How did Flood Form?

Community Halo Universe
1

I have been always been wondering how Flood has came to be. Like was there a very first Grave mind and if so how did it form?
I know it has existing for a long time, into a time for Forerunners but just wondered how did it just come to be.

2

You can read everything you need to know about the Flood here.

3

OOo ta, my saviour.