There's no definitive answer to when El Misti first erupted. We don't have records that go back far enough to pinpoint the initial eruption.

Here's what we do know:

* Volcanoes have a long lifespan: El Misti is an active volcano, meaning it has erupted multiple times throughout its history.

* Lack of historical records: While we have records of some historical eruptions, they don't cover the entire history of El Misti.

* Radiometric dating: Scientists use methods like radiometric dating to determine the age of volcanic rocks, but even this doesn't give a precise date for the first eruption.

So, while we know El Misti has erupted for a very long time, the exact date of its first eruption is unknown.