What is the superposition of strata theory?
1. that oldest layers of sediment in rock formations are found under more recent layers
2. that sedimentary rock is composed of bits of rock eroded minerals
3. that the Earth's is composed of a core, mantle, and crust
4. that rock strata has been laid down for 4.6 billion years

All individuals have two alleles for a given trait. according to mendel's these alleles are passed down one each from both mother and father.

Which is an advantage of having memory cells when a pathogen is encountered for a second time. a) the memory cells are what proliferate into clones of cells in response to the binding of an antigen. b) memory cells are vital to the primary immune response in that they immediately recognize pathogens even at the first encounter. c) memory cells are essentially effector cells that are short lived and attack antigens even without having a receptor specific to that antigen. d) it ensures that more lymphocytes with a receptor specific to a particular antigen will be present than in a host that had never encountered that pathogen.

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