Is there any authoritative reference to the claim that glass decomposes in one million years? I came across that figure multiple times (for example, 1, 2, 3). They often cite The New Hampshire Department of Environmental Services which, in turn, cites "U.S. National Park Service; Mote Marine Lab, Sarasota, FL." (some websites cite the latter directly), but I couldn't find this elusive primary source (I scoured several Google search pages). The last link (the word "websites") includes this reference: "Sources: U.S. National Park Service; Mote Marine Lab, Sarasota, FL and “Garbage In, Garbage Out.” Audobon magazine, Sept/Oct 1998." But an article that has such a title doesn't contain any information about million-year decomposition – and maybe it's not the article in question because it's dated differently. Is Skeptics SE going to help me out?
The oldest preserved glass formed 300 million years ago
The statement is in chapter 4 "Weathering of Slags" by Jakub Kierczak, Anna Pietranik and Nadine M. Piatak
Some of these glasses have been in the natural environment for about 300 million years with low alteration rates of only tenths of a millimetre per million years.
However, as far as some supposedly authoritative reference claiming one million years, Environmental and Workplace Safety: A Guide for University, Hospital, and School Managers (1996) at page 256 say:
A glass bottle takes one million years to decompose
The 21 September 1972 New York Times article NATURE RECYCLES CANS, BUT SLOWLY says:
Perhaps the least perishable of the commonly thrown‐away materials is glass. Prof. Evelyn C. Marboe, a glass chemist, said a bottle left on the forest floor might not break down into sand‐sized particles for a million years.
“Glass is one of the most durable materials known,” Professor Marboe said. “We have glass beads from Egypt that are 4,000 years old and, of course, there are many examples of glasslike rock—such as obsidian—that may be as old as the earth.”
So people saying "one million years" for glass bottles goes back at least to 1972, but really glass can last much longer.
The South China Morning Post reports that some glass beads from an asteroid collision lasted over 3 billion years - far longer than the suggested 1 million years:
[Glikson and Hickman] found tiny glass beads, called spherules, which are formed by vaporised material from an asteroid's impact [...] It dates from 3.46 billion years ago.