BIOL1402 Chapter 15 Lecture

BIOL1402 Chapter 15 Lecture - 1 Chapter 15 Tracing...

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1 Chapter 15 Chapter 15 Tracing Evolutionary History 2 Introduction ± Different types of wings evolved from the same ancestral tetrapod limb. – Pterosaur wings consist of a membrane primarily supported by one greatly elongated finger. – Bird wings consist of feathers supported by an elongated forearm and modified wrist and hand bones. – Bat wings consist of a membrane supported by arm bones and four very elongated fingers. 3 4 5 EARLY EARTH AND THE ORIGIN OF LIFE 6 15.1 Conditions on early Earth made the origin of life possible ± The Earth formed about 4.6 billion years ago. ± As the Earth cooled and the bombardment slowed about 3.9 billion years ago, the conditions on the planet were extremely different from those today. – The first atmosphere was probably thick with – water vapor and – various compounds released by volcanic eruptions, including nitrogen and its oxides, carbon dioxide, methane, ammonia, hydrogen, and hydrogen sulfide. – Lightning, volcanic activity, and ultraviolet radiation were much more intense than today. 7 15.1 Conditions on early Earth made the origin of life possible ± The earliest evidence for life on Earth – comes from 3.5-billion-year-old fossils of stromatolites , – built by ancient photosynthetic prokaryotes still alive today. ± Because these 3.5-billion-year-old prokaryotes used photosynthesis, it suggests that life first evolved earlier, perhaps as much as 3.9 billion years ago. 8 9 15.1 Conditions on early Earth made the origin of life possible ± The first life may have evolved through four stages. 1. The abiotic (nonliving) synthesis of small organic molecules, such as amino acids and nitrogenous bases. 2. The joining of these small molecules into polymers, such as proteins and nucleic acids. 3. The packaging of these molecules into “protocells,” droplets with membranes that maintained an internal chemistry different from that of their surroundings. 4. The origin of self-replicating molecules that eventually made inheritance possible. 10 15.2 SCIENTIFIC DISCOVERY: Experiments show that the abiotic synthesis of organic molecules is possible ± In the 1920s, two scientists, the Russian A. I. Oparin and the British J. B. S. Haldane, independently proposed that organic molecules could have formed on the early Earth. ± Our modern atmosphere is rich in O 2 , which oxidizes and disrupts chemical bonds. ± The early Earth likely had a reducing atmosphere. 11 15.2 SCIENTIFIC DISCOVERY: Experiments show that the abiotic synthesis of organic molecules is possible
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± In 1953, graduate student Stanley Miller, working under Harold Urey, tested the Oparin- Haldane hypothesis. – Miller set up an airtight apparatus with gases circulating past an electrical discharge, to simulate conditions on the early Earth. – He also set up a control with no electrical discharge.
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BIOL1402 Chapter 15 Lecture - 1 Chapter 15 Tracing...

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