The temperature began to rise at the center of the solar nebula because

At the center of the solar nebula, the temperature would begin to rise because the nebula is contracting and therefore is increasing the motion of the atoms. The solar nebula is a proposed explanation of how the solar system was formed. It was believed it was from a collection of gas and dust called a nebula cloud.

Nation of conflicting ethnic groups

Answerequatorial guinea,gabon, and western sahara;