Did Sea Life Arise Twice?

eldavojohn writes "Dr. Adam Maloof has found fossils of sea sponges in Australia from 650 million years ago. You might think this is no big deal unless you consider that sea sponges were thought to have arisen 520 million years ago. These fossils predate the oldest hard bodied fossils we have by a hundred million years. Dr. Maloof is now wondering if life might have arisen twice after the first attempt was quashed 635 million years ago: 'Since animals probably did not evolve twice, we are suddenly confronted with the question of how some relative of these reef-dwelling animals survived the Snowball Earth.' So how is it that life survived the Marinoan glaciation? The BBC has a video on the topic and Wikipedia has a time line of the Proterozoic Eon into the Paleozoic Era."

Comments

Life fills a space defined by its environment

[hessian]

Life creates itself to fit a niche, through a trial-and-error process called natural selection.

1. Does this mean life could arise twice, in similar form? Yes, and in fact there's evidence for parallel evolution:

http://www.sciencedaily.com/releases/2010/02/100225214757.htm

2. Does this mean that life on other planets arises identically or near-identically to our own, or that the origin of life on earth comes from elsewhere? Possibly:

http://en.wikipedia.org/wiki/Panspermia

Basically, life adapting to similar conditions in different areas would have a similar "blueprint" although possibly different DNA reflecting a different route to that end.

Re:Life fills a space defined by its environment

[mcgrew]

OK, since I took the two seconds necessary to RTFA, the summary's title is wrong. TFA specifically says NOT that life evolved twice, but that the date the Earth was inhabited was pushed back.

If correct, the finding would mean that animal life existed before the Marinoan glaciation - a global catastrophe known as 'Snowball Earth' when the entire planet was covered in ice.

Previously it was believed that animal life first emerged after the Snowball Earth event around 635million years ago.
Dr Maloof told The Times: 'No one was expecting that we would find animals that lived before the [Snowball Earth] ice age.
'Since animals probably did not evolve twice, we are suddenly confronted with the question of how some relative of these reef-dwelling animals survived the Snowball Earth.'

Now I have to read your links, at least the first one. But as to the second,
Does this mean that life on other planets arises identically or near-identically to our own, or that the origin of life on earth comes from elsewhere?

There is no proof at all that life exists anywhere else except on earth. When and if we find life elsewhere, than we can make conjecture about panspermia, until then it's just science fiction. Not even junk science.

Re:Life fills a space defined by its environment

[Anonymous Coward]

OK, since I took the two seconds necessary to RTFA, the summary's title is wrong. TFA specifically says NOT that life evolved twice, but that the date the Earth was inhabited was pushed back.

Where does the title say "evolved twice"?

Re:Life fills a space defined by its environment

[mangu]

the probability of life isn't equal to zero, and there are a ridiculous number of stars and planets

"Ridiculous number of planets" means nothing. For all we know the probability of life could be "ridiculously" small, so small indeed that multiplied by the total number of planets in the universe the product is still so small that life exists only on earth.

We have indications that this probability is very small. We have two examples of planets in our own stellar system that missed the habitable zone. Venus is so hot that complex molecules are unlikely to exist there. Mars is so cold that water cannot exist in liquid form. It has been conjectured that the moon was essential to the spontaneous creation of life on earth, because otherwise there wouldn't be tidal pools that concentrated the elements in the primitive sea.

Those are all conjectures, of course, and there may be counterpoints to them, but they are consistent with the hypothesis that life could be an extremely unlikely thing to happen in a planet. At this point the only sensible position is "we don't know" if life exists elsewhere.

Re:Throw away the Snowball.

[expatriot]

Don't trust Daily Mail interpretations of any thing scientific. Or non-scientific.

He was on the radio and said:

He did not consider dual evolution likely and would be surprised if anyone proposed it.

The dates were not certain, but they were much earlier than previously thought.

Earlier life existed, but only at single-cell level.

Heat was most likely provided by volcanic heating or hot water vents. (There are animals present now that have evolved to live in deep water near vents.)

