Transcript Origin of the earth

Origin of the earth
 Big bang happened 14
billion years ago.
 Earth and
Moon formed 4.5 billion
years ago (4.5 X 109 )
 Oldest rock is 3.9 billion
years old
• No rock on earth is as old
as the earth itself!
 Oldest fossils are 3.8
billion years old
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Origin of the earth
 The Sun and the planets
are formed from a cloud of
cosmic dust and gas.
 As the earth condensed, a
stratification of its
components took place.
 Heavier materials, moved
into the center while
lighter concentrated near
the surface.
 A crust formed, floating on
the hot molten interior.
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The early atmosphere
 It is thought to have
been principally
composed of:
•
•
•
•
•
N2
Co2
CO
H2O
H2
 Also thought to have
been present:
• H2S
• CH4
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The early atmosphere
 The early atmosphere
is said to be a reducing
atmosphere
• because it is thought to
have contained much
hydrogen which easily
donates electrons
(reduction).
 In a reducing
environment it takes
little energy to form
carbon rich molecules.
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The early atmosphere
What gas is
conspicuously
absent in the early
atmosphere?
When and by what
means did this
gas become 1/5 of
today's
atmosphere?
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The early oceans
 The early oceans are
thought to have been
formed when the earth
cooled and the gaseous
H2O fell in torrential rains
on the crust.
 They must have had
dissolved salts and
minerals from the land
around them and dissolved
gasses from the
atmosphere.
 And soon organic materials
were added.
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The Miller - Urey
experiment
 They tested a theory first
put forward by the
Russian Alexandr Oparin.
 They tested whether it was
possible to get organic
compounds in an
experiment that re-created
the conditions around the
early earth.
 They succeeded in getting
organic gasses and
simple organic acids and
amino acids in solution.
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The origin of life
 Divide into 5 groups
 Each group explores
one possible theory on
the origin of life
• 1. Special/divine creation
• 2. Spontaneous creation
• 3. Panspermia, arrival of
material from outer
space.
• 4. Primitive soup, abiotic
replication of RNA.
• 5. Steady state.
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Clay as a catalyst
 Aharon Katchalsky
(worked in Israel) found
that certain types of
clay could catalyse the
formation of
polypeptides from
amino acids.
• This supported the ideas
that life did need
something like a clay
catalyst at the beginning
because the oceans were
too diluted.
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The Cairns-Smith´s
theory (or clay creation)
 First “organisms” were
made of minerals.
 Basic material is silica
acid, Si(OH)4, in clay.
• It easily polymerises
• not uniform, can be
straight or branching
(with occasional minerals
Mg+2, Al+3, Fe+2)
• diverse infrastructure
• crystal genes were
formed
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The hen or the egg?
 “DNA makes RNA
makes Protein”
 What was the first
molecule that could
replicate itself?
 Which of these three
takes part in all the
processes?
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The RNA world
 Ribose is more easily
synthesised than
deoxyribose.
 RNA can act as a
catalyst.
 RNA can catalyse a
complimentary strand of
itself.
• a 52 nucleotide stretch of
RNA can replicate itself
 but RNA is not stable.
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Coacervate droplets
(the basis of the first cells?)
 Small spherical bubbles
made of a bi-layered
membrane.
 Capable of
• absorbing substances from
the surrounding solution
• facilitated chemical reactions
• exporting products.
 Grow by accumulating subunit molecules from
surroundings.
 Divide by pinching, form
buds.
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Earliest cells
 Fossils of Prokaryotes
from around 3.8 billion
years ago represent the
earliest life forms known
on earth.
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Endosymbiotic theory
Lynn Margulis (USA)
 prokaryotes have been
incorporated into the
eukaryotic cell.
 This theory explains f.ex.
why mitochondria and
chloroplasts :
• have a double membrane.
• have their own DNA, a ring
like prokaryotes
• have smaller ribosomes
• have enzymes on their inner
membrane related to
prokaryotic enzymes
• divide by splitting in two
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Endosymbiotic theory
Lynn Margulis (USA)
 This also means that it is
from prokaryotes that the
four eukaryotic kingdoms
arise.
K. Fungi
K. Plants K. Animals
K. Protists
K. Prokaryotes
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