Also known as the Avalon and Cambrian Explosions, those rapid diversification events have been lacking a satisfactory explanation so far. Some earlier work postulated this was just an artifact of the fossil record and there was no 'smoking gun'.
As far as the Cambrian Explosion is concerned, the sudden appearance and proliferation of shelled macrobiota (in particular those using calcium carbonate to make their protective shell or exoskeleton) was a strong hint that the oxygenation of seawater had increased a lot since the organism has to extract it in order to secrete CaCO3.
Elaborate trace fossils present below (and therefore before) shelled macrofossils indicate that some soft-bodied arthropods were present. Presumably they lacked enough oxygen to secrete much calcium carbonate. There are so-called "small shelly fossils" just above the first complex trace fossils but their shells are predominantly chitinophosphatic and the animals are of very small size. Diminutive fauna (dwarfism) is often associated with episodes of oceanic anoxia (for example some Cretaceous events) and can be a good indicator of depleted oxygen levels.
Gonna be fun to see if future data corroborates this hypothesis.
http://www.astrobio.net/news/m...thread&order=0&thold=0
http://www.astrobio.net/news/m...&file=article&sid=2580
As far as the Cambrian Explosion is concerned, the sudden appearance and proliferation of shelled macrobiota (in particular those using calcium carbonate to make their protective shell or exoskeleton) was a strong hint that the oxygenation of seawater had increased a lot since the organism has to extract it in order to secrete CaCO3.
Elaborate trace fossils present below (and therefore before) shelled macrofossils indicate that some soft-bodied arthropods were present. Presumably they lacked enough oxygen to secrete much calcium carbonate. There are so-called "small shelly fossils" just above the first complex trace fossils but their shells are predominantly chitinophosphatic and the animals are of very small size. Diminutive fauna (dwarfism) is often associated with episodes of oceanic anoxia (for example some Cretaceous events) and can be a good indicator of depleted oxygen levels.
Gonna be fun to see if future data corroborates this hypothesis.
http://www.astrobio.net/news/m...thread&order=0&thold=0
http://www.astrobio.net/news/m...&file=article&sid=2580
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