Lecture 6

Lecture 6 - e Origin and Evolutio of Life on Earth Summary...

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Unformatted text preview: e Origin and Evolutio of Life on Earth Summary so far… Chapter 4 – The habitability of Earth : How and why Earth has remained a suitable home for life over the > 4 billion years of it’s life. Qu : How did life arise in the first place? Qu : What events have shaped life’s evolution into its current diversity? Chapter 5 – Evolution : Allowing life to take advantage of the habitability of Earth, with natural selection leading to the great diversity of life we see today. How life exists in almost every corner of the planet that has even the smallest amount of water. When did Life Begin? The geological record details much of the history of life on earth. The theory of evolution details how life has changed from the earliest life until now. Neither can tell us how and precisely when life first arose on Earth! Occurrence of life on Earth – fossils! Find a fossil of a certain age – we know that life already existed at that time. Stromatolites Stromatolites – “rock beds” characterised by a distinctive layered structure. Ancient stromatolites look virtually identical to modern ones (living stromatolites). 1.Layers of sediment intermixed with different types of microbes. 2.Microbes at the top generate energy through photosynthesis – those beneath use organic compounds left as waste products by the photosynthetic microbes. 3.Living stromatolites grow as sediments are deposited over them, forcing the microbes to migrate upward in order to remain at the depths to which they are adapted –creates layers! • Contain chemical and isotopic evidence of a biological origin. • Microbial colonies 3.5 Ga years ago? • Photosynthetic microbes? A sophisticated process – taken a while to evolve! • More primitive life existed earlier? Microfossils Ancient microscopic fossils – rare, affected by geological processes, hard to recognise as biological. Oldest claimed microfossils : 1) 3.5 Ga old, NW Australia, Pilbara Greenstone Belt. • Structures of individual cells and organic carbon. • Assumed to be within sedimentary rock from a shallow sea – fossils of early photosynthetic organisms? Actually from near a deep-sea volcanic vent - so the organisms could not be photosynthetic – not fossils? 2) 3.5 – 3.2 Ga old, Southern Africa, Barberton. • Fossil cells. • Appear to share similar origins to Pilbara cells....
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This note was uploaded on 03/08/2011 for the course ASTRO 2021 taught by Professor Brown during the Spring '10 term at UWO.

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Lecture 6 - e Origin and Evolutio of Life on Earth Summary...

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