The original Earth Day celebration was first brought to attention by environmentalist John McConnell in 1969.
Later, United States Senator: Gaylord Nelson suggested a separate Earth Day to be held on the 22nd April. The first documented celebration on the internet was in 2000. thanks to Al Gore.
The emote EarthDay was created by the Twitch.tv staff to support the cause, however the creator is unknown, but based on its importance, it was most likely a joint idea.
EarthDay is part of the original emotes collection that were uploaded to the site in the early days after its change in name from Justin.tv.
However, the original upload date is unknown, it is considered to be around the same time as the original Kappa emote was created in 2011.
As of 10/12/2019 according to the website StreamElements, EarthDay is the 60th on the list of most popular/used emotes on the website Twitch.tv, making it one of the more popular emotes.