All but one factor is believed to be the source of earth's internal heat energy. that is

Radiogenic heat produced by the Radioactive decay is believed to be one of the source of Earth's internal heat energy.

The Earth is a unique planet. There are two sources of earth's heat--  Radiogenic heat produced by the Radioactive decay and the primordial heat left over from the formation of the Earth. The decay of radioactive elements like uranium inside the earth produces intense heat.

answer: the blood-brain barrier is a layer of specialized membranes and cell processes designed to keep undesirable substances from passing from the bloodstream into the precious tissues of the brain. while the blood-brain barrier does keep most bad things out of the central nervous system, it is not impermeable.

explanation:

the scientific method.