From R&D magazine on-line
LINK to Arizona State Universite website on work

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At night the stars put on a show for free (Carole King)

One Earth, One Sky - IYA 2009
All moderation in purple

That is wierd. I was under the impression that plants first started coming onto land in the Silurian, I think. I would think that if there was that much plant life on the land, it should have been fairly obvious

The talk is of squishy prevascular plants of a type that wouldn't leave many fossils: slimy stuff, not ferns and liverworts.

http://www.scientificblogging.com/ne...carbonates_101

http://www.nature.com/news/2009/0907...l/460161a.html

I missed the non- in non-vascular. That changes things a bit.

Liverworts and mosses aren't slimy, and neither are vascular.

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If they are correct then either the "primitive ground huggers" were resistant to ultra violet or an ozone shield had been established by that time.

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(By the way, I hate it that so many papers in the areas of planetary science and geology are not easily available to the dreaded "non-subscribers". It is like they are screaming at me: "YOU CAN'T HANDLE THE TRUTH". Good, I feel better now.)

"Quaerendo inventis"

dogs and cats

That's what I thought: that the spread of life to land was only possible once a protective ozone layer had been established around 500 mya.

Regarding the Cambrian expolsion, was it not that a tipping point of sophistication had been reached whereafter animals tended to have skeletons that could form fossils?

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Yonder is Dubhe seen on Earth tonight as it was in the days of Grover Cleveland's presidency whereas this way is Deneb seen as it was in the lifetime of Muhammed . If one somehow travelled to Deneb at very close to c then whenever you looked back you'd measure Earth as closer to you than the distance you would simultaneously measure between Earth and Dubhe.

Not weird - the Arizona SU and UC Riverside scientists have just independently discovered Neoproterozoic stromatolitic algae ...

... but they still haven't heard of Ediacaran fauna ...

... the Archaean-Proterozoic transition seems to have escaped them, too ...

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Where does this come from?

yes - the widespread emergence of animals with hard parts, which are more easily fossilised ...

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Many "popular" books and even some textbooks have made similar statements, albeit it is probably dated material by now.

Give us your thoughts, please. (seriously)

John

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(By the way, I hate it that so many papers in the areas of planetary science and geology are not easily available to the dreaded "non-subscribers". It is like they are screaming at me: "YOU CAN'T HANDLE THE TRUTH". Good, I feel better now.)

"Quaerendo inventis"

dogs and cats

OK - fair enough ...
I have some outdated textbooks and reference books myself - excellent resources for historical background, etc, but not always reliable for conclusions in the light of later information ...

Well, AndrewJ's statement raises two issues:

1 - the timing of the establishment of the ozone layer; and
2 - whether the ozone layer (or even atmospheric oxygen) was the critical factor in the timing of the emergence of land-based life ...


but neither really address Swift's OP issue - "a possible trigger for the Cambrian Explosion" - which also has multiple discussion paths:

1 - the merits or otherwise of the linked article and associated study;
2 - the historical and contemporary importance of the Cambrian Explosion within the broader evolutionary trends;
3 - possible triggers for mass speciation events ...


So, I'm inclined to wait for Swift to clarify the OP intent or desired direction ...
rather than find myself hauled over hot coals for hijacking ...

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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.

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At night the stars put on a show for free (Carole King)

One Earth, One Sky - IYA 2009
All moderation in purple

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?").

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?

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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Yonder is Dubhe seen on Earth tonight as it was in the days of Grover Cleveland's presidency whereas this way is Deneb seen as it was in the lifetime of Muhammed . If one somehow travelled to Deneb at very close to c then whenever you looked back you'd measure Earth as closer to you than the distance you would simultaneously measure between Earth and Dubhe.

Thanks for that ...
I'll bring some tiger prawns (giant striped "shrimps") and beer ...

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 ...

*from memory, up to a billion years or more ...

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

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) ...

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That's interesting you should mention this, as during lunch I watched a History Chanel (I think) program on this effect. Supposedly the Earth was either nearly or entirely frozen during two or three periods in its past, either delaying or preventing the early establishment of multicellular life, but also as recently as 850 to 635 mya, during the Cryogenian period, during which the Sturtian and Marinoan glaciations occurred, the greatest ice ages known for Earth.

Of course we've had ice age temperatures considerably warmer than today, including 400 tya, 325 tya, 245 tya, and 120 tya. Beyond that, the ice core samples are unavailable, but other means, such as compilations of oxygen isotope measurements on benthic foraminifera strongly indicate that the Earth was much warmer throughout most of its history (2 to 12 deg C, mean around 6 deg C) than it is today.

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"Toward no crimes have men shown themselves so cold- bloodedly cruel as in punishing differences of belief." - James Russell Lowell

thanks mugs -
you triggered a self-correction (ie, shown where I've made an error based on bad memory ... again ... )

I'd confused the tillite formation ages (790 and 620) and had 690* in my head - this is well before the Marinoan, and well after the Sturtian; 700 Ma BP is roughly halfway between the peaks - ie, in the middle of the Cryogenian ...

which makes this:
also incorrect by roughly 75 Ma or so ...

all of which throws AndrewJ's question -
wide open and back into the mix for speculation and discussion ...



*thinking about the 490 C-O transition probably didn't help -
which I'd already confused by losing the Ordovician altogether -
sheesh! ... I need a better brand of coffee!

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