Doris Salcedo's crack, which snakes along the floor of the Turbine Hall, will be remembered alongside Damien Hirst's diamond skull as one of the most important works of art of the first decade of the 21st century - but not for reasons that the art world will be proud of.

It has nothing to do with the immaculate execution of the work, although this really is the most beautiful crack I have seen. Nor its realism - though the work even has its own splinter-cracks, which fortunately peter out before they reach the Tate bookshop. Nor its popular success - although last Saturday I admired the hordes following the path of the crevice, and the huddle of children at the far end trying to stick their hands under a wall of frosted glass, searching for the end of the illusion.

As this scene shows, the Tate crack is the contemporary art version of a High Concept Hollywood disaster movie and the crowds are all buying into the narrative, just as they do in the movies, despite the implausible plot.

Yet that is also not the reason why this is a work of art that is emblematic of our time. It has nothing to do with the neat correlation between "the line" - the simplest mark in a drawing - and the geological fissure, which a more pretentious art critic could surely write volumes on. Nor does an explanation lie in the continuity of the Turbine Hall commissions, which offer versions of the new populist symbolism in art.

Salcedo's seismic metaphor is another faked natural phenomenon like the misty sunset conjured up in Olafur Eliasson's Weather Project. The quake-line is also not a million miles from Carsten Holler's slides, which also asked us to think of the metaphors in a thrilling experience, that of whizzing down a slide at speed. Metaphors are the key but not the ones about colonialism, racism and social division the artist talks about in the gallery blurbs.

No, this is a crack that runs through the world's most popular museum of modern art. Just as Hirst's diamond-studded skull symbolises the pinnacle of vanity of the contemporary art bubble, the crack symbolises its imminent collapse.

In the past 10 years, prices paid for art have rocketed, often by a factor of 10, and an army of mediocre artists have been hyped beyond all reason. Last week, Sotheby's share price dropped 37 per cent after an unsuccessful modern art auction.

But the quake has only just started - it'll measure 12 on the Gerhard Richter scale - and the earth is set to swallow up some of the most famous names and sacred tenets of contemporary art.