Topic 3: The Evolution of Life on Earth

Part of the Evolution of Australian Biota ModuleBiology in Focus, Preliminary CourseGlenda Childrawi and Stephanie Hollis

Life on EarthTopic 4: Urey and Miller DOT POINTDiscuss the significance of the Urey and Miller experiments in the debate on the composition of the primitive atmosphereGather information from secondary sources to describe the experiments of Urey and Miller and use the available evidence to analyse the:Reasons for their experimentsResult of their experimentImportance of their experiment illustrating the nature and practice of scienceContribution to hypotheses about the origin of lifeDiscuss the ways in which developments in scientific knowledge may conflict with the ideas about the origins of life developed by different cultures

IntroductionIn the early 1950s, 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.

amnh.org

Origins of lifeUsing the equipment pictured, Urey and Miller placed water, methane, ammonia and hydrogen into sealed glass tubes and flasks connected by a loop.

Origins of lifeThis 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 lifeOne 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 lifeSparks 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 atmosphereOrigins of lifeAfter 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 lifeThis 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 lifeThe 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.

bio.miami.edu

Recent DebateIts important to consider that this is only one scientific perspective and is theory. Its 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. newscientist.com

Recent DebateThere 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 limestoneThe 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 DebateThere is also geological evidence to which supports an oxygen free primitive Earth atmosphere:Fluvial uranium sand depositsBanded iron formationsPaleosols (ancient soils) suggest very low oxygen levelsMantle chemistry dataRecent DebateAnother 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 Millers experiment.

This means that amino acids and organic compounds may have only been formed in smaller amountskalb.com

Other sources for Organic CompoundsMany 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. wallpapervortex.com

blog.mywonderfulworld.orgOther sources for Organic CompoundsThe 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 (panspermia)meteorlab.com

Other sources for Organic CompoundsIn 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.books.google.com

Other sources for Organic CompoundsIn 2000, some scientists argued that organic compounds could have formed in areas other than the atmosphere, such as hydrothermal vents and volcanic aquifers.pmel.noaa.gov

Other sources for Organic CompoundsEven 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.evolution.berkeley.edu

Other sources for Organic CompoundsThe 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.coolhunting.com

Other sources for Organic CompoundsDevelopments 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.

These changes may conflict with the ideas held by different cultures.hroutsourcingconnection.com

Other sources for Organic CompoundsThe 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.themaplesyrupguys.blogspot.com

isx.org.au

HomeworkStudents to complete DOT Point 1.6 and 1.7