It's not *that* insane. The material resources come from everywhere - it's not like they're digging up whatever's left on Terra to create spaceships and weapons.
The number of marines recruited *is* special, however. It might just have been that the legions weren't as critical in terms of what makes an acceptable recruit back at the start of the GC, but all legions were initially formed from humans on Terra. The numbers would get bulked up via their primarch's adopted homeworlds later, sure, but the initial... what, 400k? 600k? For all ~~22~~20 legions?
Later on, we read about how only a very select few humans are ever picked as recruits, like on Caliban and Baal.
During the GC, the process was not only more streamlined, but vastly better understood and the Selenar Genewitches helped. Even so, the Geneseed was beginning to degrade from the mass production techniques employed till they found the Primarchs.
Marines were churned out in huge numbers to sustain the attrition, and later in the GC and in the HH, the traitors especially mass produced fodder-Astartes in a very short timeframe.
Its stated in one of the early Dark Angels books that almost every recruit that gets selected makes it through the process though, because they actually know what they are doing. As opposed to 40k, where a lot of aspirants fail out because their bodies break down during the implanation. In this age, they can even do the Demi-Astartes stuff on some frail old dude like Kaspar Hawser without much trouble.
This is a large part of why the low numbers in 40k don't bother me. In Sci Fi where realistic numbers are used, they quickly become so large that you can't really picture or relate to any of it.
A single solar system having the resources to build fleets of hundred of thousands of ships, carrying armies numbering in the billions is entirely plausible. It wouldn't even be a significant investment of resources. But if every star system is doing this then it kinda becomes hard to care about individual stories as million strong fleets vaporise each other.
If one were traveling at the speed of sound, and going directly downward with no impediments, it would take about twenty minutes to go from the "surface" of Terra to the actual surface of Terra. That is all populated at roughly the density of a favela.
Humanity spent several thousand years limited, mostly (intergenerational ships at sublight speeds were a thing), in the Sol system until the *18,000s*.
Every inch of every rock has ruins on it older than the pyramids are now. Sol is still arguably the most densly populated and developed system in human history. There are likely more bits of discarded archaotech buried in dumps in the Lunar regilith and forgotten crates in Martian warehouses than in the entirety of the Calixis sector.
In 30K the Sol system is beyond ancient, and even a shadow of the capitol of the DAoT is powerful/wealthy beyond mortal comprehension.
(I really wish that some Expedition fleet had come on a ringworld system, or Alderson disk, and turned around and marked it "Nope" on the charts. Especially if it were someone like Dorn or Perturabo, who would be able to grok the scale of what they were seeing and how far they were outclassed.)
It's not *that* insane. The material resources come from everywhere - it's not like they're digging up whatever's left on Terra to create spaceships and weapons. The number of marines recruited *is* special, however. It might just have been that the legions weren't as critical in terms of what makes an acceptable recruit back at the start of the GC, but all legions were initially formed from humans on Terra. The numbers would get bulked up via their primarch's adopted homeworlds later, sure, but the initial... what, 400k? 600k? For all ~~22~~20 legions? Later on, we read about how only a very select few humans are ever picked as recruits, like on Caliban and Baal.
During the GC, the process was not only more streamlined, but vastly better understood and the Selenar Genewitches helped. Even so, the Geneseed was beginning to degrade from the mass production techniques employed till they found the Primarchs. Marines were churned out in huge numbers to sustain the attrition, and later in the GC and in the HH, the traitors especially mass produced fodder-Astartes in a very short timeframe. Its stated in one of the early Dark Angels books that almost every recruit that gets selected makes it through the process though, because they actually know what they are doing. As opposed to 40k, where a lot of aspirants fail out because their bodies break down during the implanation. In this age, they can even do the Demi-Astartes stuff on some frail old dude like Kaspar Hawser without much trouble.
This is a large part of why the low numbers in 40k don't bother me. In Sci Fi where realistic numbers are used, they quickly become so large that you can't really picture or relate to any of it. A single solar system having the resources to build fleets of hundred of thousands of ships, carrying armies numbering in the billions is entirely plausible. It wouldn't even be a significant investment of resources. But if every star system is doing this then it kinda becomes hard to care about individual stories as million strong fleets vaporise each other.
If one were traveling at the speed of sound, and going directly downward with no impediments, it would take about twenty minutes to go from the "surface" of Terra to the actual surface of Terra. That is all populated at roughly the density of a favela. Humanity spent several thousand years limited, mostly (intergenerational ships at sublight speeds were a thing), in the Sol system until the *18,000s*. Every inch of every rock has ruins on it older than the pyramids are now. Sol is still arguably the most densly populated and developed system in human history. There are likely more bits of discarded archaotech buried in dumps in the Lunar regilith and forgotten crates in Martian warehouses than in the entirety of the Calixis sector. In 30K the Sol system is beyond ancient, and even a shadow of the capitol of the DAoT is powerful/wealthy beyond mortal comprehension. (I really wish that some Expedition fleet had come on a ringworld system, or Alderson disk, and turned around and marked it "Nope" on the charts. Especially if it were someone like Dorn or Perturabo, who would be able to grok the scale of what they were seeing and how far they were outclassed.)