That's right--deserted. There were no signs of any remains of living things. They'd all simply packed up and left, leaving everything behind.
Dating by the radiocarbon method was useless. Some of the carbon compounds in the various artifacts showed a faint trace of radiocarbon, others showed none. But since the method depends on a knowledge of the amount of nitrogen in the atmosphere of the planet of origin, the rate of bombardment of that atmosphere by high-velocity particles, and several other factors, the information on the radioactivity of the specimens meant nothing. There was also the likelihood that the carbon in the various polymer resins came from oil or coal, and fossil carbon is useless for radio-dating.
Nor did any of the more modern methods show any greater success.
It had taken Man centuries of careful comparison and cross-checking to read the evolutionary history written in the depths of his own planet's crust--t