After Lucas returned to the camp, his life kept a certain rhythm and years passed. He knew it had been more than a year, but he would need more information to determine how long of a time he had spent seeing gray aliens, yellow landscape, and other beings that would be weird on Earth.
Most of the time that had passed had been spent outside of the front line camp.
He met others outside, but nobody had been lucky to live after meeting him. Not the Garsans either. He had had them as his specimens once, and he found how they were inside.
Cannon fodders had died, but more had come from the back line.
During that time, he managed to confirm that the hard jelly like rock he found on his first exploration was part of the resources that the Garsans wanted.
But he also confirmed his theory. The Garsans didn't attach much importance to what they could not use. So they might have other less important uses for the earth's attuned resources.