This article is from the Final-Fantasy and other Square Soft Games FAQ, by firstname.lastname@example.org (Nick Zitzmann) with numerous contributions by others.
You need to take the Vampire's Ruby, leave the cave, and give the ruby
to the titan in a cave to the northeast of the Earth Cave. You'll now be
able to pass through the cave and talk to Sarda. Sarda will give you a
rod which will allow you to reach the bottom of the Earth Cave.
Take some Soft Potions with you, because the bottom two floors of the
Earth Cave have lots of Cockatrices living in them. Cockatrices can turn
a character to stone in one attack, making them the second most annoying
monsters in the game behind the Sorcerers (who can kill a character in