What outlandish conclusions can be drawn from fossils formed today?

A lot of it would depend on what these aliens look like, right?

If they’re bipedal humanoid rubber forehead aliens, they’ll probably figure out the approximate function of most of our stuff–even if we get stumped by stuff in the past, we can still recognize the most basic tools of life (and man-made objects tend to be very, very obvious as such). In fact, the simpler the tool, the easier it is to tell what it is. A hammer from 10,000 B.C. is instantly identifiable as such in the present day because “large, heavy object with a flat surface on a stick that, when swung, produces blunt force” is something we still need and use every day. And we keep a ridiculous amount of records on stuff that isn’t immediately degradable. Yeah, digital records will be a total crapshoot: even if they can get past encryption and understand binary, they may not know why some dude bothered to tell a computer to output “HELLO WORLD”. But I think enough of everything else will survive for them to be able to at least piece together bits and pieces of our language, culture, and religion. They may not get us right in the details, but certainly in the gist.

If the aliens are truly alien, then anything goes. Even a human being can creatively interpret a house as “large immobile creature with concrete and rebar skeleton, drywall and skin, and scaly top covering that is infested by parasites”. (Insert tongue in cheek comment about future alien Dopers arguing about evolutionism versus creationism with regards to a pocket-watch.)

A Stephen Jay Gould of fossicking around in 1000,000 AD would look at the fossil record of squirrels in the British Isles and find that a dramatic change in its skeletal structure and genotype occured about 1900-2000 AD, give or take 50,000 years.

In reality, the imported American red squirrel, a late interloper, pushed out and replaced the original grey squirrel from its habitat. The future SJ Gould would quickly come out with an evolutionary theory that he would probably call “punctuated equilibrium” to account for the sudden and mysterious change in the fossil record of squirrels.