Question: How many particles have fallen to Earth from space?

Francesca Day answered on 10 Mar 2014:

That’s a great question! The short answer is no-one knows exactly! We can make a pretty good guess though. We think that most of the particles that fall to Earth from space are neutrinos. These are very small particles that are also produced in some kinds of radioactive decay. There are whizzing through you all the time, but you can’t feel them because they just go straight though you like ghosts.

Around a million million neutrinos fall on each square centimeter of Earth every second! Some of these neutrinos were produced in the Sun, and some were produced during Big Bang and have been flying through space ever since.

The Earth is over a billion years old and the whole surface of the Earth is a hundred thousand billion billion square centimeters. Therefore about one hundred million billion billion billion billion particles have fallen to Earth from space. That’s 1 followed by 44 zeros!