Dating methods are accurate!

[G3ckoG33k]

Most dating methods that are used routinely are accurate; that is why they are used. Carbon 14 is typically NOT used for objects older than 45,000 years, when it becomes useless. For older objects, other methods are used.

http://en.wikipedia.org/wiki/Radiocarbon_dating

.

Re:Dating methods are accurate!

[Bowling Moses]

Whether or not you get similar numbers from different radiometric techniques depends on what the half life of the decaying compound is. Carbon-14 has a half life of 5,730 years, decaying into nitrogen-14. Uranium-235 decays to lead-107 through the actinium series with a half life of around 704 million years. Both methods are highly precise, with around about a percent uncertainty. For C-14, a percent is 57.3 years. For U-235 a percent is 7 million years. There will be negligible decay of U-235 in 57.3 years. There won't be any C-14 left in 7 million years. There is no reason to ever expect these two methods to agree on the age of something because of the difference in decay rate.

Re:Dating methods are accurate!

[Anonymous Coward]

"Less commonly, radiometric dating can be used, but that requires that an event (typically volcanic) reset the atomic clocks in the rocks in question to zero. Since pouring lava over a fossil tends to destroy it, radiometrically dateable fossils aren't all that common"

You underestimate how common volcanic ash and other volcanic rocks that bracket the age of fossils are. Ash beds (or their altered equivalents, such as bentonites or tonsteins) are quite common. When a volcano erupts it can toss the ash considerable distances, and eventually the ash rains out and gets deposited in the sediments containing the fossils. Sometimes individual ash beds can be correlated for hundreds to thousands of kilometres. Thus they can sometimes provide age constraints over a huge area. The main limitation is the money to do the dating methods and the patience required to hunt for and extract the relevant minerals from the ash (e.g., K-feldspar and zircons for K-Ar and U-Pb methods). Sometimes you extract the minerals and find that they've been too chemically altered to use for dating, which is frustrating, but all you need to do is find an appropriate layer above the fossil and one below and you have the age of the fossil constrained. Sometimes you just have to be persistent (e.g., if you can't extract unaltered feldspars for K-Ar, then try for zircons for U-Pb, which are rarer and the analysis costs more, but they are chemically more durable).

There are other situations where volcanic or intrusive rocks can constrain the age of fossils, albeit more widely spaced. For example, if a fossil is found in a sedimentary rock layer deposited above the eroded surface of a granite, then the sediments containing the fossil are younger than the granite. Radiometrically date the granite and the fossil must be younger than that age. An intrusive igneous rock injected into a sedimentary rock is younger than the deposition age of the sediments (you can't intrude into rock that isn't there yet!), and thus a radiometric date of the intrusive rock must be younger than the fossil. Again, you end up with older and younger brackets for the age of the fossil. Even if the brackets are going to be wider you do have an envelope.

In case of wiki-vandalism

[Anonymous Coward]

"Timeline of evolution" at 03:43, 16 August 2010

Note to Slashdot Editors: When used as references, Wikipedia links should be to a specific version of the article.

Title a bit off

[esocid]

It doesn't speculate that two similar life forms evolved twice. It only asks a question of how they survived glaciation. The molecular evidence pointed to an earlier evolutionary divergence for sponges, but no fossils were found until now.

The oldest known fossils of hard-bodied animals were two sea-dwelling organisms which lived around 550million years ago, called Namacalathus and Cloudina. But DNA evidence from sponges has suggested that their origins predate this. Marc Laflamme, of Yale University, said the earliest known sponge fossils were about 555million years old. He said: 'We had chemical and molecular evidence of fossils at this time but we weren't finding any real fossil specimens. 'What Adam's group was able to find was first evidence of true fossils of sponges at this time.'

