In 01995 (they use the extra digit to protect against the deca-millennium bug), the clock's creator, Daniel Hillis, wrote:
I think of the oak beams in the ceiling of College Hall at New College, Oxford. Last century, when the beams needed replacing, carpenters used oak trees that had been planted in 1386 when the dining hall was first built. The 14th-century builder had planted the trees in anticipation of the time, hundreds of years in the future, when the beams would need replacing. Did the carpenters plant new trees to replace the beams again a few hundred years from now?
I want to build a clock that ticks once a year. The century hand advances once every one hundred years, and the cuckoo comes out on the millennium. I want the cuckoo to come out every millennium for the next 10,000 years. If I hurry I should finish the clock in time to see the cuckoo come out for the first time.
The first prototype was indeed ready on December 31, 1999. Since then, the Long Now organization has purchased some land in Nevada for the site of the final, larger version of the 10,000 year clock. Design principles (transparency, durability, low-tech) and schematics are available on their web page.
What's the motivation? Jonas Salk, right before he died, challenged the clock builder to figure out what, exactly, he was trying to preserve. In response, he wrote:
I know I am a part of a story that starts long before I can remember and continues long beyond when anyone will remember me. I sense that I am alive at a time of important change, and I feel a responsibility to make sure that the change comes out well. I plant my acorns knowing that I will never live to harvest the oaks.
I guess, ultimately, it's awe-inspiring, but not moving. I'm reminded of Ypres, where, every evening, the Fire Brigade has been sounding The Last Post in honor of a solider who died on that Great War battleground. They've been at it since 1928, and, since about 90,000 died at Ypres, the brigade will keep playing, daily, well into the 22nd century.
Their acts may not generate the mind-blowing plans for the 10,000 Year Clock, but the Ypres brigade moves me in a way the Clock fails to. Even the Oxford tree-planting is more striking, because it's long-term planning with purpose. However, the Long Now's Rosetta project and library perservation goals may yet give future Clock visitors a reason to care about the culture that built it.