we are currently learning about radioactivity and i have become curious of how these heavier elements came to earth in the first place? From what i understand, the lighter elements are formed by fusion in stars, but even so, how could these lighter elements reach us when the stars are so far away? I could see perhaps some of the elements reaching us as dust or something, but how did enough of it reach us to allow for start of life? I mean carbon for example is absolutely essential to life, so we would need extremely large amount of it for the first living cells to begin synthesizing themselves. Also, according to current model, the early earth was big glob of lava and whatnot, so all of the chemicals must have been mixing around all together, so then why today we have more or less even "deposits" of certain chemicals, like uranium? I mean if in liquid form the earth was all mixed up, then how come when it cooled, it became more ordered in terms of chemical composition?