Does obsidian occur naturally

yes

Explanation:

obsidian is formed when lava cools

Yes. it can happen like glass by rapidly cooling.

                                      hope this helps!

above statement is not a true statement about the open ocean because the open ocean has low levels of nutrients. most of the photosynthetic activity on earth occurs in the open ocean within the photic zone. organisms in the deep ocean are exposed to frigid temperatures and total darkness but it does not begin at the low-tide mark.