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The History of Life
Biology
Early History of Earth
• Earth’s Atmosphere was
probably composed of CO2
and Nitrogen. But with the
continuous eruptions of the
volcanoes led to the formation
of the atmosphere.
• After it cooled about 4.4
billions ago, water condensed,
and precipitation was released
and the oceans were formed.
• Scientist believe that this
occurred about 3.9 and 3.4
billion years ago.
Fossils-Clues from the past
• Earth holds a large
diverse group of life.
• This is a small fraction of
the species that ever
existed.
• About 95% of the species
that have existed are
extinct.
• Fossils is one form that
scientist use to study
ancient species.
• A fossil is evidence of an
organism that lived long
ago.
Types of Fossil
• Trace fossils- Indirect
evidence, example a footprint,
a trail or burrow.
• Casts- when minerals in rocks
fill a space left by decayed
organisms.
• Molds- when an organism is
buried in sediments and then
decays and leaves an empty
space.
• Petrified- minerals replace
hard parts of the organism.
• Amber/Frozen- entire
organism is trapped.
Relative Dating
• A technique used to determine
the age of fossils.
• If rock layers are left
undisturbed, the scientist is
able to give the relative age of
fossils.
• They do this by determining
that older rocks are found in
the bottom of layers compared
to those found on top.
• Not very accurate because of
natural changes that occur on
Earth.
Radioactive dating
• This technique is used to find the specific age of rocks.
• Fossils and sedimentary rocks cannot be radiometrically
dated.
• Most dates are for volcanic and other igneous rocks, or
metamorphic rocks closely related to sedimentary rocks.
• A method for determining the age of an object based on the
concentration of a particular radioactive isotope contained
within it. For inorganic materials, such as rocks containing the
radioactive isotope rubidium, the amount of the isotope in the
object is compared to the amount of the isotope's decay
products (in this case strontium). The object's approximate
age can then be figured out using the known rate of decay of
the isotope. For organic materials, the comparison is between
the current ratio of a radioactive isotope to a stable isotope of
the same element and the known ratio of the two isotopes in
living organisms. Radiocarbon dating is one such type of
radiometric dating.
Diversity of Precambrian
•
•
•
•
•
•
Some rocks date back to about
3.4 billion years ago.
87% of the Earth’s history is spent
in the Precambrian Time.
Type of life that existed then were
Stromatolites. Organisms similar
to modern day cyanobacteria.
Cyanobacteria is a photosynthetic
water organism.
These organism were prokaryotic.
Unicellular organisms with no
membrane bound orgnalles.
Eukaryotic organisms appeared
about 2.1 billion years ago.
Multicellular organisms appeared
about the end of Precambrian (
543 million years ago)
Diversity of the Paleozoic
•
•
•
•
•
•
•
•
Lasted until about 248 million
years ago.
Earth had a larger diversity of life.
Earliest part of the Paleozoic is
called Cambrian.
The oceans contained many
organisms like worms, sea stars
and arthropods.
First half of Paleozoic had fish and
animals with back bone and ferns.
Mid Paleozoic four legged animals
appeared.
Last half reptiles appeared and
flourish on land.
The end of the Paleozoic is
marked as the largest mass
extinction of species. 90% marine
animals and 70% land species
dissappeared.
Life in the Mesozoic
• Began 248 million years ago.
• Many geological and organism
changes occurred during this
Era.
• Divided into 3 Periods
– Triassic- oldest period
mammals appeared. Thought
to small and mouselike.
– Jurassic- 206 million years
ago. Modern birds evolved
from one group of dinosaurs.
– Cretaceous- Last period,
began 144 million years ago.
Mass extinction of dinosaurs
but many new types of
mammals and plants
appeared.
Changes during the Mesozoic
• Geological events
changed the Earth’s
land.
• Continental Drift
occurred and
changed where
animals lived.
• Theory of Plate
Tectonics
The Cenozoic Era
• Began 65 million years
ago.
• Tertiary-Mammals began
to flourish along with a
group of animals
somewhat related to you.
The primate group first
appeared about 65
million years ago.
• Quaternary-The human
species appeared about
200,000 years ago.
Mass Extinctions
• Extinction- death of all members of a species
• Mass extinction- episode during which large
numbers of species become extinct
• Ordovician period 440 million years ago was the
first mass extinction
• Second mass extinction= 360 million years
• Third mass extinction = 245 million years ago
– Most devastating loosing 96% of all species


Fourth mass extinction= 200 million years ago
Fifth mass extinction = 65 million years ago- dinosaurs
The Origin of Life
• Spontaneous
Generation: the idea
that nonliving material
can produce life.
FRANCESCO REDI’S EXPERIMENT 1668
REDI’S EXPERIMENT SHOWED THAT FLIES WERE
THE PRODUCT OF BIOGENESIS. HE DEMONSTRATED
THAT FLIES DIDN’T ARISE FROM ROTTING MEAT,
BUT WERE THE OFFSPRING OF FLIES DRAWN TO THE
ROTTING MEAT.
Louis Pasteur
• Disproved the
spontaneous
generation of
microorganisms.
• After disproving it, the
idea of biogenesis
was accepted.
• Biogenesis- living can
only come from other
living things.
Alexander Oparin
• Hypothesized that life
formed in the oceans.
Through energy from the
sun, lightning, and Earth’s
heat triggered chemical
reactions to form small
organic molecules from
substances in the air.
Then the rain formed this
primordial soup.
Miller and Urey
• Tested Oparin’s
Hypothesis by
simulating Earth’s
Early atmosphere (
ammonia, water
vapor, methane, and
hydrogen gases.
They sent electric
currents to simulate
lightning and this
created several
kinds of amino
acids, sugars, and
small organic
molecules.
Sidney Fox and The formation of
Protocells
• This occurred when these
amino acids were heated
and proteins formed.
• American Biochemist
Sydney Fox tested this
hypothesis by heating
solutions of amino acids
and forming protocells.
• A protocell is a structure
enclosed in a membrane
that carries out some life
activities, such as growth
and division.
The Evolution of Cells
• Even though the
geological scale shows
prokaryotes as the first
life to exist. They were
probably anaerobic.
• They were considered to
be heterotrophs because
the ate the molecules
formed in oceans.
• Through this process
autotrophs probably
formed. These were
archeabacteria.
The Evolution of Cells
• Eventually photosynthesizing organisms formed.
They were the ones that released oxygen into
the atmosphere.
• This eventually formed the ozone layer that gave
protection from UV rays. This enabled the
formation of complex organisms.
• The Endosymbiont Theory: Complex
Eukaryotes formed from prokaryotic organisms.
This occurred by ancient prokaryotic organisms
having close relationship with simple
eukaryotes.
Cellular Life Begins
• Fossil – preserved or mineralized remains
(bone, tooth, or shell) or imprint of an
organism that lived long ago
• Prokaryotes- single celled organisms 2.5
billion years old.
– Lack internal membrane bound organelles
Dr. Lynn Margulis
• 1966
• Endosymbiosis
• Mitochondriadescendants of
symbiotic, aerobic
eubacteria
• Chloroplasts are
descendants of
symbiotic,
photosynthetic
eubacteria
Mitochondria and Chloroplasts
• Both have circular DNA similar to bacteria
chromosomes
• Both have genes that are different from the host
cell
• Both have ribosomes that are similar to
bacterial ribosomes
• Reproduce by fission
• Replication is independent of the host cell cycle