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.
Later life forms that appeared during the Cambrian Explosion include Arthropoda, Brachiopoda and Echinodermata. It is estimated that there was as much diversity of life in the oceans 542 million years ago as there is today. One of the most successful life forms during the Cambrian Explosion were trilobites.