Earthstrike

Earthstrike is a trinket that increases melee and ranged attack power for a limited time. This is the physical version of the Talisman of Ephemeral Power.

Source
Earthstrike is a quest reward from the quest Champion's Battlegear which starts with Vargus in the Cenarion Hold in Silithus. To complete the quest, you must turn the following items to Vargus:
 * 15 Cenarion Combat Badge
 * 20 Cenarion Logistics Badge
 * 20 Cenarion Tactical Badge
 * 1 Mark of Cenarius

You must also have Exalted reputation with the Cenarion Circle.

Effective Attack Power
Assuming this trinket were activated every cooldown, it would grant an effective: 280 * 20 / 120 = 280 * 1 / 6 = 280 / 6 = 46.66 Attack Power