reacting with the environment
Where do we get organic molecules?
Deep Sea Hydrothermal Vents
Extraterrestrial Seeding
Frozen Ocean Theory
Conditions of Early Earth
THE EARLY ATMOSPHERE
Possible gasses: H2O, NH3, CH4, H2,
CO2.
Ammonia would have broken down:
2NH3 into N2 + 3H2 (escaped to
space)
Final content was probably H2O
vapor, CO2 and CO, N2 (80%).
NO OXYGEN
REQUIREMENTS FOR LIFE
1. Lack of oxygen (reducing atmosphere).
2. Appropriate chemicals (water, organic
and inorganic molecules)
3. Sources of energy (U.V., heat, lightning)
4. Great amounts of time
NO ENZYMES WERE PRESENT
REACTIONS WERE SLOW
Oparin and Haldane
1920s
Hypothesized steps of
chemical evolution from
primitive earth conditions.
Led to the Primordial Soup
Model
Miller and Urey, 1953
Tested Oparin and Haldane’s
hypothesis.
Experiment - to duplicate
primitive earth conditions in
the lab.
Results
Organic monomers formed
including Amino Acids.
Problems With The Model
No ozone to protect the gases
in the atmosphere
UV radiation would have
destroyed ammonia and
methane
Bubble Model
Louis Lerman suggested that
the key process to form
organic chemicals occurred at
the ocean’s surface
What About Genetic
Information?
Genetic Information
DNA  RNA  Protein
Too complex for early life.
Other forms of genetic
information?
RNA Hypothesis
RNA as early genetic
information.
Rationale
RNA polymerizes easily.
RNA can replicate itself.
RNA can catalyze reactions
including protein synthesis.
What About Cell
Membranes?
Short chains of amino acids
can lead to microspheres
Coacervates
Colloidal droplets of proteins,
nucleic acids and sugars
surround by a water shell.
Will form spontaneously from
abiotically produced organic
compounds.
12-2 Development of Life
Oldest fossils are 3.5 Billion Years Old
They are prokaryotes
First prokaryotes were heterotrphs then
autotrophs
Cyanobacteria were among the first
photosynthetic bacteria
Responsible for free oxygen in the
atmosphere
Eubacteria are prokaryotes that contain
peptidoglycan
Archeabacteria are prokaryotes that do not
contain peptidoglycan
Evidence indicates that archeabacteria
were the 1st group to evolve
1st Eukaryotes
Appear about 1.5 Billion Years Ago
Mitochondria and Chloroplast
appearance explained by
endosymbiosis
These organelles are descended from
aerobic, symbiotic eubacteria
Both organelles have their own DNA
Multicellular Forms of Life
Have developed many times
Life grouped into 6 Kingdoms
Eubacteria and Archeabacteria
are single celled
Fungi, Plants, Protists, and
Animals have multicellular
organisms
Cambrian Explosion
When the most of the current
body plans 1st appear in the fossil
record
Most famous fossil find from this
time period was the Burgess
Shale
Mass Extinctions
Impact life because it reduces the
amount of competition for
resources
Allows for adaptive radiation to
occur
Almost every time period has one!
12-3 Progression of Life
Once the ozone layer formed, life
could invade the land
Ozone began to form around 2.5
BYA
Is formed when oxygen gas (O2)
becomes O3 from the radiation of
the sun
1st multicellular land organisms
were plants and fungi (Around
430 MYA)
Created a mutualistic
realationship
Means both benefit
Called mycorrhizae
Arthropods were the first animals
to invade land (After the plants
and fungi)
Arthropods have a hard
exoskeleton and jointed limbs
Examples include lobsters, crabs,
insects, arachnids, scorpions
Vertebrates followed arthropods
Vertebrates have a backbone
First ones were small, jawless fish
in the oceans
Then came the jawed fishes
Amphibians were the 1st land
vertebrates
Could breath air
Had better adaptations for thriving
on land than fish
Reptiles evolved from amphibians
Even more adapted to life on land
Had water tight skin, and shelled
eggs
Mammals and Birds evolved from
reptiles
Better adapted to the changes in
the climate at the end of the
Cretaceous
Time Periods in Order
Cambrian (Oldest)
Ordovician
Silurian
Devonian
Carboniferous
Permian
Triassic
Jurassic
Cretaceous
Tertiary
Quaternary (Present)