Topic 3: The Evolution of Life on Earth

Life on Earth
Topic 4: Urey and Miller
Part of the Evolution of Australian Biota Module
Biology in Focus, Preliminary Course
Glenda Childrawi and Stephanie Hollis
 Discuss the significance of the Urey and Miller experiments
in the debate on the composition of the primitive atmosphere
 Gather information from secondary sources to describe the
experiments of Urey and Miller and use the available
evidence to analyse the:
 Reasons for their experiments
 Result of their experiment
 Importance of their experiment illustrating the nature and
practice of science
 Contribution to hypotheses about the origin of life
 Discuss the ways in which developments in scientific
knowledge may conflict with the ideas about the origins of
life developed by different cultures
In the early 1950’s, Harold
Urey and his student Stanley
Miller carried out the first
experiment simulating
hypothetical conditions
present on Earth 4 billion
years ago in order to look at
the chemical reactions that
may have occurred.
Origins of life
Using the equipment
pictured, Urey and Miller
placed water, methane,
ammonia and hydrogen
into sealed glass tubes and
flasks connected by a loop.
Origins of life
This apparatus was a
simulation in which water
and gases (representing the
Earths early oceans and
atmospheres) could be
heated and circulated
through sparks which
simulated lightning.
Origins of life
One flask was half filled with
liquid water and the other
contained a pair of
electrodes. The water was
heated to cause it to
evaporate into steam.
Origins of life
Sparks were created between
the electrodes in the other
flask to simulate lightning
storms in a steamy
atmosphere. The steam
cooled and condensed back
into liquid trickling back into
the first flask, simulating an
atmosphere that was cooled.
This was continuously
repeated simulating a cycle in
the early atmosphere
Origins of life
After a week, they observed
that as much as 10-15% 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!
Origins of life
This experiment provided the first experimental evidence that
it is possible for inorganic substances to produce living
(organic) substances. This theory has been called the theory
of biochemical evolution.
Origins of life
The experiments have been
replicated successfully to
provide a similar
outcome each time.
Some scientists have
replicated this
experiment using
ultraviolet light instead of
electricity to produce
nitrogen bases and
nucleotides as well as
amino acids.
Recent Debate
It’s important to consider
that this is only one
scientific perspective and is
theory. It’s not proven to
create life, and this
experiment is currently
under investigation as we
are not exactly sure what
the atmospheric conditions
were 4 billion years ago.
Recent Debate
There has been recent doubt concerning this experiment as it is
now believed that the atmosphere of early Earth did not
contain free hydrogen. There is geological evidence which
supports this:
 In the precipitation of limestone
 The oxidisation of ferrous iron in early rocks
 The distribution of minerals in early sedimentary rocks
 Recent study of the composition of volcanic gases
 Recent study of the destruction of molecules by UV radiation
Recent Debate
There is also geological evidence to which supports an oxygen
free primitive Earth atmosphere:
 Fluvial uranium sand deposits
 Banded iron formations
 Paleosols (ancient soils) suggest very low oxygen levels
 Mantle chemistry data
Recent Debate
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
This means that amino acids and organic compounds may have
only been formed in smaller amounts
Other sources for Organic Compounds
Many of the organic compounds made in the Urey and Miller
experiments are now known to exist in outer space. There
are other sources of ‘organic ‘building blocks of life’, such as
meteorites, comets and hydrothermal vents.
Other sources for Organic Compounds
The Murchison meteorite found in Victoria in 1969 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 found in our galaxy.
This demonstrates that Earth may have received organic
compounds and amino acids from outside the planet
Other sources for Organic Compounds
In 1997, Douglas C. B. Whittet published an article in the
Astrophysical Journal on the conditions favourable to the
formation of organic compounds that exist in interstellar
dust clouds.
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.
Other sources for Organic Compounds
In 2000, some scientists argued that organic compounds
could have formed in areas other than the atmosphere, such
as hydrothermal vents and volcanic aquifers.
Other sources for Organic Compounds
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.
Other sources for Organic Compounds
The experiments of Urey and Miller remain significant in the
advancement of ideas surrounding the composition of the
primitive atmosphere. This has led to further experimental
testing and exploration into this area of Science.
Other sources for Organic Compounds
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
These changes may conflict with the ideas held by different
Other sources for Organic Compounds
The difference between science and religion has been the basis
of conflict for a long time. We must consider the beliefs of the
individuals and carefully balance culture, religion and science.
This balance may be achieved by recognising the distinctions
between each group and understanding what each one means.
Students to complete DOT Point 1.6 and 1.7

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