Final answer:
Whisk fern-like fossil plants have been discovered dating back to the Paleozoic, which is around 350 million years ago, much older than any of the options provided.
Step-by-step explanation:
Fossil plants that resemble modern whisk ferns have been found and date back to a significant period in the Earth's history. The first land plants probably looked like liverworts and appeared around 470 million years ago according to the fossil record. Over time, plant evolution led to the diverse flora we see today, including ferns and fern-like plants. The fossil record, including discoveries such as the Rhynie chert and fossilized stromatolites, provides important evidence about the history of life on Earth. While whisk ferns seem more recent, fern ancestry takes us back to the Paleozoic, which implies plants with characteristics similar to whisk ferns could be much older than any of the options listed in the question.
Fossil plants that look like whisk ferns have been found and are as much as 800 million years old.