8.4 Life On Earth
Students Learn About
1. Analysis of the oldest
sedimentary rocks provides
evidence for the origin of life
• Identify the relationship
between the conditions on early
Earth and the origin of organic
THE AGE OF THE EARTH
- based on geological, magnetic, radiographic and paleontological studies: aged 4.5 billion years
- Hadean eon: formation of earth from gaseous cloud to solid body. Heavy molten iron sank down and became the core, lighter rock came to surface = crust - As a result of the high temperatures at the centre of the Earth and due to volcanic activity, there as an emission of gases, or out-gassing, of volatile molecules, such as water (H2O), methane (CH4), ammonia (NH3), hydrogen (H2), nitrogen (N2), and carbon dioxide (CO2).
- Environment was anoxic (no free oxygen) = no ozone layer, earth exposed to high solar radiation (UV)
- Early Earth = atmosphere of water vapour, hydrogen, methane and ammonia making production of organic carbon-containing easier.
- energy for driving these reactions could have come from a number of sources, in particular the sun. Ultraviolet light would easily have reached the Earth’s surface because no ozone layer existed. Other sources include: lightning, hot springs and volcanoes, radioactivity in the crust, and impact from meteorites.
- Organic molecules most likely formed in lower atmosphere or earth’s surface STAGES OF EARTH’S DEVELOPMENT
- Dense clouds of water formed in the atmosphere, which reflects the sun’s heat - Earth cooled sufficiently to allow for the formation of a rocky crust. - Volcanic gas eruptions increased the air pressure, forming clouds which allowed for the water vapour to condense and fall as rain.
- Water would have absorbed a lot of the carbon dioxide present in the atmosphere due to solubility.
- The cooling process by the rain continued until the Earth was cool enough to allow for the formation of rivers and oceans.
- Heat was dissipated into space, causing a more solid crust to form - From then on, the process of reducing the amount of carbon dioxide was occurring – EXAMPLE: transferring it into rocks like limestone.
• Discuss the implications of the
existence of organic molecules
in the cosmos for the origin of
life on Earth
- little evidence of organic molecules existing in universe or cosmos - Meteorites: contain organic molecules similar to Earth’s - suggests origin of organic molecules on Earth may have come from outside Earth - Urey and Miller replicated conditions of early Earth in order to show that organic molecules can be formed from inorganic reactants. This theory is commonly supported, however, there is no evidence to show the transformation of organic molecules into life.
• Describe two scientific theories
relating to the evolution of the
chemicals of life and discuss
their significance in
understanding the origin of life
- proposed by Aristotle
- suggested life arose spontaneously from particles that contained “active principle” - Correctly stated that fertile egg contained “active principle” but also stated that meat, mud and wood contained the same element.
- Disproven by Louis Pasteur
- Significance: assisted us in understanding that is it extremely unlikely that life simply generated from its non-living substances
Students Learn About
- suggests that life could have arisen once, or several times, at various times and in various parts of the universe
- Materials found in meteorites and comets may have acted as ‘seeds’ falling onto the Earth
- no evidence to support / disprove this theory due to lack of ability to explore space but the similarity of amino acids in meteorites and Earth do provide some inclination towards Panspermia
- Significance: understanding of the origin of life as it opens the option of life may be existent outside the Earth – a hypothesis that will never be proven wrong BIOCHEMICAL EVOLUTION...
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