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.
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The two most significant events in the history of animal life at the beginning and end of the Paleozoic era are the Cambrian explosion and the Permian-Triassic mass extinction.
1. Cambrian explosion: This event took place around 541 million years ago, marking the beginning of the Paleozoic era. During this period, there was a sudden and remarkable diversification of complex multicellular organisms. It is often referred to as the "explosion" because a wide range of new body plans and anatomical structures emerged, leading to the rapid evolution of various animal phyla. The Cambrian explosion was a significant event as it marked the origin of the majority of animal phyla present today.
2. Permian-Triassic mass extinction: Occurring approximately 252 million years ago, this event signified the end of the Paleozoic era. The Permian-Triassic mass extinction is known as the most devastating extinction event in Earth's history. It caused the eradication of approximately 96% of marine species and around 70% of terrestrial species, including many dominant groups at that time. The cause of this mass extinction is still debated, but it is believed to be a combination of volcanic activity, climate change, and asteroid impacts. The Permian-Triassic mass extinction had a profound impact on the subsequent evolution of life on Earth.
Now, let's outline the six different periods in the Paleozoic era:
1. Cambrian Period: This period spans from approximately 541 to 485 million years ago. The Cambrian period is known for the Cambrian explosion, during which most of the present-day animal phyla evolved.
2. Ordovician Period: Occurring from around 485 to 443 million years ago, the Ordovician period witnessed the evolution of diverse marine life forms, including marine arthropods and jawless fish.
3. Silurian Period: Taking place from approximately 443 to 419 million years ago, the Silurian period is known for the colonization of land by early plant and animal life. It also marked the emergence of jawed fish.
4. Devonian Period: Spanning from around 419 to 359 million years ago, the Devonian period saw the "Age of Fish," with diverse fish species dominating marine and freshwater ecosystems. Land plants continued to evolve, leading to the first forests.
5. Carboniferous Period: Occurring from approximately 359 to 299 million years ago, the Carboniferous period was characterized by vast swamp forests that eventually formed extensive coal deposits. The first amphibians and reptiles appeared during this period.
6. Permian Period: Taking place from around 299 to 252 million years ago, the Permian period saw the diversification of reptiles and the emergence of mammal-like reptiles. However, it ended with the Permian-Triassic mass extinction, the most severe extinction event in history, leading to the end of the Paleozoic era.