Life on Earth POINT 1
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Transcript of Life on Earth POINT 1
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Life on Earth
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1. Analysis of the oldest
sedimentary rocksprovides evidence for
the origin of life
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identify the relationship between the conditions on
early Earth and the origin of organic molecules
The Earth is thought to be approximately 4.5 billion years old
This was during the Hadeon eon
Gaseous cloud was transformed into a solid body
The heavier molten iron sank down to become the core
While the lighter rock rose to the surface and became the crust
The high temperatures at the core and resulting volcanic activity, caused
gas emisions of volatile substances such as water (H2O), methane (CH4),
ammonia (NH3), hydrogen (H2), nitrogen (N2), and carbon dioxide(CO2)
The atmosphere was ANOXIC (no free oxygen O2)
Oxygen was bound up in water and carbon dioxide
There was no ozone layer (O3) and this exposed the surface of the Earth to
UV radiation
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So how did the first organic molecules form?
Early Earth consisted of an atmosphere of water vapour, hydrogen,methane and ammonia all the elemental requirements for making
organic molecules
The main energy for the conversion into organic molecules came from the
sun
UV radiation (as no ozone existed), lightning hot springs, volcanic activityand meteorite impacts could have provided energy too.
Organic chemicals would have likely formed in the lower atmosphere or
Earths surface.
Dense clouds of water vapour would have formed a protective shield from
the suns penetrating heat. Meteorite impacts would have declined due to the protective l;ayer.
Temperatures would have cooled resulting in the condensing of vapour
clouds into liquid water and falling as rain
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Rain would have washed organic molecules into lakes and ponds, creating
new organic molecules.
Carbon dioxide would have dissolved in water forming carbonic acid,
which would have reacted with calcium in the oceans to form calciumcarbonate
Heat dissipated into space and the crust formed by the cooling of the
Earth.
Over the next 3.5 billion years, carbon dioxide content decreased as it was
incorporated in rocks as limestone.
The main remaining gas was nitrogen (78%)
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Discuss the implications of the existence of organic
molecules in the cosmos for the origin of life on Earth
There is little evidence for the existence of organic molecules in the
cosmos
Strong evidence would suggest that the organic molecules that we have
here on Earth had an extraterrestrial origin.
The Murchison meteorite in 1969, provided some evidence that thecosmos has some similarities in the organic molecules found on earth
today.
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Describe two scientific theories relating to the evolution of
the chemicals of life and discuss their significance in
understanding the origin of life
Panspermia
This theory involves the origin of organic molecules coming from thecosmos.
Materials found in meteorites and comets have revealed the presence oforganic molecules which may have acted as seeds falling onto early
earth.Biochemical formation on Earth
Oparin and Haldane suggested that organic compounds could haveformed in the oceans of early Earth from simple inorganic compounds.
The energy for this would have been provided by UV radiation from the
sun. A primoidal soup of organic compounds would have formed in the
oceans.
This theory had no evidence, until Urey and Miller conducted experimentsto show that it was possible to get organic compounds from inorganicones.
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Gather information from secondary sources to describe the
experiments of Urey and Miller and use available evidence
to analyse the:
reason, result, importance and contributions to theorigin of life.
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Reason for their experiments
They endeavoured to show if it was experimentally possible for organic
compounds to be formed from the inorganic compounds thought to be
found on early Earth ie they tried to back up the theory of Haldane andOparin.
The gases present on early Earth (CH4, NH3, H2, H2O) were in a sealed glass
chamber.
An electrical spark was used to create the energy, to simulate lightning
that would have been frequent on early Earth.
Result of their experiments
After a week, the experiment resulted in a solution containing aminoacids, which are vital components in living things.
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Importance of their experiments in illustrating the nature and practice ofscience
Anyone can propose a theory as to how something works, why something
is the way it is or, in this case, how organic molecules formed on Earth. BUT it is the nature and practice of science to test such theories and
hypotheses by conducting experiments
This is what Urey and Miller did. They took the theory of Haldane andOparin, and scientifically tested to see if it was possible to create organicmolecules (amino acids) from the inorganic ones found on early Earth.
They repeated their experiments and they yielded the same result, whichis a key factor in the scientific method.
Contribution to hypotheses about the origin of life
Urey and Miller showed that it was possible to experimentally gat aminoacids, and this gave some credence to the theory that organic moleculesarose on Earth (and not from the cosmos).
It does, however, NOT prove that this is the way that they formed. Itsimply says that it is possible that they did.
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Discuss the significance of the Urey and Miller
experiments of the primitive atmosphere
Urey and Millers experiments provided the first experimental evidence
that it was possible to produce living (organic) substances.
This has been called the chemosynthetic origin of life.
The experiments were replicated to produce a similar outcome.
Some scientists have replicated the experiment, but used UV light insteadof electricity, and still produced amino acids
Another scientist, Oro, produced adenine which is an organic compound
found in DNA and ATP.
Urey and Millers experiments have opened up significant debate as to the
origin of these organic molecules. Debates have centered around the factthat there is some geological evidence to suggest that there was no free
H2, and other evidence suggests there was.
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Identify changes in technology that have assisted in
the development of an increased understanding of
the origin of life and evolution of living things.
Francesco Redi used glass jars and cotton wool to test his theory of
spontaneous generation with flies and meat. This tested the idea that
organisms could originate from non-living matter.
Louis Pasteur disproved spontaneous generation by using his classic swan-
necked flask experiment. Leeuwenhoek and his light microscope allowed the viewing of organisms
not visible with the naked eye.
More recent technologies include the development of the electron
microscope. This led to the understanding of the molecular structure of
living things, the remains of microorganisms and mineral nature of earlyrocks
Radiometric dating has helped determine the geological age of fossils and
surrounding rock material
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Seismology provided knowledge of the structure of the Earth and the of
characteristics earthquakes.
Geology and geophysics used information about the fossil record,
concepts of continental drift and seas floor spreading to establish the ageof the Earth.
The discovery of the absolute age of fossils by looking at the relative
proportions of radioisotopes
X-ray crystallography has been used to determine the structure of various
compounds and molecules such as DNA structure.
Biochemical analysis, amino acid and nucleotide sequencing has allowed
comparisions between ancient material and modern compounds, as well
as comparative studies of different organisms.