By law of parsimony, the most likely explanation is that sponges arose once, and survived. While it isn't impossible that two similar organisms evolved from the same organism to fill a niche, it is tough to show evidence that two identically structured organisms arose twice, at different times. Most often when this happens, it happens at relatively close time intervals in physically separated areas, with simple changes. Seeing evidence to the contrary would be amazing, but in molecular evolution and probabilistic modeling, the more assumptions you make, the less robust the results will be, and so far all we have is/are fossils with identical structures.

Re:First link is trash

[esocid]

Here's a link to the original article, published yesterday. It's subscription based, which is why the OP didn't link to it. http://www.nature.com/ngeo/journal/vaop/ncurrent/full/ngeo934.html Maloof, A.C. et al. 2010. Possible animal-body fossils in pre-Marinoan limestones from South Australia. Nature Geoscience. Published online.

Abstract:

The Neoproterozoic era was punctuated by the Sturtian (about 710 million years ago) and Marinoan (about 635million years ago) intervals of glaciation. In South Australia, the rocks left behind by the glaciations are separated by a succession of limestones and shales, which were deposited at tropical latitudes. Here we describe millimetre- to centimetre-scale fossils from the Trezona Formation, which pre-dates the Marinoan glaciation. These weakly calcified fossils occur as anvil, wishbone, ring and perforated slab shapes and are contained within stromatolitic limestones. The Trezona Formation fossils pre-date the oldest known calcified fossils of this size by 90million years, and cannot be separated from the surrounding calcite matrix or imaged by traditional X-ray-based tomographic scanning methods. Instead, we have traced cross-sections of individual fossils by serially grinding and scanning each sample at a resolution of 50.8m. From these images we constructed three-dimensional digital models of the fossils. Our reconstructions show a population of ellipsoidal organisms without symmetry and with a network of interior canals that lead to circular apertures on the fossil surface. We suggest that several characteristics of these reef-dwelling fossils are best explained if the fossils are identified as sponge-grade metazoans.

It was peer reviewed, so I would suspect that their methods weren't trash.

Re:Evolution finally refuted

[golden age villain]

Stay here, other planets are populated by evolving robots!

How did they survive?

[Burnhard]

'Since animals probably did not evolve twice, we are suddenly confronted with the question of how some relative of these reef-dwelling animals survived the Snowball Earth.'

Forgive my trolling, but Dr. Maloof is an idiot. There are things called hydrothermal vents that certain species of sponge live around. So unless he thinks "Snowball Earth" involved the complete freezing of the oceans and, indeed, all other bodies of water, a hypothesis can easily be constructed to answer his question.

Re:Throw away the Snowball.

[vtcodger]

***Don't trust Daily Mail interpretations of any thing scientific. Or non-scientific.***

I think you've nailed it. The article appears to be horribly garbled. FWIW, the earliest bacterial fossils are 3.8 billion years old. Fossilized microbial mats are quite common back for hundreds of millions of years before the first animals appeared. Some complex fossils -- probably multicellular colonial assembleges (but maybe not 'animals') of one sort or another -- Chuaria, Tawuia, Grypania --go back a very long time. I think that the oldest previously well established animals are whatever created tracks thru the sediments of the fossil assemblege at Fortune Head Newfoundland 595 million years ago.

Re:We all know about the scientific method.

[mangu]

we do not have any way to verify the decay rate unaffected by cosmic radiation using the classic scientific method

Yes we do. There are nuclides with half lives of billions of years. How do we know? Get a pure sample of some isotope and measure how much of it has decayed after a known period. If after one year one billionth of the nuclei has decayed we can calculate that after a billion years 63.2% of the atoms will have decayed.

We know which nuclides come from which ones. We have a well tested sequence that shows the formation of each isotope, from which other isotope it comes from, how long it takes to decay, and which isotopes are created when it decays. That way we have a very precise way to calculate what will be the proportion of isotopes in a sample a given time after it was created.

All these experiments with isotopes can be performed with high accuracy in laboratories today. We have excellent motives, both theoretical and practical, to believe that the probability of radioactive decay is a precise and unchanging figure. That's why radioactive dating is such a reliable and precise method for dating objects.