Why is radiometric dating unreliable for dating rocks billions of years old?

Take your typical potassium-40 to argon-40, which is what they use to measure lava. They calculate that potassium-40 has a certain rate of decay, and here's the problem: you don't know how much potassium-40 and argon-40 were already in the original sample. Say you have 95% potassium-40 and 5% argon-40; you're going to conclude the rock's not very old, because the older the rock, the more argon-40 you find relative to potassium-40. But you need to know what that ratio was at the beginning, when the rock formed, to make any conclusion about the percentages a million years afterward. Knowing the decay rate only gives you part of what you need. You need what they call the parent-daughter ratio: the parent is potassium-40, the daughter is argon-40. Unless you know that ratio at the beginning, you don't know anything. That's why it's unreliable. And this can be proven. When Mount St. Helens erupted in Washington in 1980, lava poured out, and after a year they measured the potassium-argon decay ratio, and it said the eruption happened 2.5 million years ago, based on the same calculations they use to date other rocks, yet we know Mount St. Helens erupted 44 years ago. So something's off. When you hear these big numbers, it's all nonsense, and we have proof of it. It's all based on a theory that the universe has to be multi-billion years old. They assume that, and then every other theory, radiometry, paleontology, fossil formation, is built on that one idea. Now, uranium-238 has a half-life of 4.8 billion years, and everybody says that means the universe has to be at least that old. But a half-life is just when half the specimen decays. Carbon-14 has a half-life of 5,700 years and turns into nitrogen-14. But the half-life of uranium has nothing to do with how old the universe is. It only tells you what the half-life of uranium-238 is. God made some elements that by their nature are unstable, but whether that decay happens fast or slow tells you only about the element itself, how stable it is, not how long it's been around. That's what the evolutionists love. You're reading into it what you want to see, and what they want is long ages, because that gets us away from the six days of Genesis. The more years they tack on, the more time and chance they have to make man evolve by itself. It's not the knowledge; it's what you do with the data, how you connect the dots.