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Swift
2014-Jun-27, 08:21 PM
From Laboratory Equipment magazine (http://www.laboratoryequipment.com/news/2014/06/fluke-may-have-made-life-land-possible?et_cid=4019635&et_rid=54636800&type=headline)


Terrestrial animals may owe a special debt to the sun and the moon. It may have been their combined pull on ancient Earth's oceans that helped primitive air-breathing fish gain a toehold on land, new research suggests.

In a new study, published in the journal Proceedings of the Royal Society A, physicist Steven Balbus argues that the gravitational forces generated by the sun and moon would have been conducive to the formation of a vast network of isolated tidal pools during the Devonian Period, between 420 to 360 million years ago, when fish-like vertebrates first clambered out of the sea.

“By the end of the Devonian, there were vertebrates that were quite at home moving around on land,” said Balbus, who is at the Univ. of Oxford.

According to Balbus, a rather remarkable confluence of cosmic, geological and biological events occurred during the Devonian period that helped jump-start life on land.


Link to the journal (http://rspa.royalsocietypublishing.org/content/470/2168/20140263.abstract?sid=9ecb37bf-d334-4b0b-b887-0a65424307b0)

Abstract:

The nearly equal lunar and solar angular sizes as subtended at the Earth is generally regarded as a coincidence. This is, however, an incidental consequence of the tidal forces from these bodies being comparable. Comparable magnitudes implies strong temporal modulation, as the forcing frequencies are nearly but not precisely equal. We suggest that on the basis of palaeogeographic reconstructions, in the Devonian period, when the first tetrapods appeared on land, a large tidal range would accompany these modulated tides. This would have been conducive to the formation of a network of isolated tidal pools, lending support to A. S. Romer's classic idea that the evaporation of shallow pools was an evolutionary impetus for the development of chiridian limbs in aquatic tetrapodomorphs. Romer saw this as the reason for the existence of limbs, but strong selection pressure for terrestrial navigation would have been present even if the limbs were aquatic in origin. Since even a modest difference in the Moon's angular size relative to the Sun's would lead to a qualitatively different tidal modulation, the fact that we live on a planet with a Sun and Moon of close apparent size is not entirely coincidental: it may have an anthropic basis.

profloater
2014-Jun-27, 08:27 PM
Sfunny, I thought that was a well established hypothesis, sbin on TV, sbin in the mags. SNice to know it's officially possible now! (The moon also stabilises our tilt long term and otherwise spin would topple, causing mass extinctions. so I heard)

cjameshuff
2014-Jun-27, 11:54 PM
The nearly equal lunar and solar angular sizes as subtended at the Earth is generally regarded as a coincidence. This is, however, an incidental consequence of the tidal forces from these bodies being comparable.

Given a constant density and constant angular size, tidal forces will be independent of distance, yes. The inverse cube falloff of tidal forces will be canceled by the cube increase in volume and mass of the body causing the tides. But...density isn't remotely constant. The moon's a lot denser than the sun, and could easily be a lot denser than it is. As for the forces being "comparable", the moon's tide is about twice as high as the sun's. If that's the criteria they're using for "comparable", then the angular sizes could vary widely from what they are...and we're back at it being a coincidence, even if their idea of having two "comparable" sources of tides being necessary is true. But even that seems like a weak argument...

Barabino
2014-Jun-28, 04:18 PM
if life on land depends on having sun and moon of roughly same apparent size, then another "Earth" must be extremely rare... :evil: "Mr Fermi" can go to restaurant just now, alone. No need to wait for other guests, there are none... :-(

Barabino
2014-Jun-28, 04:24 PM
BTW that rules out also tidally locked worlds... be them around gas giants or red dwarf stars... :-/

publiusr
2014-Jul-06, 08:01 PM
That's just as well. If life doesn't develop well there, that is an excuse for it to be deposited artificially.

Barabino
2014-Jul-21, 12:07 PM
As far as I understand this theory, tides have been instrumental not in developing life at cellular level, but in forcing some multicellular animals (marrooned off sea water) to adapt to land life... so it does not endorse or deny panspermia...

Noclevername
2014-Jul-21, 12:27 PM
As far as I understand it, tides have been instrumental not in developing life, but in forcing some vertebrates to adapt to land life...

