19.1 How Did Life Begin? I. Bacteria were the first to evolve A. 3.5 billion year old bacterial fossils have been found 1. Prokaryotic – no internal compartments B. Cyanobacteria 1. Photosynthesis – releases oxygen into atmosphere a. took millions and millions of years but today 21% of atmosphere is oxygen C. Maybe the ancestors of chloroplasts and/or mitochondria

II. Two kingdoms of bacteria A. Eubacteria – cause disease and decay B. Archaebacteria – can produce energy without oxygen (combine hydrogen with carbon dioxide = methane) 1. Most likely the ancestor of all modern eukaryotic cells III. Dawn of the eukaryotes A. Over 1 billion yrs. bacteria were the only living things on earth B. About 1.5 billion years ago 1st eukaryotes appear C. Protists – 1st eukaryotes, had membrane bound nucleus 1. Some were photosynthetic while others hunted bacteria

IV. Multicellular evolution A. First fossil of multicellular organism 630 million yrs. old B. Multicellular protists evolved into 3 different kingdoms 1. fungi, plants, animals V. Cambrian Period – 600 mya to 500 mya A. All major groups, except plants, originated during this time B. Life was more diverse in the seas than it has ever been since

VI. Mass Extinctions A. About 440 mya the 1st of 5 major mass extinctions occurred 1. 360 mya 2nd 2. 250 mya 3rd (96% of all species extinct) 3. 200 mya 4th 4. 65 mya 5th (2/3 of all land species extinct including dinosaurs extinct) B. Another mass extinction may be on the way