Discuss why scientists know so little about precambrian earth

Consider the model of the oxygen cycle on earth. the majority of earth's oxygen reservoirs are found in the a) atmosphere. b) biosphere. c) hydrosphere. d) lithosphere.

Which is not a likely outcome after extensive irrigation of dry farmland? useless, unproductive soil salinization of the soil depletion of groundwater nutrient-rich soil

Which worm has eyespots that are used to detect light? a fluke b marine worm c planarian d tapeworm