independence day - How do the aliens use the Earth molten core to grow their technology?

The big sphere alien ship said that the Bad Guy aliens were trying to suck out Earth's molten core, to refuel their ship and "grow their technology".

I get how you can hand-wave using it to refuel.

But how can sucking out Earth's liquid core "grow their technology"?

_{I'm only looking for in-universe answers, preferably based in canon (the only rational explanation I myself can come up with is, you need more energy to upgrade your tech, not just better designs/science/engineering to come up with the upgrade ideas)}

Answer

The actual mechanism by which new ships are "grown" remains a mystery, but apparently it involves sucking up the liquid hot magma and turning it into baby motherships that can then be sent off to find new planetary systems to conquer.

“Correct,” it said. “A harvester ship conquered our planet and sucked out its molten core.” As it spoke it projected a hologram to illustrate. The massive vessel latched onto the planet and began to grow the same kinds of vine-like structures that were now enveloping the east coast of the United States. “They use planetary cores to refuel their ships and grow their technology. They have done this to thousands of species. They are Armageddon. The end of everything.” The hologram showed a smaller ship budding from the hull of the harvester, and detaching. It was an exact copy of the mother ship they had destroyed during the War of ’96.

So that was just a baby, David thought. One of probably thousands sent out into the universe to find the next feeding ground. He’d seen the growth of their technology on the level of individual organisms, but it was another thing to observe it at such a massive scale. The combination of biotechnology and advanced materials science was both intoxicating—because of the possibilities—and terrifying, because of the race that possessed it.

_{^{Independence Day: Resurgence - A Novel}}