The asterisk represents the origin of replication what enzyme binds here

Then enzymes  in repair synthesis and ligation put together the new synthesized stretches of DNA to make a continue of strand contains only DNA.  DNA ligase is a link the main enzyme for DNA replication; incitation of the covalent bonding of the 39 end of a new DNA fragment to the 59 end of a growing chain. 

layer 3 is younger than layer 6.

all these collisions do one thing, and that thing is explained in the last option. when dusst, rocks and ice collide, they harden and form giant layers of rocks or hard ice.

d)   to harden materials to form different parts of earth’s layers

hope it ,

bioteacher101