What was the first thing that happened to a marble rock?

Answer 1

Marble started out in a marine environment on the sea floor. It formed coral reefs, the remains of sea life especially the shell living creatures. Then it was buried under other sediments, and this continued for millions of years. During this time the reefs and shells became compressed and heated. Further pressure and heating changed the rock from limestones and chalks into marble.

Eventually the tectonic movements of the earth caused the marble to be uplifted, then erosion removed the rocks over it and the marble was then exposed.

Marble is metamorphosed limestone and chalk. It retains the original chemical formula of CaCO3 and the streaks that you often see in marble is due to other substances like iron that were in the original limestones and chalks.