A scientist finds a 200 gram rock composed of 150 grams of Lead-207 and 50 grams of Uranium-235. They know that the rock used to be entirely made of Uranium-235. The half-life of U-235 is 700 million years. How old is the rock?

This is a typical grassland food web. it is also a small picture of an important cycle on earth: the carbon cycle. describe how the carbon gets into this food web. a) bacteria and fungi, the decomposers, recycle carbon from dead organisms. b) carbon is found in the grass and is passed from one level to the next in this food web. eliminate c) all living things give off carbon dioxide as a by-product of respiration and it is released into the atmosphere. d) plants use carbon dioxide as a reactant in photosynthesis, to make usable chemical energy in the form of a sugar.