The decomposers would be at the very top trophic level. Grass (Producer) is eaten by a mouse (level one consumer) then the mouse is eaten by the snake (level two consumer) then the snake doesn't have enough energy to continue and dies, then leaving the decomposers at the top like fungus to feed off that and return the nutrients to the producers so they can grow.
Answer: Igneous rock forms between sedimentary layers.
This can definitely help in determining relative age because sedimentary rocks will be the older rock than igneous rock as igneous rock has formed between sedimentary rocks