Problem with White Widow grow

My plants are only 3 weeks old and the heat is immense... I believe that's the reason this happened, however I'm not certain... anyways, the bottom leaves are all dry and dead while the top bushels (6-8 leaves) are ok... I snipped the dry yellow leaves and am hoping for new growth soon.

Can someone verify that the heat is what did this? I can provide pics if necessary

you should provide pics it will help understand more.But from the sound of it more than likely it is heat stress.