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
New type events?May 06, 2019
Tibia Summer Update 2019 - private test server invitationsMay 02, 2019
Golden Question of April - resultsMay 04, 2019
Discord for TibiaQAMay 01, 2019