Why is it difficult to interpret the rock record of precambrian time?

1. The record is incomplete due to burial, erosion, etc.
2. Much, if not all, are metamorphosed
3. There are (for the most part) no fossils to help with depositional environments or age dating
4. Things worked differently in the Precambrian: limestones were formed different, dolomites may have been primary, detrital systems did not behave the same way (lack of meandering fluvial, for example), reduced atmosphere that enabled mobile Iron that made banded-iron formations, some igneous rocks only formed then and do not form today (i.e. kimberlites), etc

This is all you, but i can give you some topics that you could try. if it rained when you want to do something outdoors, it 'limits' that human activity. maybe you want to do an experiment that goes throughout the whole year and you have to have above freezing the entire year. this 'limits' your activity. i thought of those just off of the top of my head. something that gets to me that might be getting to you is you are thinking too hard about what to do. think simply, and if it is too simple, then bump it up just a little bit.