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Large Life Forms May Have Evolved on Land

 
 
Reply Thu 13 Dec, 2012 12:26 pm
Wednesday, December 12, 2012
Cartoonists have found many clever ways to depict the conventional wisdom that complex life evolved in the sea and then crawled up onto land. But a provocative new study suggests that the procession might be drawn in the wrong direction. The earliest large life forms may have appeared on land long before the oceans filled with creatures that swam and crawled and burrowed in the mud.

This story is told from fossils that date from before an extraordinary period in Earth history, called the Cambrian explosion, about 530 million years ago. That's when complex life suddenly burst forth and filled the seas with a panoply of life forms.

Paleontologists have found fossil evidence for a scattering of fossil animals that predate that historic moment. These mysterious organisms are called Ediacarans.

Many scientists have assumed Ediacarans were predecessors of jellyfish, worms and other invertebrates. But Greg Retallack at the University of Oregon says he always had his doubts.

Retallack has been building the case that Ediacarans weren't in fact animals, but actually more like fungi or lichens. And if that idea weren't enough of a departure from standard theory, he now argues in a paper in the journal Nature that Ediacarans weren't even living in the sea, as everyone has assumed. He says he has reanalyzed some Australian rock where they're found and concluded that it's ancient soil, not marine mud.

These early life forms were landlubbers.

"What I'm saying for the Ediacaran is that the big [life] forms were on land and life was actually quite a bit simpler in the ocean," Retallack says.

So does that suggest life evolved on land and moved into the ocean?

"Yes, in a nutshell," he says.

This is an audacious idea. But Retallack is not alone in entertaining this possibility.

Paul Knauth at Arizona State University has been pondering this same possibility.

"I don't have any problem with early evolution being primarily on land," says Knauth, a professor in the School of Earth and Space Exploration at Arizona State University. "I think you can make a pretty good argument for that, and that it came into the sea later. It's kind of a radical idea, but the fact is we don't know."

Knauth says it could help explain why the Cambrian explosion appears to be so rapid. It's possible these many life forms gradually evolved on the land and then made a quick dash to the sea.

And, he adds, "that means that the Earth was not a barren land surface until about 500 million years ago, as a lot of people have speculated."

The new analysis of the Ediacaran fossils is at least a hint that this could be right. But of course if you're a scientist making an extraordinary claim, you need to back it up with extraordinary evidence.

"To me the evidence is not a slam-dunk," says Shuhai Xiao, at Virginia Tech.

He argues, among other things, that the same Ediacaran species found in what is arguably soil is also found in deposits that he says were ocean sediments.

That would imply that the same species would be able to live both on dry land and under a salty ocean. Xiao finds that unlikely. "It's pretty hard for the same species to be able to live in both environments."

So he is not convinced that Retallack is really looking at fossils in terrestrial soil. And so begins a sharp academic debate.

Xiao is far from alone in his skepticism. The current ideas have many defenders. Retallack seems to relish the controversy. He knows what he's in for.

"The idea that Ediacaran fossils were marine invertebrates is so deeply entrenched, it's in all the textbooks," he says. When someone (namely him) comes along and says that's not so, "it's going to be treated like a death in the family. It's going to go through all the phases of grief, starting with denial."

It remains to be seen whether the story ends with acceptance of Retallack's provocative proposal.

Copyright 2012 National Public Radio. To see more, visit http://www.npr.org/.
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Type: Discussion • Score: 8 • Views: 2,232 • Replies: 16

 
rosborne979
 
  1  
Reply Thu 13 Dec, 2012 03:03 pm
@edgarblythe,
The idea that Ediacarans evolved on land seems pretty unlikely to me. He needs better evidence than simply saying that the fossil substrait looks like soil instead of mud. That seems like a slim distinction from 500 Million years away.
edgarblythe
 
  1  
Reply Thu 13 Dec, 2012 03:40 pm
@rosborne979,
The land theory seems wrong to me also, but it's out there, so I thought I would see if anybody here wants to pick at it.
0 Replies
 
farmerman
 
  1  
Reply Thu 13 Dec, 2012 03:49 pm
@rosborne979,
Ediacaran life forms are those fossils from the Ediacara Period of the LAte Pre CAmbrian, not the CAmbrian. I think this is some reporters jiggering of the Geo Time scale.
The Ediacaran is the sedimentary unit that starts at the end of theCryogenian and terminates at theBasal Cambrian.
Its "Type section is the Ediacara Hills of AUstralia (Unified Nomenclature calls this period the Vendian

Many of the Pre CAmbrian life forms,(including some of the Ediacara assemblages) clearly were water dwellers because they left molds and casts in silt deposits that show water scouring.AND, some are also found in a segment of Ediacara Hills that are limey shales (Limestone rocks are all water formed, even cave deposits)
Joe Nation
 
  1  
Reply Thu 13 Dec, 2012 04:52 pm
This makes sense to this uneducated (very) mind. If I remember correctly the largest living thing on Earth is a mushroom/fungus somewhere in the Northwest of the USA?

