Origins of Life PDF
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This document presents a history of life on Earth, covering key milestones such as the emergence of life, photosynthesis, the evolution of prokaryotic and eukaryotic cells, and the development of organisms like archaea and cyanobacteria. It discusses various theories on the origin of life.
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19.3 Origins of Life Has the Earth changed over time? https://www.youtube.com/watch? v=fdPKlrdUC0w History of Life on Earth 3.5 Billion years ago – First evidence of life 2.7 Billion years ago – Evidence of photosynthesis, Oxygen levels rise 2.1 Billion years ago – First Eukaryote...
19.3 Origins of Life Has the Earth changed over time? https://www.youtube.com/watch? v=fdPKlrdUC0w History of Life on Earth 3.5 Billion years ago – First evidence of life 2.7 Billion years ago – Evidence of photosynthesis, Oxygen levels rise 2.1 Billion years ago – First Eukaryote 1.5 Billion years ago – First multi-cellular Eukaryote 500 million years ago – Colonization of land Abiogenesis The spontaneous generation of life from non- living matter. In the middle ages - It was widely held that maggots arose spontaneously in rotting meat. However, observations made scientists ask questions…. Where do maggots come from? Francesco Redi (Italian 1668) One of the first to disprove spontaneous generation. An Italian doctor who proved maggots came from flies. Lazzaro Spallanzani Some scientists believed that there was a life force in the air Tried to disprove the life force theory Unsuccessful There are microorganisms in the air Louis Pasteur Successful in proving there was no life force Thecurved neck allowed air to pass but trapped microorganisms Biogenesis Allliving things arise from other living things But how did life first form? Oparin (1930) Spontaneous generation did occur once at the beginning of life Believed that at high temperatures and with electrical charge the early gases (water vapor, hydrogen gas, methane, ammonia) could combine to form simple organic compounds As the Earth cooled the organic compounds collected in the oceans = Primordial soup The mysteries of Life’s Origins Earth’s early atmosphere contained little or no oxygen – primarily it was composed of carbon dioxide, water vapor, and nitrogen Stanley Miller and Harold Urey – developed an experiment which replicated the early earth’s atmosphere Miller & Urey (1953) Tested Oparin’s Hypothesis under laboratory conditions and produced some amino acids and sugars Scientistssince then have produced various amino acids, nucleotides, and ATP Alternative Theory Meteorites may have brought organic compounds (amino acids) to Earth RNA Theory (Origins of Heredity) The first molecules of life are hypothesized to have contained RNA Hypothetically RNA Carries genetic information Can be replicated Can make proteins Can behave like protein enzymes and catalyze chemical reactions Hypothesized that RNA evolved into DNA Still unclear how RNA molecules evolved into cellular life. First Cells They were: Prokaryotic (fossil record indicates 3.5 billion years) Anaerobic Heterotrophic A growing population of heterotrophs that depended on spontaneously formed organic molecules for food caused environmental pressure for autotrophs to evolve. First Cells continued… The first autotrophs were similar to present archaebacteria. First autotrophs probably used chemosynthesis to make food The first photosynthetic cells increased in number as the oxygen levels on Earth increased. The fossil record shows a large increase in the diversity of prokaryotes about 2.8 billion years ago. Development of Organisms Anerobic Prokaryotes Photosynthetic Prokaryotes - Cyanobacteria that begins in the oceans (Photosynthesis Unicellular Eukaryotes Multicellular Eukaryotes Endosymbiotic Theory Lynn Margulis Evolution of eukaryotic cells Eukaryotic cells evolved from large prokaryotic cells that were invaded by small aerobic and small photosynthetic prokaryotes Evidence for Endosymbiosis Chloroplasts and mitochondria have their own DNA This DNA closely resembles prokaryotic DNA Mitochondria and chloroplasts can reproduce even when the cell is not These organelles have double membranes One from symbiont One from host May have been taken up by phagocytosis Sexual Reproduction Sometime after eukaryotic cells arose, they began to reproduce sexually Sexual reproduction speeds up evolutionary change because it increases genetic variation
