As Brin himself writes in his unusual, and interesting, afterword, 50-year extrapolations are a difficult business; the future has to be identifiable, but also sufficiently different in understandable ways to be worthy of the genre. Earth is not only a spectacularly readable novel. It gets things "right," in the sense that the extrapolations are plausible (some might say "conservative"), the science (even the fictional "cavitronics") seems, to this layman, sound, the social milieux are eminently reasonable and closely observed. Importantly for this work, Brin more than a decade ago had a clear picture of the internet's potential power, and the web is here a central character. So too is Earth itself, in many guises--in fact, the novel can double as a delightful tutorial on various "green" topics. Moreover, Brin's theme of "competition and cooperation" as the engine of evolution and of complex emergent behaviors, human and otherwise, is brilliantly worked throughout the narrative. (And I've said nothing about the lucidly wrought, believable characters that thickly inhabit this long, ambitious, and carefully plotted work.) Some readers may complain the climax contains a touch of deus ex machina, but, in the story's context, it all works. Indeed, at the conclusion, you feel "everything fits, everything matters, everything affects everything else." Bravo, bravo, bravo.