scientists have determined the composition of the lithosphere and asthenosphere but have struggled to discover much about the lower mantle (mesosphere). what are the compositions of the upper two parts of the mantle? why is it difficult for scientists to learn about the mesosphere? How could they try to gather more information about it?

Cells in the nervous system have a potential difference of 70 mv across the cell membrane separating the interior of the cell from the extracellular fluid. this potential difference is maintained by ion pumps that move charged ions across the membrane. is this an emf? select the correct answer and explanation. 1)no. the ion pumps cannot separate charges; thus, they cannot create a potential difference. 2)yes. the ion pumps cannot separate charges, but they still can create a potential difference. 3)yes. the ion pumps can actively separate charge; thus, they can create a potential difference. 4)no. the ion pumps can separate charges, but they cannot create a potential difference.