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Originally Posted by Swift
My intent was only I thought people here might be interested in this item. Please, drag the thread in any direction you like and I'll save the hot coals for the barbecue.  |
Thanks for that ...
I'll bring some tiger prawns (giant striped "shrimps") and beer ...
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Originally Posted by AndrewJ
I really don't know, I feel as if I've heard it so many times I took it as given. Perhaps it's repeated as it is a simple explanation and the question "why did life move on to the land?" occurs to everybody (second only to "why did we come down from the trees?").
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Again ... fair enough ...
As far as I know, the question is still valid and not fully resolved -
and the period following the ~
490 Ma BP Cambrian-Silurian [ETA -Meant 420 Ordovician-Silurian; the 490 C-O was another mass extinction event entirely] boundary remains significant for land-based macrobiota (complex animals and plants); there was also something of a mass extinction to recover from ...
colonial photosynthetic microbiota (algae, "slimy green stains on/in rocks", "pond scum", etc) are thought to have been sub-aerial (intra-tidal and surface water catchments) for a bit* longer ...
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from memory, up to a billion years or more ...
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The text in the OP refers to "a massive greening of the planet by non-vascular plants, or primitive ground huggers...roughly 700 million years ago" that oxygenated the atmosphere and allowed more complex animals. "Primitive ground hugger" implies there was an intial partial move to the land before the main immigration. Is there an explanation for the move 700 mya?
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perhaps ...
700 Ma BP - the Earth was in a long "cool" era,
ETA: and many parts were starting to get a lot cooler; it marks the beginning of the second peak of glaciation (the Marinoan) ... the infamous "Snowball Earth" label was first applied to this period ... with ice accumulating on land, sea levels were falling; intra-tidal stromatolitic communities were drying out (hence widespread deposits of organic carbon) ...
ten million years later, things started warming up, and early Ediacarans moved into the neighbourhood ...
WRONG!!! Memory glitch - see post #17
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Interesting as such investigation is we may not need a definitive cause for the Cambrian Explosion. We have fossils of pre-Cambrian animals and evidence of pre-Cambrian predators. Perhaps the "explosion" was the reaching of a threshold allowing more morphological variety (including those features which are now fossils).
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The Ediacaran-Cambrian boundary poses some interesting puzzles -
the first mass extinction - mass speciation coupled event; was the cause of one also the trigger for the other?
The rise of atmospheric oxygen, and by extension the ozone layer, is an ongoing unresolved debate over interpretations of the geological evidence -
depending on who you read, you'll find answers ranging from pre-LCB (~4Ga BP) to post-Cambrian Explosion (~500Ma BP), with most settling somewhere around the Palaeoproterozoic (~2500Ma BP - ~1800Ma BP) ...