What would an untended Earth look like in a hundred years?

I'm trying to write a short story, and I'd like to add a little realism to it.
Basically, I would like to know what a city would be like in a hundred years
if there was no one there to care for it.

Suppose one day, all the people on Earth are captured by aliens (not my story,
but it illustrates the situation). They come back in exactly a hundred years.

What happens to asphalt roads if they aren't repaired or used? Would a road
still be recognizable as such if it was left to the elements for a hundred
years? And what would it look like?

How about concrete streets? How do they break down?

In cities, would buildings still be standing, or would they all be rubble? In
the suburbs, would wood frame houses or even brick or adobe houses still be
there? I know that some of the answers depend on the climate. Los Angeles
would have a better time of it than New York, for instance, due to the effects
of the winter weather and the freeze/thaw cycling.

How about farmlands? Would they still have some remnants of their crops, but
probably mixed with weeds?

How about manmade things? Would a car be completely dissolved into a pile of
rust for steel, white Aluminum Oxide for Aluminum, or (I don't know what) for
plastic/fiberglass? Would the engine still be there? Would there be some cars
that would not be touched (like a 1965 VW Beetle)?

So generally, what kind of decay would I expect to see after a hundred years?

Jerry
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