5. 300 million year old screw
In the 1990’s, a Russian research team found a peculiar object in the Kaluga region after an asteroid strike. The object appears to be a 300-million-year-old screw fixed in a rock. Most people agree that this is evidence of either aliens or a highly advanced human civilization. The object was collected by a UFO and paranormal research team, who found a second screw in the same rock after the x-ray examination. No further details have been published.
Some scientists, however, believe that the object is actually a fossilized sea creature called a crinoid. Nowadays there are only 600 species of crinoid, but they were widespread million years ago. There is one problem with this explanation though: crinoid was a lot smaller and had a bit different markings.
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