1. History of Life on Earth

2. Ceno- zoic Meso- zoic Humans Paleozoic Colonization of land Animals Origin of solar system and Earth Fig. 25-7 4 1 Proterozoic Archaean Prokaryotes years ago Billions of 3 2 Multicellular eukaryotes Single-celled eukaryotes Atmospheric oxygen

3. Oparinand Haldane hypothesized that the early atmosphere was highly electrical • Stanley Miller and Harold Urey conducted lab experiments that showed that the abiotic(non-living) synthesis of organic molecules in the early atmosphere is possible • They spent years researching and trying to recreate a closed system that mimic what they believed to be the conditions of early Earth.