This website contains age-restricted materials including nudity and explicit depictions of sexual activity.
By entering, you affirm that you are at least 18 years of age or the age of majority in the jurisdiction you are accessing the website from and you consent to viewing sexually explicit content.
Is it a reaction, then?
It was. It no longer is.
The reason I added this comment at all, was I felt the headline title was a little misleading. We have evidence, of a naturally occurring fission reaction on Earth, a long long time ago.