Ferns and reptiles appeared in era

Ferns and reptiles appeared in the paleozoic era.

Ferns and reptiles appeared in the Paleozoic era.

Paleozoic is the longest of the Phanerozoic eras, and is subdivided into six geologic periods (from oldest to youngest): the Cambrian, Ordovician, Silurian, Devonian, Carboniferous, and Permian. The Paleozoic comes after the Neoproterozoic Era of the Proterozoic Eon, and is followed by the Mesozoic Era.

The correct answer is "atomic weight".

Idon't see the pic?