Transcript History of Life on Earth

History of Life on Earth
Objectives
Summarize how radioisotopes can be used to
determine the age of the earth
Compare two models that describe how the
chemicals of life originated
Describe how cellular organization might have
begun
Age of the Earth
Scientist believe that the
earth originated 4.5
billion years ago
They speculate that it
was a fiery ball of molten
rock that cooled into a
solid rock
Water vapor in the
atmosphere condensed
to form the vast oceans
of the planet
Most scientists believe
that life began in these
oceans
Radiometric Dating
Radiometric Dating: A process of measuring the age of
an object by determining its concentration of certain
radioactive isotopes
Scientists estimate the age of the earth through a
process called radiometric dating
Law of Superposition
A general law stating that
in any sequence of
sediments or rocks that
has not been overturned,
the youngest sediments
or rocks are at the top of
the sequence and the
oldest are at the bottom
Half-Life
The time it takes for onehalf of a given amount of
radioisotopes to decay
By measuring the
proportions of certain
radioisotopes and their
decay, scientists can
compute how many halflives have passed since
a rock was formed
Formation of Chemical
Life
Scientist believe that life began as a random
series of chemical and physical processes.
It is thought that life began when non-living
chemicals reacted chemically during the first
billion years of the earth's history
Primordial Soup Model
Scientists A.I. Oparin and
J.B.S. Haldane
Suggests that the ocean
was filled with many
different organic
molecules
Theorized that molecules
spontaneously formed in
chemical reactions
powered by lightening,
volcanoes and solar
radiation
Urey-Miller Model
1953 Stanley Miller tests
Primordial Soup theory
He created complex
organic molecules using
the basic gases found in
the earth's ocean
However...
It was later determined that the earth did not
posses an ozone layer.
The ozone layer protects the earth from the
sun's ultraviolet rays
Without the layer of protection the rays would
have destroyed any complex molecules created
by the primordial soup model
Bubble Model
If gases necessary for life
to evolved had not
existed in the
atmosphere, where did
they come from?
1986 Louis Lerman
suggested that the gases
were trapped in bubbles
on the surface of the
ocean
Bubble Model
Simple organic
molecules from number
eruptions of undersea
volcanoes were trapped
in bubbles
Inside the bubbles gases
underwent chemical
reactions due to the
concentration of the
chemicals
Bubble Model
Bubbles rose to the
surface and burst
releasing the organic
molecules into the air
Up in the air, the organic
molecules were exposed
to ultraviolet radiation
and lightening which
provided energy for more
reactions
Bubble Model
More complex organic
molecules formed by
further reactions fell into
the ocean with rain,
starting another cycle