So now you know your marble floor probably wasn't sealed before it was installed. Not a big deal. That can be done at any time - so long as the stone is dry.

Marble is very porous and LOVES to grab any form of moisture it can. Including hairspray, toothpaste, perfume, water, etc.

A sealant will reduce the water penetration but it won't stop etching. Etching is when a slightly acidic/basic product hits the surface of the marble and reduces the gloss level of the finish. This is normal. It is natural. It is what marble does. If you see this, relax and let it be.

Marble can be refinished! Yep. For a few dollars a square foot, you can hire someone to come in and buff up/seal the floor when ever you feel it needs it (ie. when YOU want to...the stone doesn't *need anything).

Enjoy your new floors. They are marble (this is one way to verify they are real stone!) and marble does these types of things. You can seal them to stop this type of water penetration. You can also refinish them (every 10-15 years or so...just to make them lovely again). That's what makes stone so special. It should outlast you and the house!