Final answer:
The Precambrian represents the longest duration of geologic time, covering from the formation of Earth to the start of the Phanerozoic eon.
Therefore, the correct answer is: option 1) Precambrian.
Step-by-step explanation:
The Paleozoic, Mesozoic, and Cenozoic are eras within the Phanerozoic eon, which followed the Precambrian. And, the longest duration of geologic time among the options provided is the Precambrian.
This "super" eon encompasses the Hadean, Archean, and Proterozoic eons and represents the majority of Earth's history, spanning from the formation of Earth about 4.6 billion years ago until the start of the Phanerozoic eon about 541 million years ago.
The Paleozoic, Mesozoic, and Cenozoic are eras within the Phanerozoic eon, which followed the Precambrian. Chronologically, the Precambrian is followed by the Paleozoic era, then the Mesozoic, and currently, we are in the Cenozoic era.
The Paleozoic era is notable for being the era of "old life" and includes major events such as the Cambrian explosion and the Permian extinction.
Following the Paleozoic, the Mesozoic era is often known as the Age of Reptiles and leads up to the current era, the Cenozoic, which includes significant epochs in the evolution of life on Earth. Among the four, the Precambrian is by far the longest and covers the largest span of Earth's history.