1) The brown gummy would be going through a Food & Beverage. The ink pen and note would be going through Chromatography. The white powder would be going through Qualitative analysis.
2) The gummy would be tested for food safety, nutrition, and quality. The ink pen would be tested for separating a mixture of chemical substances into its individual components. The white powder would be tested for a reaction.
3) The method would work for the brown gummy to see why it's brown, how long has it been sitting out, and is there any connection to the case. The method would work for the ink pen and note so it can be thoroughly analyzed to see if it was written in a distressing or frightening matter. The method for white powder would work to determine if it's narcotics or just baking powder.
Without an oxygen atmosphere very few things could live on the early Earth. Anaerobic bacteria were probably the first living things on Earth. The early Earth had no oceans and was frequently hit with meteorites and asteroids.
