In 1910, Halley's Comet passed extremely close to the Earth - so close,
in fact, that the Earth passed through the tail of the comet in May 1910. As
the date arrived, many people worried that life on Earth would be
extinguished by all of the poisonous gasses that would flow onto the Earth.
Their fears were unfounded (my grandmother remembered this, by the way).
Why? Explain why such worries were not based in fact given what we now know
about comets and their tails.