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It seems never to happen. Assiduous collecting up cliff faces yields zigzags, minor oscillations, and the very occasional slight accumulation of change over millions of years, at a rate too slow to really account for all the prodigious change that has occurred in evolutionary history. When we do see the introduction of evolutionary novelty, it usually shows up with a bang, and often with no firm evidence that the organisms did not evolve elsewhere! Evolution cannot forever be going on someplace else. Yet that's how the fossil record has struck many a forlorn paleontologist looking to learn something about evolution.
Dating of the humin fraction of soil organic matter and its comparison with 14 C ages of fossil charcoal. The radiocarbon dating of the soil organic matter SOM is a polemic subject, due mainly to the complexity of the formation of the soils and to the variable contamination from several sources. Soil samples from 4 different Brazilian localities were submitted to physical and chemical pre-treatment for the extraction of humin fraction, which is the most stable organic compound and theoretically the oldest and representative of the age of the SOM. The radiocarbon dating obtained from the total SOM and their humin fractions are compared to the 14 C ages from buried charcoals at similar depths. Thus, the ages on humin fractions could be assumed as the minimum ages for the associated soils, while the results obtained on total SOM, even at depths until cm, exhibit pronounced contamination effect by modern carbon, rejuvenating their ages. As amostragens foram feitas em trincheiras de aproximadamente cm x cm x cm de profundidade.