I would particularly agree with an ice field rune. But about being the only one missing, I got a wild theory here related to that: Technically poison was considered an earth damage only after the update on 2007 (8.1). Before that, we had poison as a different kind of damage, not directly related to the earth damage. So we can think that an "earth field" is something that we had only because poison became part of it. Cipsoft never implemented maybe because they never really thought about adding a field for each of the four basic ones at all (although the earth damage got one field as a collateral effect of the adjustment of poison integrating the element earth), but it is something up for discussion.
More details about 8.1 can be found here: https://www.tibiawiki.com.br/wiki/Updates/8.1
Is it possible to make a question as a poll at TibiaQA?July 01, 2019
Looking for a social media managerJune 09, 2019
Extra points on TibiaQA for questions with high amount of viewsJune 18, 2019
See which of your posts got downvotedJune 13, 2019