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History of Life Chapter 14 Biogenesis All living things come from other living things Spontaneous generation • The idea that living things could also arise from nonliving things. Francesco Redi • His experiments showed that maggots came from flies • One open jar and one closed jar • Meat had maggots in the open jar but not the closed jar Lazzaro Spallanzani • His experiments showed that microorganisms are in the air around us. • Boiled broth in two flasks – covered one and left the other open – microorganisms appeared in the open flask Louis Pasteur • His experiments helped to prove biogenesis and get rid of the idea of spontaneous generation. • Used curved neck flasks and broth EARTH’S HISTORY The Formation of Earth • The estimated age of earth is about 4 billion years old. This was determined by studying the many layers of earth surface. Radiometric dating • Method for determining the age of materials Isotopes • Atoms of the same element that differ in the number of neutrons they contain. Most elements have several isotopes. • Mass number of an isotope is the total number of protons and neutrons in the nucleus • Isotopes are designated by their chemical name followed by their mass number. – Example: carbon exists as both carbon-12 and carbon-14 Radioactive decay – • the nuclei of an isotope release particles or radiant energy, or both, until the nuclei become stable. Such isotopes are called radioactive isotopes. Half-life – the length of time it takes for one-half of any size sample of an isotope to decay to a stable form. Alexander Oparin and John Haldane Hypothesized about how the first organic compounds were assembled from earth’s early atomosphere Stanley Miller and Harold Urey • Used Oparin’s hypothesis to set up an experiment and synthesize organic compounds including amino acids in the lab Sidney Fox • Research on physical structures that may have given rise to the first cells • Cell like structures form spontaneously in the lab from solutions of simple organic chemicals • Microspheres – spherical in shape and are composed of many protein molecules that are organized as a membrane • Coacervates – collections of droplets that are composed of molecules of different types, including lipids, amino acids, and sugars • These studies suggest that the gap between the nonliving chemical compounds and cellular life may not be quite as wide as previously thought • However, microspheres and coacervates do not have all of the properties of life. THE FIRST LIFE FORMS The First Cells The first cells were probably anaerobic, heterotrophic prokaryotes The First Cells • Archaea – related group of unicellular organisms, many of which thrive under extremely harsh environmental conditions • Many species of archaea are autotrophs that obtain energy by chemosynthesis instead of photosynthesis The First Cells • Some forms of life had become photosynthetic by 3 billion years ago • Oxygen is a byproduct of photosynthesis • Ozone formed in the upper atmosphere to help protect the earth from ultraviolet radiation The First Eukaryotes • Endosymbiosis – about 1.5 to 2 billions years ago, a type of small aerobic prokaryote was engulfed by and began to live and reproduce inside a larger, anaerobic prokaryote. • The eukaryotes provided a beneficial environment, and the prokaryotes provided a method of energy synthesis.