For millennia local time, the technologically-advanced Xrbgol civilization had been sending probes throughout its galaxy, looking for somebody – anybody – out there who showed signs of developing similar technologies and surviving the event. One such probe returned from a distant arm of the galaxy with evidence of proto-intelligent life forms on the third planet of a small yellow star with the uncouth local names of Sol or Sun. (They were slightly happier with names such as Helios.) Intrigued, the Xrbgol sent a second probe to the region. Several generations of Xrbgolia later, the probe returned – with news that the civilization had collapsed. Scientists assigned by their great-great-grandmothers to the Sol project gathered around the sentient probe to ask …
“Well, probe, what happened?”
The probe, a disk around four meters in diameter and perhaps a meter high, designed for speed, efficiency, and undetectability by lesser intelligences, opened a small circular hatch at the central crest of its dorsal surface. From the opening, a holographic presentation appeared, summarizing in a series of images what the probe had discovered. A disembodied voice narrated.
“As anticipated from the observations of the prior probe”, it intoned, “the civilization on the third planet from [sigh] Sol, with the even more unsatisfactory local name of Earth (the assembled scientists shuddered as if they had been unceremoniously dumped into a vat of untreated sewage) had been progressing. It had reached a sophisticated level of artisanal technologies, represented by such things as complex habitation buildings and sophisticated sailing ships, and was on the brink of achieving an industrial revolution. And then, it all came apart, due to a remarkable biological event.
“Legends of the bipedal inhabitants, which have regressed to small bands of mostly hunter-gatherers, speak of a time in which vegetation, in the form of large growths called “trees”, suddenly became able to consume animals. They became carnivores. Cross-sections of selected trees, achieved with difficulty even with our energy-beam tools, verified the legends by showing a layer within the trees that was saturated with calcium phosphate objects, interpreted as the bony skeletons of consumed animals. Different tree species evidently preyed on different animal species. In the example shown, the width of the tree ring is less than half of what it would have needed to be to hold the remains of the proto-intelligent species that was pursuing technological development; it could only have eaten much smaller prey.
“Just as inexplicable as the onset of carnivorous trees is its cessation, apparently after a single revolution of (gah!) Earth around (urk!) Sol. It is unclear how many direct casualties the bipedal inhabitants, called, sorry, humans (the assembled scientists groaned, a few of them retched), suffered. It must have been substantial, for the trees, as mentioned, developed a cylinder of calcium phosphate around their circumferences that was essentially continuous. But that by itself is insufficient to explain the societal collapse, given the fecundity that the species had previously shown in the face of deadly diseases and periodic episodes of famine and warfare.
“It must be understood that the trees had become a primary resource for fuel and building materials, critical for the prospects of technology development by this civilization. At a stroke, this material became unavailable. It could no longer be worked with available tools. It no longer could be burned with anything like the energy yield the tree material had previously had. Structures, especially ships, a prime mover of commerce and technology exchange, could no longer be either constructed or repaired. Weaponry for hunting and for conflict resolution could no longer be made; the tree material, I won’t utter the word used to name it (“Thank you!”, the scientists murmured), was no longer suitable in itself, and could no longer generate the heat needed for metalworking. The planet does contain large reserves of exploitable energy rock and tars, but they no longer had the means to explore and develop these resources.
“The trees won protection against what had become their most significant predator, and those predators are now no more than roving bands. There is, as a result, no prospect that this planet will develop advanced technology.”
The lead scientist moved to dismiss the gathering. “We can let them wallow in their (he spat) Earth. I suppose it’s as well that they collapsed before they achieved significant technological capacity. I don’t wish to contemplate what would have happened if they had. We already have examples aplenty, we don’t need any more. Especially not from them.”
The scientists left the room, shutting off the lights and closing the door. The probe sealed itself off and went to sleep, pending its next assignment, and hoping that it would be a little more savory.