Looking for the name for a science fiction film from the 1990's or 2000's about a group of scientists that travel in time and accidentally bring back a small piece of dirt in the sole of one's shoe, a particle that alters the balance of nature and produces a catastrophic and out of control growth of vegetation on earth, swallowing everything gradually. It's not Day of the Triffids, though, and it includes space/time travel.
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