If the marble or granite is good quality it will not wither because of normal weather conditions. This marble is much thicker than the standard and should have been fine. Keep in mind that most if not all granite yards keep their granite and marble stored outdoors at all times; if there was a threat of weathering that certainly would not be the case. Even so it is important to know that marble is more pourous than granite, that is why it is not recommended in kitchens or high wear and tear areas. So to answer more clearly, it was not the sun or any other weather related substance, the quality from the start was probably not best. I hope this helped
