Selective preservation hypothesis

Despite these advances, our knowledge of the details of coal formation remains quite sketchy. For example, we do not yet have a full knowledge of the biopolymers from plants that contribute to coal formation. Furthermore, while the selective preservation hypothesis provides the basis outlines of coal formation and organic geochemistry. 

The problem of foremost interest in future studies should be to ascertain whether operationally defined humin contains significant amounts of clay-humic acid complexes and to determine the genetic relationship between humic acids and humin. Another problem would be to define structurally the paraffinic components of humin and to ascertain whether they are truly biomolecules or are rapidly formed products of decomposition of vegetal matter. Finally, the hypothesis of selective preservation should be tested in other environments. 

The first step to test this hypothesis is the division of the dataset into a training and a test dataset. Two-thirds (3685 compounds) of the entire dataset were assigned to the training dataset and the remaining third (1828 compounds) to the test dataset by a random selection with the restriction that the ratio of hits to non-hits in the entire dataset is preserved in both the training and test dataset. 

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