Your plant looks great, what your seeing is a very common occurrence of what happens when leaves are in constant contact with the grow space floor. You can suspend them using grobo drying racks if you wish. It is not going to have a significant effect in the grand scheme of things, you will be removing those leaves within the next couple weeks or so regardless.
What about the brown tips ?
Same cause I believe. So long as none of the symptoms are showing on your new growth, you’re in good shape.