Why do creationists assume that these objects are 'man' made? Surely it could be argued that these objects could be made by a completely different species. If we evolved from apes in a few million years, couldn't a similar thing have happened countless times before in the past from a different species?
Dinosaurs were around for many hundreds of millions of years. Isn't it possible that a species of dinosaur evolved a bigger brain, language, art, technology and culture? They may have looked very human-like but wouldn't be human. Jump forward in time ten million years. Do you really think humans will still be ruling the planet?
How much evidence of our existence will be around? Even plastics biodegrade in just a few thousand years. It is completely plausible that a new species could evolve to become sentient and have it's own culture and beliefs.
If it has happened once, it has probably happened at least once more in the past and will happen many more times in the future. I find the thought very humbling.