If you've ever seen a plane flying overhead, you're probably familiar with the cloud-like path they leave in their wake. They're condensation trails (or "contrails" for short) made up mostly of ice crystals -- but to conspiracy theorists, they're something far more sinister. They call them "chemtrails" and they're supposedly filled with harmful chemicals... According to most major conspiracy theory news sources, chemtrails are a real and persistent threat to human existence. However, beyond that overarching theme, the specific allegations of what's in them are diverse, and frankly quite bizarre. The general idea is that these chemtrails are being used by the government to dump harmful biological agents on the unsuspecting population. Why exactly they're doing that depends on which school of "chemtrail thought" you fall under.

But before we get into the nitty-gritty, let's talk science.

The theory that the government is using commercial airlines to dump chemicals on Americans has no scientific basis whatsoever. Those clouds you see in the sky are normal water-based contrails that are left behind aircraft under certain environmental conditions. According to those who have taken the time to study contrails, they form at such high levels in the atmosphere that even if they were full of chemicals, the pollutants would be substantially diluted before they reached the ground.

Now IF -- and that's a big if -- chemtrails are somehow real, despite all the evidence to the contrary, what might they actually contain?

Some theories state that the chemtrails contain chemicals like barium, aluminum salts, polymer fibers, thorium, or silicon carbide. The purpose of these chemicals, they say, is to suppress the more fantastic elements of our human DNA. The reason for this is because the shadowy world government is operating under orders from the Reptilians (an alien race with nefarious purposes).