500:1?
"Five hundred tons of clear white crystal can be converted into one ton of red crystal?"
"Yes." The creature nodded, "But even so, Earth is still currently the first planet they've discovered in outer space that has the raw materials to produce their Source of Life. Based on the deposits they have already identified, full extraction could at least allow their species to continue for tens of thousands of years."
Tens of thousands of years...
Sounds like a lot, but for the continuation of a species, it's very short.
The ancestors of humans, Homo sapiens, have existed for 250,000 years, and tracing further back to ancient apes, it would be even longer.
In the long river of Earth's billions of years of life evolution, ten thousand years is just a moment.
Not to mention that this group of alien invaders has already explored space for twenty thousand years.