I am fascinated by primitive life forms - prokaryotes, archaea(great Scrabble word) and Eukaryotes (that's us).

Why wouldn't it be possible for life to have evolved both in and on the soils of the Earth and in the depths of a salty sea?

Joe( so cool, Thanks Edgar)Nation

0 Replies
 
djjd62
 
  3  
Reply Thu 13 Dec, 2012 04:58 pm
as a wise man once said, it's better to have evolved and lost, than never to have evolved at all
0 Replies
 
hingehead
 
  1  
Reply Thu 13 Dec, 2012 05:56 pm
Don't know enough to have an opinion but thanks for sharing the article and your thoughts.
0 Replies
 
Lustig Andrei
 
  1  
Reply Thu 13 Dec, 2012 06:12 pm
What hingehead said.
0 Replies
 
rosborne979
 
  2  
Reply Thu 13 Dec, 2012 09:13 pm
@farmerman,
I thought Stromatolites were pretty much the first life form to leave a solid mark in the fossil record. Those were tidal bacteria colonies that formed their own little block of "land" to live on.

Given such a scenario as a starting point it might be difficult to say whether such a thing evolved on land or in the sea.
cicerone imposter
 
  1  
Reply Thu 13 Dec, 2012 09:15 pm
@rosborne979,
My wild guess is that life forms began in the seas or water.
rosborne979
 
  1  
Reply Thu 13 Dec, 2012 09:19 pm
@cicerone imposter,
cicerone imposter wrote:

My wild guess is that life forms began in the seas or water.
You're really going out on a limb there CI.
cicerone imposter
 
  1  
Reply Thu 13 Dec, 2012 09:40 pm
@rosborne979,
I don't think so. The exploration on Mars begins with trying to find water, the essential ingredient for life - as we know it. Other chemical elements may support life forms, but we humans do not know the what and how.
0 Replies
 
Setanta
 
  1  
Reply Fri 14 Dec, 2012 02:52 am
Clay . . . it all began in clay tubes.
0 Replies
 
farmerman
 
  2  
Reply Fri 14 Dec, 2012 04:13 am
@rosborne979,
stromatolites were evidence of blue-green algae forms and they were definately water associated because they show tidal "rings"
Theres on fossil from the Ediacara fauna from Western Ontario named Microdictyon which hadda been an anmal . look at the one below and tell me this is a plant.
Microdictyon was found in layers that were sands and shales deposited in streams so they been a land based critter.
Only a mother could love this guy.


http://y11evolution.wikispaces.com/file/view/Microdictyon.jpg/30715697/Microdictyon.jpg

Also, as I stated in my thread about the "Cambrian Explosion not being so explosive" there have been some recent finds in places of Pre Cambrian rocks from around the world that cast doubt on the explosive nature of the lower Cambrian.
from the Vindhya mountains (area north of Bhopal India) are several units from the Cryogenian into the Ediacara (pronounced EE Dee-(Yak)'-ron), that contain some really early forms of sea pens like Dicksonia and a really interestin critter that looks like a cross between a trilobite and an annelid. This one was called Spriggina and he is depicted below in the rendering from a recent Paleo article that I clipped from Wikimedia

http://upload.wikimedia.org/wikipedia/commons/thumb/4/4e/Spriggina_Floundensi_4.png/250px-Spriggina_Floundensi_4.png

farmerman
 
  1  
Reply Sat 15 Dec, 2012 05:49 am
@farmerman,
Actually, the Spriggina isnt a rendering, its really a photo of the fossil cast so its even more compelling that these guys were already on the way to hard shells in the Cryogenian (just before Ediacaran Times)
0 Replies
 
hingehead
 
  2  
Reply Sun 16 Dec, 2012 05:51 pm
@farmerman,
Hey FM, pardon me while I pick your brain

Are the blue thingies on this dude proto shells?
http://y11evolution.wikispaces.com/file/view/Microdictyon.jpg/30715697/Microdictyon.jpg
farmerman
 
  1  
Reply Sun 16 Dec, 2012 09:47 pm
@hingehead,
Thats a great point. The guys who first picked these things out of the rock in Western Ontario compared them to their "descendant forms" {named Asyheaia} in the Burgess Shale of Western Canada and found that the "blue dots " could have been some form of chitenous material. I was waiting for some follow-on articles about that but the guys musta gotten bored .
0 Replies
 
 

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