by Calilasseia wrote:Ok, I'll strip out the nested quotes in this post to make life simpler.Agrippina wrote:Am I therefore right in saying that we should leave the white film that forms on aluminium alone? Or should it be cleaned off, people around here are obsessive about shiny window frames?
Indeed. Leave that film alone
Thank you. My husband says he can use that the next time some nosy-parker tells me about cleaning window frames.
Agrippina wrote:Good, that makes it clearer. But then also there weren't any fish in the water before there was oxygen in the atmosphere?:dunno:
Indeed, fishes did not start to appear, in their earliest forms, until around the Cambrian era. Oxygen had been a feature of the Earth's atmosphere for over a billion years before the first fishes arrived on the scene. One of the additional pieces of evidence for this, by the way, apart from the presence of geological formations requiring an Oxygen-free atmosphere in the early history of the Earth, followed by their absence once oxygenic photosynthesis got under way seriously courtesy of the cyanobacteria, is the presence of fossils of various green algae dating back to around 1.2 billion years before present, which added their own contribution to the Oxygen content of the atmosphere. A particularly famous one, for which I have the scientific paper, is Bangiomorpha pubescens - because this was the earliest known sexually reproducing multicellular eukaryote from the fossil record when it was found (it was alive a full 700 million years before the so-called "Cambrian Explosion", incidentally!), the author of the paper labelled it Bangiomorpha partly as a pun on the word "bang", used as a slang term for sex.
That's funny.
I originally thought that the earliest fishes dated from the Silurian era, because fossils of Agnathans (jawless fishes) have been known from Silurian strata for some time. However, it transpires that a Cambrian era fossil, Haikouichthys, has been found in strata dating back 518 million years, which places them in the late Cambrian. By the time we reach the Silurian, we also see the appearance of fishes known as Acanthodians, or spiny sharks, and complete fossils of Acanthodians are known from these strata, though some scientists are now claiming that incomplete remains (e.g., teeth) from these organisms have been found in earlier, Ordovician strata.
Whilst our picture of the history of fishes is incomplete, it is still extensive, as several million fish fossils have been found, belonging to thousands of Genera, ranging all the way from Haikouichthys in the Cambrian, to more recent Miocene fossils, for example. Once again, those fossils are arranged exquisitely in time and taxonomic order, in a manner that would be impossible to replicate by any fantasy "global flood".
And of course messing around with mixing fresh and salt water fish together.
I always enjoy watching documentaries about the pre-history of fishes. Fascinating. Which is why I enjoy going to Cape Town's aquarium.
Agrippina wrote:I understand that. Which is why simply distilling sea water is not quite enough to make it drinkable?
Actually, distillation of sea water is sufficient to produce potable (drinking) water. Basically, distillation in its simplest form involves heating the water until it boils, then condensing the steam elsewhere in the apparatus. The resulting water formed this way is free of dissolved salts.
However, because boiling water involves a LOT of heat energy, traditional distillation is hideously expensive. Which is why desalination plants take advantage of the Gas Laws to reduce the costs. I'll now explain how this works.
And of course why, in a water-hungry country like this one, it is simply too expensive to use the water source on our doorstep.
Every liquid has associated with it, a quantity known as 'vapour pressure', which is the effective pressure at which that liquid becomes gaseous at any given temperature. Vapour pressure increases with temperature, and when the vapour pressure equals the surrounding atmospheric pressure, the liquid boils and becomes a gas. Now, you'll be familiar with the concept of 'boiling point', which is the temperature you have to heat a liquid to in order to boil it, but this temperature changes with the ambient atmospheric pressure. So, for example, at sea level, where the atmospheric pressure is around 14.7 pounds per square inch (101 kilopascals in SI units), water boils at 100°C. However, if you take a container of water 10,000 feet up a mountain, you'll find that it boils at a lower temperature, typically around 85°C, which is why you can't make tea on a mountain top unless you use a pressure cooker - tea only forms if the tea leaves are infused at close to 100°C.
This is interesting. It explains why I always get very weak tea from our hot water dispenser.
However, this trick can be used to reduce the temperature at which you heat your water in order to convert it into water vapour. Basically, you perform your distillation under low pressure, so that you only have to heat your water to, say, 50°C instead of 100°C. There's a trade-off between the costs of maintaining a vacuum in a large apparatus, and using energy to heat the water, so there's an economic limit extant in desalination plants using vacuum distillation. But, if you take this process to its logical conclusion, it's possible to turn water into a gas at room temperature - you simply lower the atmospheric pressure in the container to that found at, say, 25 kilometres above the Earth's surface, at which point water will become a gas at room temperature.
Something else I didn't know.
