When two or more elements combine in definite proportions naturally on Earth, what is created?

substance formed by the chemical combination of two or more elements in definite proportions (a thing that is composed of two or more separate elements; a mixture.)

The law of multiple proportions states that if two elements form more than one compound between them, the masses of one element combined with a fixed mass of the second element form in ratios of small integers. Consider two separate compounds are formed by only carbon and oxygen.