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Noadswood Science, 2011 Life On Earth To describe how life on Earth began Monday, March 28, 2016 Life How is it that life on Earth began? Life Theories Some religions discuss the theory of creation. They believe the world and all the living things on Earth were created by a supernatural or divine being at a particular time in the past The story is told in the book of Genesis in the Old Testament of the Bible. This theory of creation is believed by Jewish and Christian people who take the Bible literally Other religions have their own beliefs about creation – the Muslim creation story is similar in many ways to the Old Testament with Nabi Adam and Stina Houwa replacing Adam and Eve in the Garden of Eden Life Theories In traditional African cultures, there are various beliefs about the origin of life – some peoples believe that humans originated from a cave in the Earth. Other peoples believe that humans originated from elements in nature, such as reeds in water The cosmozoan theory states that life originated from outer space – the ancient Greeks, Chinese and Egyptians believed that life arose many times out of non-living matter (known as the spontaneous generation theory) Another theory, the steady state theory, is that the Earth has no origin and that it has always been able to support life which has remained unchanged throughout time (this theory has largely been disproved) Early Earth The early Earth was very different to the one we know today – it was hotter and the atmosphere consisted mostly of carbon dioxide, with other gases such as ammonia and methane There are two possible origins for these molecules: They were produced by the conditions on Earth at the time, or They came from somewhere else, such as another planet in our solar system or further out in space Early Earth Over many millions of years these molecules joined with other molecules, becoming gradually more complex and dependent on each other The process of evolution by natural selection eventually led to all of the different living things that we see on Earth today Life Sometime between about 4.1 billion years ago when the Earth’s crust began to solidify, and 3.5 billion years ago life began Most biologists subscribe to the hypothesis that life developed on Earth from non-living materials that became ordered into molecular aggregates These eventually became capable to self-replication and metabolism In the ancient environment the origin of life was evidently possible (conditions were very different, with more intense lightning; volcanic activity; meteorite bombardment; and UV radiation) First Life One hypothesis suggests the first organisms were products of a chemical evolution in four stages: 1. The abiotic (non-living) synthesis and accumulation of small organic monomers such as amino acids and nucleotides from a primordial soup 2. The joining of these monomers into polymers (including proteins and nucleic acids) 3. The aggregation of abiotically produced molecules into droplets (protobionts) with chemical characteristics different from their surroundings 4. The origin of heredity Evidence It is not possible to be certain how life on Earth began because: Earth is about 4,500 million years old There is evidence living things existed on Earth at least 3,500 million years ago No-one was there to record how life began The best we can do is study simple organisms and the chemistry of living things to work out scientific theories The main theory is that living things developed from molecules that could copy themselves, rather as DNA does Miller Urey Experiment It is not known how life began on the Earth because there is not enough evidence available An experiment by Miller and Urey in 1952 tried to recreate the conditions which may have been present in the Earth’s atmosphere around 3 billion years ago… They used a sealed and sterile glass flask with the gases ammonia, methane, hydrogen and water vapour inside – they then passed electrical sparks (simulating lightning) through the gases for a week… Miller Urey Experiment When they analysed the mixture they found many carbon compounds had formed inside the flask (from the methane gas) Some of these compounds were found to be amino acids (used to make proteins) This suggests the first life forms may have been bacteria able to utilise the methane and ammonia to live