... A powerful electron microscope found more than 100,000 particles on old the JCPenny tie, including cerium, strontium sulfide and pure titanium.
“These are what they call rare earth elements. They’re used in very narrow fields, for very specific things,” said Tom Kaye, lead researcher for the group that calls itself Citizen Sleuths.
Kaye said the elements were rarely used in 1971, during the time of Cooper’s daring leap with a parachute from the passenger jet
This is interesting, but I suspect its face-value significance is being overestimated ...
Cerium is the only 'rare earth' among the three listed trace findings. It's had commercial applications (e.g., lantern mantles, lighter flints) since the late 19th century. Cooper smoked, so he presumably used a lighter.
Titanium was in use in the military aerospace industry as early as the 1950's, and by the late 1960's it was commonly found in commercial aviation applications (e.g., engine components) as well.
Strontium sulfide has long been widely used in the glass and ceramic industries.
The combination of cerium and strontium sulfide has long been studied and employed for its electroluminescent properties, though I can't find any confirmation that any EL devices based on this combination were in use as early as 1971.
Owing to this combination's electroluminescent properties, it's been employed in electrophoresis processing of fragmentary DNA / RNA samples.
The FBI conducted DNA / RNA testing on trace materials from the Cooper clip-on tie in 2001. For all we know, at least some of these cited materials represent residues from that testing.
In any case, there would need to be a lot more detailed information provided on the specimen's (tie's) initial acquisition, storage, chain of custody, etc., before one could reasonably presume any trace materials found on the tie nowadays actually date back to the 1971 event.