Historically, Poland has been part of the barrier against the steppe invassions, first the Mongols, then the Russians themselves. From that point of view, it would be central Europe, as the steppe peoples would be eastern Europe. Poles often lived within the HRE, which would place them squarely in the Mittel-europa.
The Cambrian Explosion refers to the metaphorical explosion of life that began 542 million years ago and lasted for roughly 40 million years. This lesson will cover the events that occurred during this time period.
The Cambrian Explosion is a sudden appearance of all life as we know it. There are exceedingly few that come before this and those that follow the Cambrian show no differences than their ancestral cousins or predecessors that follow. It is like an explosion of life that appears almost instantaneously on earth. What is amazing about the Cambrian layer is what is not there before it and after it. In other words, you will find almost no predecessors or ancestors of the Cambrian creatures; that is, absolutely nothing above or below this layer.