Early Atmosphere Little or no oxygen Composed of: Carbon Dioxide Water Vapor Nitrogen

Organic Molecules All living things are made from organic molecules, so the presence of these molecules is required for life to exist. Scientists wanted to prove that organic molecules could assemble under conditions of the early Earth.

Miller-Urey Experiment In the 1950's, biochemists Stanley Miller and Harold Urey, conducted an experiment which demonstrated that several organic compounds could be formed spontaneously by simulating the conditions of Earth's early atmosphere. https://www.youtube.com/w atch?v=NNijmxsKGbc

Miller-Urey Experiment Evidence now suggests that the composition of Earth’s early atmosphere was different from their 1953 experiment. However, more experiments with different mixtures of gases have produced similar results.

RNA + DNA Cells are controlled by information stored in DNA, which is transcribed into RNA then translated into proteins. Experiments suggest that small sequences of RNA could have formed from simpler molecules. The “RNA world” hypothesis suggests that RNA existed by itself before DNA. From this simple RNA-based system, several steps could have led to DNA-directed protein synthesis. https://www.youtube.com/watch?v=K1xnYFCZ9Yg

Oxygen Photosynthetic bacteria became common and started to accumulate oxygen in the atmosphere. The ozone layer formed and the sky turned blue. Early life forms who had evolved in the absence of oxygen became extinct.

Endosymbiotic Theory The prokaryotes were the ancestors of eukaryotic organisms. Prokaryotic cells entered ancestral eukaryotic cells and began living inside of them. The endosymbiotic theory proposes that a symbiotic relationship evolved over time, between primitive eukaryotic cells and the prokaryotic cells within them.

Evidence Mitochondria and chloroplasts contain DNA similar to bacterial DNA. They have ribosomes whose size and structure closely resemble those of bacteria. They reproduce by binary fission while cells divide by mitosis.

Endosymbiosis SIMPLE: https://www.youtube.com/watch?v=EQFgT-LUbAQ MEDIUM: https://www.youtube.com/watch?v=9i7kAt97XYU DETAILED: https://www.youtube.com/watch?v=-FQmAnmLZtE