WHERE DID LIFE COME FROM ON EARTH???
Recent Debate:
It’s important to consider that there is more than just one scientific
perspective and theory on the origin of life. Below is a summary of the
debate between the Chemosynthetic origins and Panspermia, more can
be found in your textbook or online if you want further reading.
Urey-Miller version of events – chemosynthetic
origins
After a week, they observed that as much as 1015% of the carbon was in the form of simple
organic compounds, with 2% forming amino
acids. 13 of the 22 amino acids formed were
those used to make proteins in living cells.
Compounds from outer space theory Panspermia
The Murchison Meteorite (and others) found in
1969 in Victoria contained over 90 amino acids,
of which 19 are found on Earth. The primitive
Earth is believed to be similar to many of the
comets and asteroids in our galaxy.
There is some doubt, looking at early geological
history, as to what the atmosphere of early earth
was like. Evidence can be found that perhaps
there was not much free Hydrogen gas (as used
in the Urey-Miller experiment):
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precipitation of lime stone
oxidisation of ferrous rock
distribution of minerals in the early
sedimentary rocks
recent studies on composition of
volcanic gases
Another objection is that these experiments
required a significant amount of energy. It is
argued that although lightning storms were
common on primitive Earth, they did not occur
continuously as portrayed in Urey and Miller’s
experiment. This means that amino acids and
organic compounds may have only been formed
in smaller amounts.
The experiments of Urey and Miller remain
significant in the advancement of ideas
surrounding the composition of the primitive
atmosphere. It was the start of forming some
kind of evidence for how the primitive earth may
have been, and therefore how life began here.
This experiment has led to further experimental
testing and exploration into this area of Science.
Currently there is more evidence supporting
chemosynthesis.
This demonstrates the possibility, but not proof
that Earth may have received organic
compounds and amino acids from outside the
planet (Panspermia).
If amino acids are able to survive the extreme
conditions of outer space then this might suggest
amino acids were present when the Earth was
first formed.
Scientists are always searching the universe for
more evidence to support panspermia.
Other theories:
In 2000, some scientists argued that organic compounds could have formed in areas other than the
atmosphere, such as hydrothermal vents and volcanic aquifers.
Even though we continue to obtain more evidence towards the composition of the atmosphere of
primitive Earth, each piece of evidence may support different theories. Scientists may interpret the
evidence differently and the controversy and debate will continue.
Developments in scientific knowledge about the origins of life are constantly occurring as discoveries
are made and new technologies provide more advanced approaches to unanswered questions.
As scientists, the most probable theory to date is Chemosynthesis… BUT, how do we explain how
these simple amino acids and proteins became the complex beings that exist today. There is much
more work to be done, perhaps as more evidence comes to light
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Identify changes in technology that have assisted in the development of an increased
understanding about the origin of life and the evolution of living things.
Read page 126- 130 of your textbook. Technology Changes and the Origin of Life.
Write a summary of the technology changes and their assistance in understanding the origin of
life.
Resources:
www.astrobiology.nasa.gov; http://prelimbio.wikispaces.com; http://spbbiologylifeonearth.wikispaces.com; https://www.geology.ucdavis.edu
http://phys.org/news/2011-10-astronomers-complex-universe.html
Images from: http://www.fanpop.com; http://www.daviddarling.info
and table from Biology in Context.
Astronomers discover complex organic matter in the
universe
October 26, 2011
This is a spectrum from the Infrared Space Observatory
superimposed on an image of the Orion Nebula where these
complex organics are found. Credit: NASA, C.R. O'Dell and
S.K. Wong (Rice University)
In today's issue of the journal Nature, astronomers
report that organic compounds of unexpected
complexity exist throughout the Universe. The results
suggest that complex organic compounds are not the sole
domain of life but can be made naturally by stars.
Prof. Sun Kwok and Dr. Yong Zhang of the University of Hong Kong show that an organic
substance commonly found throughout the Universe contains a mixture of aromatic (ringlike) and aliphatic (chain-like) components. The compounds are so complex that their
chemical structures resemble those of coal and petroleum. Since coal and oil are remnants of
ancient life, this type of organic matter was thought to arise only from living organisms. The
team's discovery suggests that complex organic compounds can be synthesized in space even
when no life forms are present.
The researchers investigated an unsolved phenomenon: a set of infrared emissions detected in
stars, interstellar space, and galaxies. These spectral signatures are known as "Unidentified
Infrared Emission features". For over two decades, the most commonly accepted theory on
the origin of these signatures has been that they come from simple organic molecules made of
carbon and hydrogen atoms, called polycyclic aromatic hydrocarbon (PAH) molecules. From
observations taken by the Infrared Space Observatory and the Spitzer Space Telescope,
Kwok and Zhang showed that the astronomical spectra have features that cannot be explained
by PAH molecules. Instead, the team proposes that the substances generating these infrared
emissions have chemical structures that are much more complex. By analyzing spectra of star
dust formed in exploding stars called novae, they show that stars are making these complex
organic compounds on extremely short time scales of weeks.
Not only are stars producing this complex organic matter, they are also ejecting it into the
general interstellar space, the region between stars. The work supports an earlier idea
proposed by Kwok that old stars are molecular factories capable of manufacturing organic
compounds. "Our work has shown that stars have no problem making complex organic
compounds under near-vacuum conditions," says Kwok. "Theoretically, this is impossible,
but observationally we can see it happening."
Most interestingly, this organic star dust is similar in structure to complex organic
compounds found in meteorites. Since meteorites are remnants of the early Solar System, the
findings raise the possibility that stars enriched the early Solar System with organic
compounds. The early Earth was subjected to severe bombardments by comets and asteroids,
which potentially could have carried organic star dust. Whether these delivered organic
compounds played any role in the development of life on Earth remains an open question.