About these "calamities" and "Astral/Umbral" eras...

[Zohar_Lahar]

I actually thought it might have fallen through the cracks entirely and might be a fun question to just ask ... but much to our surprise, Banri Oda-san has barred discussion of the topic because it was planned from the beginning and hasn't been revealed yet. The only hint I can think of is that Naoki Yoshida-san was very proud of Ravana being the first summon created specifically for FFXIV - so whichever entity it was, it was a traditional summon. That should narrow it down! (...Oh.)

The problem is, the Gnath appear to live in Dravania (opposite end from Ala Mhigo), so I doubt they would've summoned Ravana at that point.

[Frederick22]

Well we know that Othard had summoned Primals during their war with the Garleans and this was well before the seal was broke in Silvertear / Paragons teaching the Beast tribes. Really there's so much confusion with Primals and their entire nature, the definition is just way too broad at this point .

When it was said that there were primals on Othard? I dont remember nothing about that on main scenario. Infact what I do remember is that Yugiry said that the primals where something unknow on Doma, Levhiatan was the first primal she has ever see. I think you got it wrong, there arent primals on Othard. Just by adding Doma is a nation of the continent of Othard.

[Enkidoh]

The main FFXIV site states it here:

The eastern nations were the first to feel the newborn empire's mighty fist. It was during this campaign that the emperor witnessed firsthand the destruction wrought by the primals—an experience that led to an imperial mandate for their annihilation.

Yugiri also confirmed that although the Eorzean term 'Primal' was unknown to her, once the Scions actually explained what a Primal was did she understand and acknowledge that Primals do in fact exist on Othard (in most likelihood, as Doma was a client state of Garlemald she probably knew the Primals under the Garlean derogatory term of 'eikon' instead): (spoilered for new players just joining us):

Yugiri: "I take it something ill is afoot?"
Y'shtola: "Aye. A primal is about to be loosed upon Eorzea."
Yugiri: "A.. primal?"
Y'shtola: "A godlike being whose very existence is a bane upon the land. We Scions of the Seventh Dawn are sworn to put an end to their kind."

and

Yugiri: "Beings held as gods also exist in what you call the Far East."
Yugiri: "Legends tell us that they walked among us in days of yore, but I confess that I never truly believed them. That I should live to behold one is... humbling and horrifying in equal measure."
Yugiri: "Now that I have come face-to-face with a Primal, I do begin to understand why the Garleans fear them so."

[Frederick22]

Wow I have complete not see that part. Also I thought the Garleans's first encounter with a primal was on Eorzea. My apologies.