Question 2

It is true that precambrian rocks are very rarely located on the surface of the earth. The reason for this lies in the rock cycle. The word "cycle" is connotative of constant change and rotation, which is exactly what occurs. Sediment, the original bits and pieces of mineral and material, is buried and compacted in the earth, and after many years can form sedimentary rocks such as limestone. After a great deal of time, under the right conditions of heat and pressure, these sedimentary rocks can transform in to metamorphic rocks. These are generally buried deep under the ground, and can sometimes find their way to a plate tectonic hotspot. Here they might be heated until they turn in to liquid magma, only to be ejected on to the surface via volcano, where when they cool they become known as igneous rocks. Then these are broken down by erosion in to sediment, and the so called cycle begins anew.

2 problems exist in this for finding Precambrian minerals on the surface today. One being that over the millions of years, the rock once on the earth's surface has been through the cycle at least once or maybe more. It could be buried thousands of miles below. The more pressing issue, however, is what the incredible exertions of the rock cycle do to the actual samples. It tends to destroy and reform the makeup of the rocks; thusly, most precambrian samples have been effectivley destroyed by our own earth. Finding ones that have come back to the surface and or escaped the ravages of time and the rock cycle are incredibly rare, and this is the answer to the posed question.