2. layers of epithelial tissue
that serve as barriers to
pathogens and produce
chemical defense

i think that is new experiments yield untrustworthy data and should be carefully considered, because you don't know what will happen with the experiments.

answer:

convection currents in the magma drive plate tectonics. heat generated from the radioactive decay of elements deep in the interior of the earth creates magma (molten rock) in the aesthenosphere. the aesthenosphere (70 ~ 250 km) is part of the mantle, the middle sphere of the earth that extends to 2900 km.