Halley's comet came to earth.

It seems that the landlord still has a little faith in your classmate's statement. It is estimated that the classmate's statement was also seen somewhere on the Internet.

I remember reading an extremely funny article about Renren.com, saying that Qigong was bought with a comet, and then I felt with my mind that the green virus on the comet was introduced into his body. I believe the landlord has a general understanding of the truth of this statement. The standard folk science is widely reproduced in astronomical pages as a joke by astronomy enthusiasts.

Is this possible in rigorous science? Let's look at an example first. 19 10, the earth entered the tail of Halley's comet, which caused great panic in the society at that time. The argument of the end of the world is much worse than today (no one will really believe that today is 20 12 and then commit suicide? There were many such people at that time). But when the earth came out of the tail, everything was as usual. This event led to a leap in human understanding of comets. Except for water, dry ice, ammonia and other extremely sparse substances, the impact of comet tail on the earth can be ignored.

Let's see if this classmate's statement is accurate biologically. If it's a virus, there must be genetic material. There are only two genetic materials, DNA and RNA. Either way, there are three basic raw materials, amino acids, sugar and phosphoric acid. But there may be some simple organic matter on comets, but there is no evidence and it is unlikely that amino acids, sugars and phosphoric acid exist. Finally, even if there are these three things on the surface of a comet, can it become a living body? Still no, there is no liquid water to block ultraviolet rays, even if more complex chemicals are formed, they will be interrupted by ultraviolet rays. How can there be life without living polymers?

So your classmate's statement is not very clever in folk science. It can be completely refuted from both astronomy and biology.

Are you afraid now?