Earth`s Early History
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Transcript Earth`s Early History
Chapter 17.2:
Earth’s Early History
Age of the Earth
It is estimated that the Earth
is 4.6 billion years old
– Theories of how the Earth was “born”
vary (IE – the Big Bang Theory)
– Elements arranged themselves according
to density
Least dense make up the atmosphere, most
dense make up the core
Earth’s Early
Atmosphere
Earth’s early atmosphere probably
contained hydrogen cyanide, carbon
dioxide, carbon monoxide, nitrogen,
hydrogen sulfide, and water
– All toxic gases except the
water
The Early Earth
4 billion years ago the first solid rocks
formed
3.8 billion years ago that the Earth was
cool enough to have liquid water
– So this is when the first oceans formed
Earth BEFORE oceans
formed
Characteristics of Earth before oceans
formed:
Comets and asteroids
Volcanic activity
Atmosphere of poisonous gas
Why do you think
oceans did not exist on
Earth 4 billion years
ago?
Water was a gas! Because Earth was
very hot!
Formation of Organic
Molecules
Early atmosphere allowed the
formation of organic molecules
– because it DID NOT have oxygen
– Would not form in today’s atmosphere
Oxygen is too reactive
Bacteria would eat the molecules
Miller and Urey
Stanley Miller and Harold Urey
attempted to answer whether
Organic molecules could have
formed before life was present.
Filled an enclosed flask with
a mixture of gases and water to
simulate the Earth’s Atmosphere!
Used electrodes to produce a
Spark that simulates lightning!
Miller and Urey made
sure no microscopic
life existed in this
experiment. Why?
They had to make sure the original
simple substances they were testing
were the ONLY possible source for the
creation of organic molecules.
The Results from Miller
and Urey
Amino acids began to form after a
couple days.
This mixture of amino acids and other
organic compounds showed us that
molecules necessary for life could
have risen from simple compounds
present on early Earth without life.
The First Cells
Thought to have originated 200-300 million
years after oceans formed.
Why? Because the presences of liquid
water was necessary for first life.
Earliest cells called proteinoid microspheres
were created when organic molecules
became trapped in bubbles
Not alive but have some
characteristics of living cells
They had SELECTIVELY
PERMEABLE MEMBRANES.
Oxygen-Free Life Forms
The first life forms are thought to have
evolved in oxygen free environments
approximately 3.5 billion years ago
First organisms on Earth were most
like today’s BACTERIA
Photosynthetic organisms evolved
in the oceans approximately 2.2 billion
years ago
Started pumping oxygen into the
atmosphere
Endosymbiotic Theory
Belief is that eukaryotes formed approx. 2
billion years ago from COMMUNITIES of
PROKARYOTES.
– Prokaryotes “moved into” prokaryotic cells
Created a symbiotic relationship
– One group was able to use oxygen to make ATP
Mitochondria
– One group was able to use light to make sugars
Chloroplasts
Evidence of the
Endosymbiotic Theory
Membranes of mitochondria and
chloroplasts are similar to that of freeliving prokaryotes
Mitochondria and chloroplasts have
– DNA similar to bacterial DNA
– Ribosomes similar to those of bacteria
– Reproduce by binary fission
Sexual Reproduction
The use of sexual reproduction by
early organisms allowed evolution to
occur at a much quicker rate
– More gene shuffling