Conversely, increasing the pressure allows you to heat water beyond 100°C, whilst still keeping it liquid, and this principle is used in pressure cookers, to cook food without leaching nutrients from the food. You can heat your food to 100°C, cook it thoroughly (and ensure that any bacteria are well and truly killed in the process), whilst still keeping the water liquid, and allowing your food to retain its nutrients. Pressure cookers tend to be more industrial than home devices, though, because they need to be made to proper engineering tolerances in order to maintain their structural integrity under the thermal and pressure stresses they are subject to, and if you find one of the home pressure cooking pans that were popular in the 1950s for a short while, you'll find that it's a heavy piece of kit, and not the sort of thing your average 1950s housewife could reasonably be expected to heft around the kitchen - it's a solid hunk of metal of the sort shot putters might throw around on the athletics field!
Ha! I remember those. I have one from the late 1970s; even that one is a "lump of metal."
Incidentally, whilst dwelling on desalination of sea water, an alternative method involving pressure exists, known as reverse osmosis. This works courtesy of the fact that certain membranes will allow water molecules to pass through them, but will stop molecules of various dissolves substances from doing so. The movement of water that takes place across such a membrane is known as osmosis. Normally, this is demonstrated in a school laboratory, by arranging for a tube constructed from one of these membranes, to be suspended in a container of fresh water, then filling the tube with salt water. What happens is that water molecules migrate from the fresh water in the container, through the membrane, to the salt water in the tube, and the volume of water in the tube increases, so that it rises within the tube. It's quite impressive when you see it for the first time!
Basically, water will always move, where possible, from regions of low concentrations of dissolved salts, to regions of high concentrations, and this is a central governing principle determining the physiology of fishes. Freshwater fishes have dissolved salts in their blood and body tissues that are at a higher concentration than the surrounding water, and so, they are constantly absorbing water from the surroundings. These fishes have therefore evolved osmoregulatory machinery to deal with this, usually by means of producing large quantities of very dilute urine via the kidneys. Saltwater fishes, on the other hand, have concentrations of dissolved salts in their body tissues that are lower than the surrounding sea water, and are consequently losing water through their bodies. To deal with this, they have evolved a different set of biochemical machinery. Saltwater fishes drink the surrounding sea water, and courtesy of special salt-secreting cells in the gills, expel the excess salt back into the sea. They also produce much smaller quantities of urine, and their urine is much more highly concentrated than that of freshwater fishes.
I remember learning about osmosis in my nursing education.
I didn't know about fish urine!
Having dealt with that little tangential diversion, back to reverse osmosis. Under normal pressure, water will migrate from low concentration regions to high concentration regions, and if there is a semi-permeable membrane permitting water movement, but preventing salt movement, water will move from the freshwater side of the divide to the saltwater side of the divide. There is a pressure associated with this movement, called osmotic pressure, which can be measured by suitable apparatus. But, because a pressure is associated with osmosis, it's possible to throw this into reverse. What you do, is you fill your tube with salt water, bring the ambient pressure of the salt water in the tube significantly above atmospheric pressure, and hey presto, fresh water appears on the other side of the membrane. This is used commercially not only in desalination plants, but in fishkeeping (something I've had my hands in now for 35 years!).
I only succeed in killing them.
Reverse osmosis systems are used in the world of fishkeeping, to produce the purest possible water for an aquarium, when keeping sensitive species in captivity, and are also used in the world of reef aquarium keeping to ensure that various substances found in tap water aren't transferred to the aquarium during a water change. Dissolved nitrate salts, for example, are bad for a reef aquarium, at least when they turn up in quantity, and if your tap water already contains 50 ppm of dissolved Nitrates, it's going to make the task of keeping certain sensitive species, such as large marine Angelfishes and many corals, that much more difficult. So, to remove these unwanted substances, you can now buy a reverse osmosis machine, that will strip these pollutants from your tap water, so that you can produce pure, Nitrate-free water for your reef aquarium, and keep your corals and marine Angelfishes happy.
I'll take your word for it. I can't keep fishes, I'm far too heavy-handed for them.
I like it when people alight upon ideas like this, simply by using their brain cells. Go to the top of the class.
Woohoo!
Agrippina wrote:And on the creationists, I think it's more fear of having to learn complex ideas and being afraid of admitting that they don't know something that causes them to not want to believe, rather than not able to believe.
The problem you have with creationists, is that these people have decided that they're going to prefer the unsupported assertions of a doctrine to reality, because those unsupported assertions require less work to understand. Make-believe is always easy for humans to handle, after all, it's an essential aspect of childhood play from about the age of 2½ onwards. And, because we are a storytelling species, we love making things up. If we didn't, there wouldn't exist the vast market for fiction that you see manifest in every bookshop. We as a species love making stories up, and love spreading those stories to other people. Combine this with our innate curiosity about our surroundings, and you have in place all the ingredients required to drive the development of mythology.
