ST.Nick, I believe that is heat stress from being overdried or having dry pockets in your soil. That is one of the reasons I personally don't care for growing in soil, if you don't get it mixed with stuff that keeps the soil from compacting, it will develop hard, dry spots that will kill the roots.
Also, I hate not knowing (or controlling) what's happening in my medium. If you go with soil that is organic, you have to take care of the organisms in the medium that make organics work. If you grow in any medium that has synthetic nutrients added then you have to manage the chemistry of that medium. Both ways can sound difficult but its just a matter of deciding on your likes and dislikes then learning the process, and then perfecting the process for your setup.
Emma: Welcome to MARP, Don't let our seriousness scare you away, just let it scare you enough to do some serious homework before you even buy seeds. The seeds should be the last thing you get or they will be the first thing you do, and
that will lead you to grief if you aren't ready. There is a lot to doing this (especially if you want to grow indoors) but if you do some reading and asking questions, we can get you through your first grow, which is the first and often most difficult of about 4 learning curves. But we are happy to help you.