Transcript The History of Life

The History of Life
History of the Earth
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Formed 4.6 billion year ago
Started as hot ball of rock
Earth cooled 4.4 bya
First life began between 3.9 and 3.4
bya
Fossils
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Evidence of an organism that lived
long ago
Paleontologists
• Study ancient life
• Uses fossils to:
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understand events that happened long ago
Determine the kinds of organisms that lived
during the past and their behaviors
Study ancient climate and geography
How fossils form
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Organisms are buried in mud, sand, or clay
Sediments cover the organism, slows
decomposition
Minerals from sediments seep into body
Over time, sedimentary layers compressed into
rock
Mineral replace the body’s bone material
Earth’s movement or erosion expose the body
Rocks form at relatively low temperatures and
pressure
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Prevent damage of organism
Types of Fossils
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Trace fossils
• An indirect evidence
left by an animal
• Include a footprint,
a trail, or a burrow
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Casts
• A replica or cast
• Minerals in rocks fill
a space left by a
decayed organism
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Molds
• An empty space left
by an organisms
after it decays
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Petrified
• Minerals penetrate
and replace the
hard parts of an
organism
Petrified
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Permineralized
• Void spaces in
original organism is
filled by minerals
Permineralized
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Amber-preserved
or frozen
• An entire organism
quickly trapped in
ice or tree sap and
hardens
Amber preserved
Frozen
Dating fossils
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Relative dating
• uses the position of fossils in sediment
layers
• oldest fossil at the bottom layer,
youngest on top
• Can only determine whether one fossil
is older than another
• Cannot determine the actual age
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Radiometric dating
• use radioactive isotopes (atoms with
unstable nuclei that break down or
decay)
• decay of each radioactive element is
known and continues at a steady rate
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Half-life
• the time it takes a radioactive element
to get to half its original amount
• Potassium 40 - 1.3 billion yrs
• Carbon 14 - 5730 years
Geologic Time Scale
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a type of calendar
based on the
different types of
living organisms
that have appeared
on Earth
Precambrian Era
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Starts 4.7 bya
Accounts for 87% of Earth’s history
Oldest rock dates 3.4 bya
Unicellular prokaryotes appeared
Eukaryotes appeared 2.1 bya
Ended 345 mya
Oldest rock from Yukon, 4 byo
Paleozoic Era
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345 to 248 mya
Appearance of plants and animals including
fishes, reptiles, amphibians and ferns
90% of Earth’s marine species and 70% of land
species disappeared
Mesozoic Era
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248 to 65 mya
• Triassic
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Oldest
Mammals appeared
Dinosaurs first
appeared
• Jurassic
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Age of dinosaurs
• Cretaceous
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Mammals and
flowering plants
Dinosaurs and 2/3 of
living species
became extinct
Theory of Continental Drift
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Continents were joined in a landmass
known as Pangaea
Pangaea broke apart resulting in two
large masses
At the end of the Mesozoic, most of
the continents had taken on their
modern shapes
Explained by plate tectonics
• Movement of the continents
The Origin of Life
The Early Ideas
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Spontaneous generation
• Nonliving material can produce life
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Experiments to disprove this theory
• Francesco Redi
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Used maggots in covered and uncovered
jars
• Louis Pasteur
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Used curved flasks with heated broth
Francesco Redi
• 1668
• Showed that rotting
meat kept away
from flies would not
produce new flies
• Maggots appeared
only on meat that
had been exposed
to flies
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Eggs laid on meat
Louis Pasteur
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Mid- 1800s
Used curve-necked
flasks
Microorganisms were
prevented from
entering the flask
When curved necks
were broken, broth
became cloudy with
microorganims
Biogenesis
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All living things come from other
living things
Became cornerstone of biology after
Pasteur’s experiment
The Modern Ideas
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Alexander Oparin
• Life began in the oceans that formed on
early Earth
• Energy from sun + lightning+ Earth’s
heat = simple compounds (eg. amino
acids)
• Earth cooled, water vapor condensed to
form lakes and seas, compounds
collected in the water
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Stanley Miller and
Harold Urey
Used Oparin’s
hypothesis to setup
experiment
Produced amino
acids and other
organic compounds
Formation of Protocells
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Sidney Fox
Produced protocells
• Large, ordered
structure, enclosed
by a membrane
• Carries out some life
activities (growth
and division)
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Heated amino acids
The First True Cells
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Prokaryotes evolved from a protocell
• Heterotrophs
• Anaerobic
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Archaebacteria
• Prokaryotic
• Autotrophs
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Made glucose by chemosynthesis
• Lived in harsh environments
• Deep-sea vents and hot springs
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Photosynthesizing prokaryotes
• Increased oxygen in atmosphere
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Eukaryotes evolved from prokaryotes
Endosymbiont Theory
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Eukaryote provided beneficial
environment
Prokaryote provided method of
energy synthesis
Endosymbiotic, aerobic prokaryotes
evolved into modern mitochondria
Photosynthetic cyanobacteria
evolved into chloroplasts
Endosymbiosis Theory