Download History of Life on Earth - Field Natural History - Lecture Notes and more Study notes History in PDF only on Docsity! Field Natural History History of Life on Earth I. In the beginning…. A. How did life originate? Nobody knows really, no direct evidence survived. B. What is life? A scenario how life developed at the semi-cellular level. 1. A short chain of events a) abiotic synthesis and aggregation of small organic molecules (water, methane, ammonia, carbon dioxide, carbon monoxide → amino acids, acetic acid, urea, hydrogen cyanide. b) These intermediate molecules joined together to form polymers (proteins and nucleic acids) 2. It starts to look like life when the formation of polymers is combined with 3 fundamental properties that define life as we know it. a. Ability to assimilate energy and grow. b. A level of cellular organization – aggregation of polymers into droplets called protobionts. c. Ability to reproduce themselves 3. However, role of heredity very important. The essence of being alive is the ability to encompass change and to reproduce the results of change permanently. Change does not become evolution unless it is passed on to a new generation. II. How organic molecules were formed. A. RNA (ribonucleic acid) – the first molecule, which directs the assembly of proteins. 1. DNA (deoxyribonucleic acid) directs assembly of RNA. (Original and working copies.) B. How conditions on primitive earth favored synthesis of organic compounds. 3 hypotheses. 1. Lightening in a flask theory. a. Reducing environment – Hydrogen (H2), Methane (CH4), and Ammonia (NH4). No oxygen (O2) b. A catalyst or energy source – Ultra violet (UV) radiation or lightening. 2. Hydrothermal vent process. a. Scientists discover conditions leading to the origin of life exist near thermal vents on ocean floor, thousands of feet below surface, where no sunlight shines. b. Bacteria that utilize hot hydrogen sulfide as a source of chemical energy power community of organisms. 3. Nucleic acids and proteins may have arrived from extraterrestrial sources: comets, meteorites and interstellar dust. III. When did life originate on Earth? A. Origin of earth is dated to approximately 4.5 billion years ago (bya). 1. Need sedimentary rocks to create fossils. Oldest are 3.8 by old. So no earlier evidence of life. 2. Oldest sedimentary rocks have crushed and destroyed any early, soft bodied forms of life. 3. Oldest fossil record - filamentous bacteria which formed domes of sediment- Stromatolites, are 3.5 billion years old. Docsity.com
