Cambrian-Ordovician Extinction

During the Cambrian period, life flourished. The Edicaran life had remained largely unchanged for millions of years, but in the Cambrian it suddenly diversified and evolved into endless new forms. Exotic crustaceans and trilobites became the dominant life in their huge numbers and variety. Shellfish and giant aquatic arthropods, similar to insects, filled the seas. These creatures had rigid exoskeletons which left a bounty of fossils for us to study. Life flourished until, rather suddenly in geological terms, over 40% of all species suddenly became extinct 488 million years ago. Those that remained survived poorly at best due to some harsh change in the environment. What this change was we do not know. One theory is that a glaciation occurred, the coldest part of an ice age. We have been enjoying an interglacial period, the warmest part of an ice age, for the past eleven thousand years. An extreme change in temperature can easily cause the extinction of a huge amount of life. This extinction event marked the border between the Cambrian and Ordovician periods.

End-Ediacaran Extinction

During the Ediacaran period, complex life had begun to take form for the first time on Earth. Tiny bacteria had evolved into the more complex and specialized Eukaryotes, some of which grouped together to increase their chances of finding food and avoiding becoming food. Most of these odd creatures did not leave a record because they had no skeletons; they were soft and tended to rot when they died rather than fossilize. Only in peculiar circumstances could fossils form, such as a creature lying on soft mud which suddenly hardened and left an imprint. These few fossils tell us of seas full of strange and alien creatures who resembled modern worms, sponges, and jellies. However, these creatures were dependent upon oxygen, as are we. The oxygen levels began to fall and world-wide extinctions occurred 542 million years ago. Over 50% of all species died. The huge numbers of dead creatures decomposed and make up some of today’s fossil fuels. The exact cause of the lowering oxygen levels is unknown, however, this mass extinction made room for the Cambrian explosion, a sudden diversifying of complex creatures beyond mere worms.

Genetic Evidence of Geographical Groups among Neanderthals

The Neanderthals are a well-distinguished Middle Pleistocene population which inhabited a vast geographical area extending from Europe to western Asia and the Middle East. Since the 1950s paleoanthropological studies have suggested variability in this group. Different sub-groups have been identified in western Europe, in southern Europe and in the Middle East. On the other hand, since 1997, research has been published in paleogenetics, carried out on 15 mtDNA sequences from 12 Neanderthals. In this paper we used a new methodology derived from different bioinformatic models based on data from genetics, demography and paleoanthropology. The adequacy of each model was measured by comparisons between simulated results (obtained by BayesianSSC software) and those estimated from nucleotide sequences (obtained by DNAsp4 software). The conclusions of this study are consistent with existing paleoanthropological research and show that Neanderthals can be divided into at least three groups: one in western Europe, a second in the Southern area and a third in western Asia. Moreover, it seems from our results that the size of the Neanderthal population was not constant and that some migration occurred among the demes.