Objectively prove? Nothing. But subjectively there is a stark difference in the quality of suggestions and apparent depth of understanding from earlier LLMs. E.g. 3.5 suggested using jeans for radiation shielding "because denim is a thick material".

I did try a web search and directly asking the model for references. Unsurprisingly jeans for Mars colonization doesn't seem to be an existing concept, so it's almost certainly not in the training set.