Detailed Instructions: Given a scientific passage and an answer, generate a question for the given answer.
Q: Passage: Plants may have colonized the land as early as 700 million years ago. The oldest fossils of land plants date back about 470 million years. The first land plants probably resembled modern plants called liverworts , like the one shown in Figure below . Answer: 470 million years
A:
The oldest fossil of land plants date back how many millions of years?