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Lecture

EPSC201 Lecture 22 Notes.doc


Department
Earth & Planetary Sciences
Course Code
EPSC 201
Professor
Anthony Williams- Jones

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EPSC 201 Lecture 22 Notes
In the last class we looked at where the
origin of life might have started. Could life
come from other parts of our solar system.
There was a Martial meteorites that may
have contained fossils. There was also
nucleic acids found in the meteorites.
Carbonaceous chondrites have been
found on earth with many different com-
plex molecules. Life may have existed on
Mars, so there are space exploration mis-
sions dedicated to this. Water was present
on Mars, and formed evaporites and
canals.
Miller envisioned an early atmosphere with no oxygen, but rich in ammonia and methane. Light-
ning could have provided the energy to produce amino acids and other complex molecules that
are building blocks of life. He showed that
a closed system with the gases shown
above, when subjected to electricity, can
produce amino acids. This provided some
energy to say that life may have started in
the ocean interface.
There are long strands of DNA in the nucle-
us of the cell. There are four bases, which
comprise genes when ordered the right
way. Different sequences give different
proteins. The backbone of DNA is made
from sugars and phosphorus. The DNA is tran-
scripted into an RNA molecule. The RNA exits the
nucleus, and is translated into a protein by the ribo-
some’s. This occurs in the cytoplasm of the cell.
The RNA is like a book, being read by the ribosome.
The early Earth was almost entirely ocean. Around
2.5 billion years ago, there started to be land on the
surface. In the 1970s we discovered black smok-
ers in mid ocean rideges. There was plenty of thriv-
ing species in these areas, that should have been
too deep to support life. Depths of several kilome-

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ters don’t allow for photosynthesis. So the metabolic pathway then, is much different. It is called
chemosynthesis. The animals used the thermal energy at the spreading centers, hot spots, and
subduction zones (all hot) to synthesis chemicals necessary for life.
Black smokers have the ability to produce com-
plex molecules. There is iron present, which
acts as a catalyst to produce big organic mole-
cules from simple gases, such as carbon
monoxide, oxygen, sulphur, nitrogen, and water.
These building blocks are catalyzed by metallic
iron, or iron sulphide, to make complex mole-
cules.
At a spreading center, we have rift faults. Water
moves downwards into the mantle, and is even-
tually heated up. The water moves back up,
and generates these black smokers. They are
black due to all the precipitates coming out of
the hot water. There is iron sulphide, pyriditite,
and other precipitates. There are lots of iron
complexes and sulphates which make the smoker look black. The water comes out of the smoker
at about 300 degrees, but stays in the liquid form due to the underwater pressure of the ocean.
The mineral olivine is converted into serpentine, magnetite, and hydro-
gen. This hydrogen can be used as a precursor. This reaction takes
place in the mantle. The hydrogen gas will work its way up towards the
surface, where it can take place in the reactions in black smokers. The
mantle also has lots of carbon. There will be nitrogen gas, carbon
monoxide, sulphur gases present in the black smokers. All of the reac-
tants necessary to make the building blocks of life were present.
Olivine -> serpentine + magnetite + hydrogen
An important feature of this structure is an ability to omit metal atoms
with the total fraction up to 1/8, thereby creating iron vacancies. One of
such structures is pyrrhotite-4C (Fe7S8). These irregularities could be
causing the pyrrhotite to act as a template to form specific complex or-
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ganic molecules. We know this mineral is found in black smokers. There is a link between the
geological processes and biological origin.
Life is divided into two basic categories, eukaryotic (EU) and prokaryotic (P). P are mostly single
cells and don’t have a defined nucleus. EU are mostly multicellular organisms that do have a nu-
cleus, and evolved from singled celled organisms.
The prokaryotic life form evolved first, and is much simpler. The EU have more complex cellular
machinery, and much more DNA. There is a defined nucleus in the center of the cell, containing
all the DNA. The prokaryotic cells have less DNA, which is circular in structure and called a plas-
mid.
There is a theory that the eukaryotic cell’s mitochondria was a separate prokaryotic cell, that got
swallowed up by another prokaryotic cell, and formed a symbiotic relationship.
How do cells replicate? The prokaryotic cells undergo fission, where the cell basically splits in
half. This is very straightforward, as it only takes one parent to produce an offspring. There is
less genetic variation between generations, compared to organisms that have two parents.
All early life was prokaryotic. The first EUs occurred around 1.8 billion years ago. This is inter-
preted from fossil representation, but we are essentially positive that the first life forms were
prokaryotic. At 1.8 billion years ago, we have both EU and P. As soon as eukaryotics life came to
be, evolution proceeded much more rapidly. Note how the oxygen is increasing in content as time
progresses forward. Oxygen built up in the atmosphere.
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