Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
History of life notes Early Earth 4.6 bya (billion years after) - VERY (colliding meteorites, erupting volcanoes) - Atmosphere was mostly nitrogen, carbon dioxide, water vapor, methane, ammonia but NO OXYGEN!!!!! 4.4 bya - Earth cools - water vapor condenses into rain creates oceans (where the first life will form) Evidence that we do have! Fossils = evidence of an organism that lived long ago and show the great diversity of life (Examples: A person who studies fossils is called a paleontologist (just like Ross on Friends!) How is a fossil made? - After an organism is buried, the sand and clay around it harden to form sedimentary rock. Then erosion brings the fossil to the surface Dating Fossils 1. Relative Dating- older rocks/fossils are on the bottom, younger ones are on top 2. Absolute Dating (also called radiometric dating)- measures the amount of radioactive substance left in the rock or organism and determines its actual age By examining rock layers and dating the fossils, scientists have been able to put together a chronology, or calendar of Earth’s history called the Geologic Time Scale (see left page) Origin of Life Cell Theory 1. all living things are made of cells 2. cells are basic unit of structure & function 3. All cells come from pre-existing cells. What is the big question this theory raises? 1. Where did the first cell come from? 2. What can be observed now if it happened so long ago? - The initial belief was that life was created through spontaneous generation (abiogenesis). Example: a piece if decaying meat produces maggots (baby flies) Disproving Spontaneous Generation 1. Francesco Redi was the first to disprove spontaneous generation in the 1600s. History of life notes Although Redi was able to disprove that large organisms did not simply appear, many scientists thought that microorganisms (bacteria) were so numerous and widespread that they must arise spontaneously- probably from a vital force in the air. 2. Louis Pasteur in the mid 1800’s designed an experiment that disproved the spontaneous generation of microorganisms From this time on BIOGENESIS, the idea life comes from life holds true. (Ex. Humans give birth to humans, mice to mice, etc.) But…. How did the very first life form that start this chain reaction?!!! The current theory is that life began in the oceans. Oparin’s hypothesis: Energy from the sun and lightning triggered chemical reactions with the vapors that were present in the early atmosphere to produce small, organic molecules. Then, the rain washed the molecules into the ocean to create what is called the primordial soup. (place of the origin of life). PROOF?? 1953- Stanley Miller and Harold Urey tested the hypothesis by simulating the conditions History of life notes of early Earth in a lab. Simple Molecules to Complex molecules? - experiments were done to prove that simple molecules like amino acids when heated without oxygen link up to form proteins (complex molecules) Complex Molecules to Cells? - Sidney Fox showed how amino acid chains will form protocells Evolution of Cells 1st cells = prokaryotic, anaerobic and heterotrophic (does not make own food) 2nd cells = autotrophic prokaryotes (makes own food) 3rd cells = photosynthesizing prokaryotes First organisms were prokaryotes 2 types – Archaebacteria – bacteria that live in harsh environments, and more closely related to early prokaryotes – EubacteriaEndosymbiotic theory Pre-eukaryotic bacteria engulfed another – (similar to mitochondria or chloroplast) History of life notes Eukaryotic organisms formed much __________________ than prokaryotes Summary