Mythology was, in effect, our first, blindly stumbling attempt to provide something resembling an 'explanation' for our surroundings. Our prehistoric ancestors, having worked out how to use fire, how to make tools, etc., were beings of intent, and consequently, regarded actions that took place before their eyes as the product of intent. In a sense, they could claim a very limited empirical basis for this, because they engaged in actions driven by intent, and thus provided evidence for the presence of intent behind action. They also regarded the actions of other organisms in the same light: for example, big predators that turned up were viewed as possessing an intent to feed, which, given the prehistoric humans' own intent in this regard, was a perfectly natural view for them to form. So, when they saw something such as lightning striking a tree, in order to try and place this event in a comprehensible framework, they looked around for something to compare it with by analogy, and lo and behold, they had one, courtesy of their recently acquired mastery of fire. Consequently, they developed the notion that the lightning striking the tree must be similar in some way to their striking sparks from their flints, and as a corollary of this, that there must be something aournd, resembling themselves, striking some very big flints indeed in order to set whole trees on fire. But, because they couldn't actually see whatever was doing this, they came up with the idea of a big, invisible version of themselves, that somehow managed to live in the sky. Once they had that idea in place, it was simply a matter of time before they started to make up stories about whatever this big, invisible version of themselves was, what it was up to, etc., etc. All that happened from then on, was that the stories being told were more and more embellished with the refinements of their developing cultures and civilisations.
Unfortunately, this approach, whilst it was eminently good enough for Palaeolithic man, has ceased to be in any way relevant to the real world for at least 300 years. One of the hilarious ironies of this development, of course, is that having alighted upon a proper version of the scientific method, some humans set out to use this in a charmingly naive attempt to validate their favourite mythology, only to have the real world turn round and say to them "sorry, but that particular collection of assertions is wrong". Those who recognised the utility value of the scientific method, and accepted that it worked, started abandoning the assertions of mythology, albeit in slow stages, when that method and real world observation taught them the lesson that particular mythological assertions were basically make-believe. But that storytelling tendency, our tendency to view everything in terms of intent as a consequence of our evolutionary heritage, remains a powerful influence, and when this is combined with the fact that certain mythologies have inspired ruthless enforcement of conformity to doctrine, some people have trouble letting go.
Nowhere is this more fatuously obvious than in the case of creationists. The universe and its contents have been revealed by science, and the diligent efforts of thousands of honest, hard working scientists, to be far grander, far more exotic and filled with wonder, than the narrow, parochial views expressed in 3,000 year old mythology. Indeed, scientists have alighted upon entities and phenomena that the Bronze Age authors of mythology were incapable of even fantasising about. Neutron stars, black holes, the workings of thermonuclear fusion in stars, the quixotic phenomena of the relativistic and quantum worlds, many of which have been directly observed in the laboratory, or deduced to exist from relevant astronomical observations, are so far beyond the ability of Bronze Age storytellers to contemplate, that the mythology they wrote is now hopelessly irrelevant with respect to the real world and what we know of its behaviour. Indeed, the very fact that scientists have alighted upon a vast array of entities and phenomena that were completely unknown to the authors of mythology, should be instructive and informative to anyone who pays attention.
Unfortunately, because it doesn't take much effort to accept uncritically the assertions of that mythology, whereas learning about the real world now requires considerable dilligence and application, courtesy of the sheer volume of what we have already learned, some people prefer the fantasies and make-believe of the past, and insist that all of the conscientious effort of those hard-working scientists must somehow be "wrong", and that the fairytales of the past must somehow be "right". The only basis for doing so in the modern world is lamentable, pathological indolence. It's the view of the lazy, the wilfully ignorant, the view of people who can't be bothered to get off their backsides and engage in real learning, and instead, prefer to shroud themselves in the comfort blanket of wishful thinking, because learning about how reality actually operates is too much hard work. More insidiously, that approach is manifestly morally corrupting, because, as is the case with all doctrines, the business of regarding the core assertions as constituting purported "axioms" about the world, enjoying a privileged epistemological and ontological status, protected from inquiry and critical examination, inexorably leads to the duplicity that is apologetics, the business of constructing ever more convoluted and fantastical fabrications, for the purpose of trying to force-fit reality to the doctrine, and in order to prosecute this activity, adherents of doctrine inevitably reach the point where they have to disseminate falsehoods in order to push the doctrine onto others. When reality says that your doctrine is wrong, you cannot help but disseminate lies when you try to tell people that your doctrine is right.
This explanation is excellent, it is worth repeating.
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