Step 1: Concept Identification:
This query seeks the historical date of the inaugural observance of Earth Day, an annual event dedicated to showcasing support for environmental protection.
Step 3: Comprehensive Elaboration:
The inaugural Earth Day commenced as a grassroots initiative on April 22, 1970. Spearheaded by US Senator Gaylord Nelson, it was conceived as an environmental educational session. This event galvanized millions of Americans and is recognized as the catalyst for the contemporary environmental movement. Its impact included the establishment of the United States Environmental Protection Agency (EPA) and the enactment of pivotal environmental legislation.
Step 4: Conclusive Response:
The first observance of Earth Day occurred on April 22, 1970.