Differentiation occurs in what types of cells?
nerve cells
muscle cells
skin cells
stem cells

Stem cells

Explanation:

Stem cells have three general characteristics: (a) divide into cells just like themselves, (b) are undifferentiated, and (c) can generate specialized or differentiated cells.

Stem cells are undifferentiated because they have no tissue-specific structure that enables them to perform specialized functions such as producing saliva, contracting or transmitting nerve impulses. Stem cells are found in various locations in the human body and can differentiate into specific strains. They are cells with an indisputable vitality that can save lives, since numerous pathologies can compromise the physiological functioning of the body, leading to a great demand for treatment for the cure of diseases, trauma reversal or limb reconstruction.

the electromagnetic spectrum includes, from longest wavelength to shortest: radio waves, microwaves, infrared, optical, ultraviolet, x-rays, and gamma-rays.

i'd say that the moon rock is about 2.2 billion years old.