I had not been able to get out into the field for months, so on the first warm day of spring, I headed to a nearby outcrop of Ordovician rocks, one I had visited several times before and always yielded some interesting fossils. For hours I contentedly hammered away, stopping every once in a while to examine the surface of a slab to see what it contained. Trilobites were especially exciting. Bang! Bang! Clink! Clink? A glint of metal caught my eye. Initially, I thought it was one of the many pieces of trash dumped along the roadside. With a jolt, I realized it was deeply embedded in the rock. Meteorite!! Meteorites had been found in other Ordovician age rocks, so this was highly unusual, but not unique. Then I took a closer look. This was no meteor; it was a refined metal and was flat, not round. Spaceship!! I had found the first evidence of an alien visit to Earth! Fame, fortune, an appearance on the Late Show! Then I wake up.
This is a fantasy I have had for some time. As a fan of science fiction, I had long imagined an alien visit to our planet. But as a paleontologist, I also recognized that this visit could have taken place anytime during the last 4.5 billion years of Earth history. If they had visited during the first billion years, there may not have been anything living. For nearly two billion years after, only single celled archaea and bacteria. From 1.5 billion to 0.6 billion years ago, there would also have been single-celled eukaryotes. It was not until about 580 million years ago that would have been multicellular organisms to see and no animal life on land until probably 420 million years ago. And our own species did not exist until about 300,000 years ago. As for historical times, as Steve Gould put it, paraphrasing John McPhee, “Consider the Earth’s history as the old measure of the English yard, the distance from the King’s nose to the tip of his outstretched hand. One stroke of a nail file on his middle finger erases human history.” So, the odds of a random alien visit occurring in our lifetimes are not zero, but they are very small. On the other hand, that is a lot of time for extraterrestrial visitors to leave some trace of themselves behind. If they are anything like us, it would probably be in the form of trash.
This fantasy was recently revived by listening to a talk by Harvard professor of astronomy Avi Loeb and reading his book extraterrestrial: The First Sign of Intelligent Life Beyond Earth. In late 2017, the object dubbed ‘Oumuamua was discovered rapidly departing the solar system. Based on its trajectory, it became clear that its origin was from outside the solar system, the first extrasolar object ever discovered. That much is uncontroversial. But during the limited time it was observed, it was also clear that were some distinct oddities of the object, especially a slight deviation from its projected path. Loeb ably summarizes the limited evidence that is available and argues that they are consistent not only with an extrasolar object, but one that is artificial, perhaps a light sail. As a paleontologist, I am used to interpreting fossils based on the limited evidence that is preserved and coming up with interpretations that are consistent with the preponderance of the data, with the hope that future discoveries will allow additional testing of the idea. Although this way out of my expertise, my reaction to Loeb’s idea is similar: the evidence is consistent with the hypothesis of alien object, but that does not mean that some other hypothesis may turn out to be equally consistent (for example, https://news.agu.org/press-release/interstellar-object-oumuamua-is-likely-a-piece-of-a-pluto-like-planet/). Unfortunately, no further evidence on ‘Oumuamua will ever be found. As a scientist, I love the audacity of the idea (I was an “early adopter” of the Alvarez hypothesis). And my inner science fiction fan hopes Loeb is correct.
One section of Loeb’s book directly touches on my fantasy. In one place, he says “perhaps the easiest way for us to look for alien technology in our solar system…is to devise a method to detect it as it collides with Earth…If the object is bigger than a few meters, it could leave behind a remnant meteorite that … might yield the first tangible evidence of extraterrestrial technology.” (p. 141). What I am suggesting is that if they exist, such a meteorite could have fallen in a place where they survived the filtering effect of geological processes, waiting to be discovered by the intrepid geologist or paleontologist. I hope it is me.