Describe the two most important events in the history of animal life that occurred at the beginning and at the end of the Paleozoic era. (2 pts) List and briefly outline the six different periods into which the Paleozoic era is divided.
The two most important events in the history of animal life that occurred at the beginning and at the end of the Paleozoic era are the Cambrian explosion and the Permian mass extinction.
1. Cambrian Explosion: The Cambrian explosion took place at the beginning of the Paleozoic era, around 541 million years ago. It was a period of rapid diversification of life forms and is considered a significant event in the history of animal life. During this time, the majority of the major animal groups or phyla we see today appeared in the fossil record. This explosion of new life forms led to an unprecedented increase in the complexity and variety of organisms.
2. Permian Mass Extinction: The Permian mass extinction occurred at the end of the Paleozoic era, around 252 million years ago. It was the largest mass extinction event in Earth's history, wiping out approximately 96% of marine species and 70% of terrestrial species. The causes of this catastrophic event include volcanic activity, climate change, and oceanic anoxia. The Permian mass extinction had a profound impact on the course of evolution and paved the way for the rise of new life forms in the subsequent Mesozoic era.
Now, let's look at the six different periods that make up the Paleozoic era:
1. Cambrian Period: The Cambrian period marks the beginning of the Paleozoic era and is known for the Cambrian explosion. It lasted from around 541 to 485 million years ago and witnessed the rapid diversification of complex life forms.
2. Ordovician Period: The Ordovician period followed the Cambrian period and lasted from approximately 485 to 443 million years ago. It was characterized by the evolution of diverse marine communities, including brachiopods, trilobites, and early vertebrates.
3. Silurian Period: The Silurian period lasted from around 443 to 419 million years ago. It is known for the colonization of land by early plants and the appearance of the first terrestrial arthropods and jawed fishes.
4. Devonian Period: The Devonian period, also known as the "Age of Fishes," occurred from approximately 419 to 359 million years ago. It saw the evolution of diverse fish species, including lobe-finned fishes and early tetrapods.
5. Carboniferous Period: The Carboniferous period lasted from around 359 to 299 million years ago. It is divided into two epochs, the Mississippian and the Pennsylvanian. This period is characterized by the dominance of giant swamp forests and the formation of extensive coal deposits.
6. Permian Period: The Permian period was the final period of the Paleozoic era and lasted from approximately 299 to 252 million years ago. It is known for the Permian mass extinction, which dramatically reshaped the Earth's ecosystems and marked the end of the Paleozoic era.