The foam began washing up on our shores two years ago. At first, it was sparse, resembled barely beaten egg whites, and most of us paid it scant attention. Because it posed no immediate threat, we relegated it to “scientific interest.” Over time, however, as it persisted, flowed and thickened into the consistency of properly steamed cappuccino froth, stories started appearing in the news: online, then on television. We traced its origins to deep within the Marianas Trench. But foam is boring, even as it subtly changes hue from ghostly white to green tea. Thus the first images of the foam most of us remember were mechanical, of urban plows pushing it back into the sea. That worked, for a while. But the foam inevitably returned, subtly thicker, greener and more expansive than before. By the time the plows ceased their effectiveness, we had already identified the asteroid (“Isaacasimov”) but had not yet made the connection. The foam, albeit having covered much of our coastline, remained more of a nuisance than a threat, for it did nothing. As Earth worked to track the asteroid, then scrambled to destroy it, the foam crept silently inland. As you may be able to deduce, we were successful in neutralizing the asteroid. The world watched united as our international mission broke the asteroid apart and diverted its larger chunks safely away from our planet. We expected the atmosphere to deal with the resulting debris, to watch the pieces burn as they descended, but our expectations proved incorrect. Instead of a display of shooting stars we witnessed a rain of cosmic dust. The atmosphere proved porous. Most grains fell upon the dry earth, but some landed in the now luminous green foam. Protected, they sprouted as seeds. Fertilized, they grew. There was an elegance to it: ancient nutrients from deep within the Earth and life from outer space. The resulting organisms, alien in the true sense of the word, were impervious to our weapons and excreted tiny spore-like particles as they matured. Within weeks, our skies were so polluted we could barely see the sun. We choked, and our immune systems reacted: we began foaming. Like our planet, our bodies betrayed us, and the particles took up residence in our moist and fertile viscera. They fed on us to breed. Once infected, an individual had only days left, but as a species we adapted, segregated and furiously engineered. I am one of the final survivors and personally witnessed the completion of the wormhole generator, via which I shall within the hour send this, my final communique, into an unknown past. Or should I say your present. But I, too, am foaming now, and my fate has already been sealed. I am by nature a pessimist, but if my pessimism is misplaced, heed my warning: Beware the foam!