"Chemical clues" refers to small traces or hints in the form of chemicals that can provide important information or help solve a mystery. Full definition
A young star with planets forming, illustrated here, may retain chemical clues about the worlds that surround it. (discovermagazine.com)
They also formed before the atmosphere gained oxygen, roughly 2.3 to 2.4 billion years ago, and so preserve chemical clues that have disappeared in modern rocks. (sciencedaily.com)
Chemical clues in skeletons produced by coral growing at Kiribati contain a newly discovered warning. (scientificamerican.com)