Final answer:
The Paleozoic Era is marked by the appearance of complex life, including trilobites, and lasted from 544 to 245 million years ago. It began with the Cambrian explosion and concluded with the Permian extinction. The correct answer is (c) Paleozoic.
Step-by-step explanation:
The Paleozoic Era began with the appearance of complex life, including numerous forms of marine life such as trilobites. This era is often referred to as the age of "old life" and lasted from approximately 544 to 245 million years ago. Marked by a significant event known as the Cambrian explosion, the Paleozoic Era gave rise to a vast diversification of life, including the first emergence of vertebrate animals. These ancient organisms populated the oceans, and over time, evolutionary advancements allowed some species to move onto land. The Paleozoic Era's conclusion came with the Permian extinction, which represented the largest mass extinction event in Earth's history at that time.
Trilobites are particularly noteworthy as they are one of the first complex forms of life appearing during the Paleozoic Era. They thrived following the Cambrian explosion and are one of the most recognizable fossils from this time. The presence of trilobite fossils is indicative of the Paleozoic Era and not the Mesozoic, Cenozoic, or Archean eras. Consequently, the correct answer to the student's question is option (c) Paleozoic.