Step 1: Understanding the Concept:
This question asks for the historical date of the first celebration of Earth Day, an annual event to demonstrate support for environmental protection.
Step 3: Detailed Explanation:
The first Earth Day was a grassroots movement that took place on April 22, 1970. It was founded by US Senator Gaylord Nelson as an environmental teach-in. The event mobilized millions of Americans and is credited with launching the modern environmental movement. It led to the creation of the United States Environmental Protection Agency (EPA) and the passage of landmark environmental laws.
Step 4: Final Answer:
The first Earth Day was celebrated on 22 April, 1970.