That's pretty much what the OP says.

profloater
2014-Jul-21, 12:45 PM
As far as I understand it, tides have been instrumental not in developing life, but in forcing some vertebrates to adapt to land life...Well...without tides you do not get rockpools, Darwin might have been right.

cjameshuff
2014-Jul-21, 04:13 PM
That's pretty much what the OP says.

The OP is about an idea that's quite a bit stranger and which appears to have a number of major problems: that it was the combined tides from two objects of similar angular size, equating equal angular sizes with similar tides (ignoring the density differences and the fact that the sun and moon were not always of equal angular size, and ignoring the fact that the solar and lunar tides aren't all that similar), and equating two overlapping tides of similar amplitude somehow with development of life.

Noclevername
2014-Jul-21, 10:27 PM
The OP is about an idea that's quite a bit stranger and which appears to have a number of major problems: that it was the combined tides from two objects of similar angular size, equating equal angular sizes with similar tides (ignoring the density differences and the fact that the sun and moon were not always of equal angular size, and ignoring the fact that the solar and lunar tides aren't all that similar), and equating two overlapping tides of similar amplitude somehow with development of life.

With the advent on land of animal life.

lpetrich
2014-Aug-09, 03:33 PM
I think that tides are unnecessary. That's because land plants and land animals can colonize land from fresh water. In fact, it's easier for them to do so, because they would already be adapted to the sort of water that's available on most of the Earth's land surface: fresh water. Amphibians are all freshwater animals; I don't know of any saltwater ones. Likewise, land plants' closest aquatic relatives are green algae in division Charophyta, which are mostly freshwater ones.

Fresh water and seawater produce different survival challenges. Seawater is easy, because many organisms can produce the same solute concentration as the surrounding water, thus equalizing osmotic pressure. That means that water won't flow in or out. But fresh water has the problem of higher osmotic pressure, because there's much less dissolved in it. Organisms have to continually bail out water to survive, or else have cell walls strong enough to resist a balancing overpressure, otherwise they will drown. In fact, going back to the sea can cause problems. Both plants and animals can have problems with too much salt.

Lampreys and jawed vertebrates have a blood-chemistry curiosity: about 1/3 the solute content of seawater. That's rather unusual for marine animals, which usually have the same amount, but it's a plausible consequence of living in freshwater. Less solute means less water trying to get in. But that causes problems for going back to the ocean. One either excretes very salty urine, as ray-finned fish do, or else one adds something else to balance out the solute content, as sharks do. For ray-finned fish, I've found Nearly all marine fish came from freshwater ancestors « Why Evolution Is True (http://whyevolutionistrue.wordpress.com/2012/02/16/nearly-all-marine-fish-came-from-freshwater-ancestors/).

grapes
2014-Aug-09, 05:56 PM
The OP is about an idea that's quite a bit stranger and which appears to have a number of major problems: that it was the combined tides from two objects of similar angular size, equating equal angular sizes with similar tides (ignoring the density differences and the fact that the sun and moon were not always of equal angular size, and ignoring the fact that the solar and lunar tides aren't all that similar), and equating two overlapping tides of similar amplitude somehow with development of life.
I agree (with Noclevername's amendment, these are not Darwin's "little warm pools" for starting life), and I agree with your previous post. Just looking at the abstract, it's hard to believe that this was published in the Proceedings.

I can't seem to pin down the dates of what is referred to as Romer's work, in the article.

publiusr
2014-Aug-09, 06:02 PM
I think the idea of little pools where something just kind of happened sounded to some like substituting one miracle for another. That hurt folks accepting evolution.

With what we know now about tides mixing chemicals up, smokers acting like cracking stations, extremophiles--we see the violent, early Earth as a giant organic chemistry lab--with a lot of activity.

Now once life gets going and it gets deposited in a little pool, where the dynamic forces won't tear it right back apart again, then life can percolate a little in peace, as it were.

Life has always needed physical activity, followed by rest.

Barabino
2014-Aug-09, 07:06 PM
I think that tides are unnecessary. That's because land plants and land animals can colonize land from fresh water.

I was not there on those days (I'm not that old) but maybe seawater was not as salty as now when our tetrapod ancestors crawled out of the rockpools/out of of the ponds/whatever...

http://www.abroadintheyard.com/wp-content/uploads/Lobe-Finned-Fish-.jpg

grapes
2014-Aug-09, 07:57 PM
The issue in the article of the OP was not whether life evolved in tidal pools, but that the strong similarity of the visual size of sun and moon is necessary for life developing in those pools. Surely nonsense. But all I've read is the abstract.