Short answers, pulled from the story.
Perry Como's single "Catch a Falling Star" was certified as the first official RIAA gold record on the 14th of March 1958. The Oklahoma! soundtrack was certified as the first gold album a few months later.
The RIAA introduced the platinum certification in 1976, setting the threshold at one million units for albums and two million for singles. The Eagles compilation Their Greatest Hits (1971-1975) received the first platinum album certification on the 24th of February 1976.
Streaming has counted toward U.S. certification since 2013. The formula treats 150 streams as equivalent to one single sold, or one-tenth of an album. Since February 2016, RIAA Gold and Platinum Album Awards include both on-demand audio and video streams alongside track sales.
The first silver disc was awarded by Regal Zonophone to George Formby in December 1937 for 100,000 copies of "The Window Cleaner." The first gold record was presented to Glenn Miller and His Orchestra by RCA Victor on the 10th of February 1942, marking 1.2 million sales of "Chattanooga Choo Choo."
In the United States, gold certification requires 500,000 units, platinum requires 1,000,000 units, and diamond requires 10,000,000 units, applying to both albums and singles. Music videos follow a separate, lower scale.
IMPALA, the Independent Music Companies Association founded in April 2000, launched its own European sales awards in 2005 with a much lower entry point than RIAA. Its silver award begins at 20,000 units, and the scale runs up to double platinum at 800,000 units, designed to recognize pan-European success before the million-unit threshold.