Question #2

The rock cycle is a process in which rocks are constantly changing between sedimentary, igneous, metamorphic, lava, magma, sediment, etc. and this cycle has been happening the whole time that Earth has been around because of plate tectonics and it will carry on happening until the Earth looses its energy and plate tectonics stop. Since the rock cycle has been changing old rocks into new rocks since the dawn of time, most of the rocks that were around in the precambrian era have gone through the rock cycle so many times - having the crystal make up changed so many times - that the rocks probably aren't even recognizable and the original rocks anymore. The rocks that we can find that actually date back to the precambrian era are so rare that we can barely find them. The rareness is due to the rock cycle and what I already explained. Although there is probably precambrian era rocks all around us, they're just not the exact same type rocks that were around in the precambrian because those rocks have already gone through the rock cycle many times over these billions of years. The rocks that we can find that are exactly the same would probably be rocks that have been close enough to the top of the Earth all these years to not have melted into magma, been far enough away from the heat to not become metamorphic, not had many more rocks and sediments go on top of it to pressure it into a metamorphic rock and not been so close to the Earth's surface or had something light over it that it hasn't been eroded by the wind, water, etc. These Precambrian rocks might be inside a mountain and if we dug far enough in, we could find some - but that's just a guess.