The nucleotides in a base pair are complementary which means their shape allows them to bond together with hydrogen bonds. The A-T pair forms two hydrogen bonds. The C-G pair forms three. The hydrogen bonding between complementary bases holds the two strands of DNA together.
As shown in the picture I attached to my answer, we can see all of the tectonic plates, which make up the lithosphere. The pieces do move very slightly every year.
