“A prior indigenous technological species might have arisen on ancient Earth or another body, such as a pre-greenhouse Venus or a wet Mars,” he wrote. ... Earth’s plate tectonics would effectively have “erased” the traces of a civilization that lived billions of years ago. Venus is in the grip of a severe greenhouse effect and also undergoes similar “resurfacing” that would scour it clean of artifacts. This leaves just a handful of places where archaeologists might find traces of a lost extraterrestrial civilization. “Remaining indigenous technosignatures might be expected to be extremely old, limiting the places they might still be...