Here on the level sand
Between the sea and land,
What shall I build or write
Against the fall of night?
-- A.E. Housman
I first encountered this phrase in Greg Bear's book Moving Mars, where one of the main characters uses it to describe the feeling he gets from being inside the shell of a gargantuan, prehistoric Martian mother Ecos. As far as I know there is no official definition of deep time, but I have seen it used in many contexts.
In paleontology, "deep time" refers to time occuring on a scale that is virtually inconceivable to humans. How do we visualize the world as it was two billion years ago? How might one person's thoughts encompass the number of years it takes for a glacier to carve a valley except through sloppy analogy, such as envisioning the number of grains of sand on a beach?
In an excellent essay on the topic (available at http://www.authorcafe.com/benford/articles/deeptime.html), Gregory Benford uses the term to refer to cosmological timeframes, in which it's not uncommon to talk about events fifteen billion years in the past as if they'd happened just before lunch last Tuesday--the formation of our galaxy being a great example of such an event. Benford raises the question: how can humanity preserve knowledge on the grand time scale? How to communicate with those who will come after us? For a species that has become used to the idea of immortality through ideas, it makes us mighty uncomfortable to consider that ideas themselves only last as long as their underlying medium--the cultural and linguistic context in which they arose.
Have you ever been to a landmark that simply radiates history? I'm talking about the kind of place that seems eternally still even though it's twenty meters up the side a wind-blasted red rock formation in the middle of the Mojave Desert. The kind of place where you can sit cross-legged, close your eyes, feel the sun on your face, listen to tree limbs creaking in the breeze, and know that the day would feel much the same if you were sitting there 10,000 or 100,000 years ago. I contend that it is also quite valid to use "deep time" in describing the feelings one takes away from these places. Landmarks being more accessible than literature to the average seeker, I would even argue that "deep time" in this sense is more relevant than in the cosmological or paleological sense of the words. To sit and meditate on a place's history requires no schooling and no abstract visualization skills.
Places I've been that give me a feeling of deep time include:
Have you ever had such a feeling? Tell me where, and when, and the approximate conditions. I'm a traveller, and I hope to compile a list of "deep time" spots to visit in my travels. They are, in my experience, the most fulfilling destinations for the thinking tourist.
--rescued from nodeshell limbo, in the hopes that what I've written here is better than nothing