Imagine the Earth devoid of human life, inhabited only by plants and animals. Would it still have a past and a future? Could we still speak of time in any meaningful way? The question "What time is it?" or "What's the date today?" - if anybody were there to ask it - would be quite meaningless. The oak tree or the eagle would be bemused by such a question. "What time?" they would ask. "Well, of course, it's now. The time is now. What else is there?"