Final answer:
Plants and fungi first became established on land during the (B) Paleozoic era, specifically more than 500 million years ago during the Ordovician period, with the emergence of early land plants and terrestrial fungi.
Step-by-step explanation:
Plants and fungi first became established on land during the Paleozoic era. The Paleozoic is an early geological era, divided into six periods including the Cambrian, Ordovician, Silurian, Devonian, Carboniferous, and Permian. It is during the Ordovician period, more than 500 million years ago, that the colonization of land by the ancestors of modern land plants is marked. Furthermore, fossil records show that fungi colonized land at least 460 million years ago, which precedes the invasion of ancestral freshwater plants onto dry land.
The oldest fossils of land plants date back about 470 million years, and they likely resembled modern liverworts. This information corresponds with the evolutionary timeline where prokaryotes came first, followed by protists, and then fungi, plants, and animals branched out. Therefore, the correct answer to the question is B. Paleozoic.