Casting another Earth Totem will destroy the elemental.
Elementals have a fairly large aggro range and may cause problems in instances by attacking mobs that were not otherwise in combat, much like Searing Totem. The elemental is not aggro-linked to the shaman, and when it dies the mobs will reset as long as no one else is on their threat list. Elementals move surprisingly quickly, and use an AoE taunt ability frequently.
This is mainly a tanking minion and is not the best for damage.
Earth elementals have a fair amount of health, roughly as much as the shaman; as such, while they excel at handling mobs out in the world, elite monsters will kill them rapidly.
Earth elementals deal physical damage, but as with any earth elemental, they are immune to all Nature spells and effects.
In instances, the primary use for Earth Elementals is to serve as an emergency aggro magnet. Their AoE taunt will almost always gain the attention of any mob that is affected by it - while monsters focus their attacks on the elemental, they are gathered up for another player, preferably the tank, to deal with. As such, they serve as a bit of an "Oh no!" totem.
The Earth Elemental is a great soloing companion for harder (group) quests. Certain quests that normally require a 3 or even 4 man group can be soloed with an Earth Elemental Totem and a competent shaman. A good tactic involves constantly switching between healing the elemental, healing yourself, and dealing damage.
Patch 6.0.2 (14-October-2014): Totems will no longer cause hostile creatures to enter combat with the Shaman based on proximity.; Earth Elemental deals 90% less Auto Attack damage but generates 1000% more threat.
Patch 5.4.0 (10-Sep-2013): Earth Elemental Totem's summoned Greater Earth Elemental will no longer taunt off players that are in a tanking specialization.
Patch 5.1.0 (27-Nov-2012): All totems are now considered spells, and summoning totems can be prevented by silencing effects. Searing Totem, Magma Totem, and Fire Elemental totems fall into the Fire school, while all other totems fall under the Nature school.
Patch 5.0.4 (28-August-2012): The cooldown for this totem has been reduced from 10 minutes to 5 minutes, at level 58.
Patch 3.3.0 (08-Dec-2009): The cooldown for this totem has been reduced from 20 minutes to 10 minutes. Cannot be used in Arenas.
Patch 3.1.0 (14-Apr-2009): The summoned Earth Elemental should now have significantly more health and slightly more armor. Now scales up in power based on the shaman's spell power instead of attack power.
/Patch 3.0.2 (14-Oct-2008): All totems are now considered on the "Physical" school, and no longer magical spells.
Patch 2.4.3 (2008-07-15): This pet will now leash back to its totem when pulled beyond 50 yards away.
Patch 2.4.0 (25-Mar-2008): The Global Cooldown of all Totems has been reduced to 1 seconds, down from 1.5 seconds.
Patch 2.1.0 (22-May-2007): This pet will now come into the game with full health, including that gained from a percentage of its master’s stamina.