Extreme Organisms and Hydrothermal Vents

28 January 2007
Presented by Chris Smith, Helen Scales.

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This week we take a look at extreme environments and the organisms that live in them. Dr Crispin Little from the University of Leeds talks about hydrothermal vents and the fastest fossilisation on the planet, Professor Steve Scott from the University of Toronto explains why mining companies are interested in hydrothermal vents, and Dr Lisa Pratt from the University of Indiana describes how bacteria find energy three kilometres beneath the surface of the earth, and how similar strategies could be used by life on other planets. From the extremes of the Earth to the extremes of the kitchen, Derek Thorne and Hugh Hunt find out what's hot and what's not in the dishwasher...

In this episode

A Hop Skip and a Jump into a Time Capsule

Researchers in Australia are hopping with excitement having uncovered some of the most pristine fossils ever found in Australia, including 8 new species of kangaroo. The finds also tell a very different story of Australia in the past. Writing in this week's Nature, researcher Gavin Prideaux and his colleagues describe how they found a limestone cave in south-central Australia's treeless Nullarbor Plain. The entrance to the cave has periodically been opened and closed by natural events, and these have helped to keep the contents, which Prideaux describes as "the rosetta stone for scientists trying to understand past Australian climate", in excellent condition. "What must have happened is that animals fell into the cave, but they didn't die immediately. Instead they wandered away a short distance and so their remains are undisturbed." So far the team have dug through sediments at least three-quarters of a million years old and turned up the remains of birds, reptiles and 23 kangaroo species including 8 which have never been described before. But what is really exciting the team now are the clues that these remains provide to how Australia's climate must have changed in the last million years or so. The animals they've found are large herbivores; some of them would have weighed several hundred kilograms. But the Nullarbor plain is almost devoid of greenery and certainly couldn't have sustained such big plant-eaters, so the area must have been much richer in vegetation in the past. So did the climate change and turn a lush pasture into a treeless desert? No, says Prideaux, because stable oxygen and carbon isotopes in tooth enamel from the site can be used to calculate a record of past climate. These results show that the climate in this part of Australia, when these animals roamed, was almost identical to how it is today. So what's caused this transformation? "Wild fires," says Prideaux. And where did they come from. One word. Humans. "Most of these species were extinct by or soon after 40,000 years ago, at around the time when humans reached the south central coast."

How our Appetite for Eating Fish is Stripping Coral Reefs

This week, I published a paper based on research I did for my PhD, which looked at the growing trend for eating fish that have been collected from coral reefs all around the world and are flown to major Asian cities and cooked alive in luxury restaurants selling for extremely high prices. I found out for the first time just how devastating this trade can be, including for beautiful big fish like the Napoleon wrasse and large groupers - the sort of fish that scuba divers love to see when they visit coral reefs. By scrutinising the records kept by fish traders in Borneo, I discovered that within less than ten years the number of fish being caught by each fisherman had plummeted - a likely consequence of wild stocks being depleted. It is highly likely that these patterns of drastic overexploitation are being played out time and again in every country that hosts the trade in live reef fish. But, I hold out hope that it is not all doom and gloom and that we can improve the situation by increasing awareness among the consumers about where the fish they are eating came from, and by encouraging countries to cooperate and try to make sure the numbers of fish being traded do not exceed levels that the reefs can sustainably provide.

Smoking

Stroke Reveals the Smoking Gun behind Nicotine addiction

Scientists in the US have identified a coin-sized region of the brain responsible for nicotine addiction. Writing in this week's edition of Science, University of Iowa researcher Nasir Naqvi and his colleagues studied quit-rates amongst 69 smokers who had suffered strokes. 19 of the subjects had damage to a part of the brain called the insula cortex, and these individuals were much more likely to stop smoking in the wake of their strokes, often without difficulty, compared with subjects who had strokes affecting other parts of the brain. The effect was also more marked when it involved the insula in the right side of the brain compared with the left, but the study was too small to confirm the significance of this. So why this marked effect? Well, argue the researchers, the insula, which sits between the brain's temporal and frontal lobes, is thought to play a role in anticipating the bodily effects of emotional events. In other words it might help addicts to anticipate the pleasure of having a cigarette, and the relief from unpleasant withdrawal symptoms. In this respect it might help to motivate smokers to light up because it creates the feeling that smoking is a bodily need. But when this area of the brain is damaged it's as if, in the words of one patient, "the body has 'forgotten' the urge to smoke." The team hope that the identification of this link between the insula and smoking addiction will help scientists to better understand, with the help of brain scans and behavioural studies, the neurological basis of addiction, and develop better ways to help smokers to give up for good.

Dinosaurs may have Created the first Biplane

When the Wright Brothers flew the first ever aeroplane in 1903 it was seen as a masterful invention that would take humans into the skies, but in fact the idea of using biplane wings might have already been around for millions of years. Dinosaurs called microraptors lived in the Cretaceous Period around 125 million years ago and are thought to be some of the closest relatives of all the modern birds we see today. But unlike pelicans and pigeons these microraptors had two sets of wings, with large flight feathers stuck to their legs. Scientists used to think microraptors held their two sets of wings in a line, like a dragonfly, but a team of researchers from Texas Tech University in Lubbock think that would only have been possible if these flying creatures had dislocated their hips. Instead, a new idea is that microraptors held their wings one above the other, like a biplane - and this would probably have improved their gliding abilities, supporting the theory that bird flight began when dinosaurs jumped out of trees and glided, gracefully to the ground.

Dishwasher and crockery

Why plastic, but not china plates stay wet in the dishwasher

- Science Update - Squirrels, Trees and life on Mars

The Naked Scientists spoke to Chelsea Wald and Bob Hirshon, AAAS, the Science Society

Science Update - Squirrels, Trees and life on Mars
with Chelsea Wald and Bob Hirshon, AAAS, the Science Society

Bob - This week for the Naked Scientists, squirrels locked in a life and death struggle with spruce trees. But first, Chelsea has this report on a new theory of how life could exist in the extreme conditions of Mars.

Chelsea - Despite some curious data, most scientists believe the Viking missions of the 70s didn't find signs of life on Mars. But now astrobiologist Dirk Schulze-Makuch of Washington State University says the data may suggest life of a different kind. On Earth, life is based on water, which would freeze on Mars. But Schulze-Makuch points out that life based on a mix of water and hydrogen peroxide could survive.

Dirk - The hydrogen peroxide-water solution is actually quite neat in that way that it would allow near-surface life on Mars at current conditions. And not only that, it would explain nicely the Viking result.

Chelsea - If this sort of life does exist-and it's still a huge if - he suspects it would be tiny and single celled. He adds that the experiments Viking performed not only would have missed this life-they almost certainly would have killed it.

Bob - Thanks, Chelsea. Well, it's not as sensational a survival story as life on Mars or at the bottom of the ocean, but the red squirrel and the white spruce are locked in an epic battle over seeds. Scientists thought the tree had found a winning tactic: starve the squirrels of seeds for several years and then produce a bumper crop just when its enemies' numbers are low. But ecologist Stan Boutin of the University of Alberta says even that wasn't enough.

Stan - The squirrel has countered this strategy by actually anticipating when the trees are going to produce the big amounts of seed and producing another litter of babies. So the squirrels have produced a counterstrike against the trees.

Bob - And as in all great epics, the protagonist's downfall is of his own making. Boutin says the tree may inadvertently reveal its intentions to the squirrel through the hormones in its buds.

Chelsea - Thanks, Bob. Next time we'll join in the discussion about pain and suffering-we hope without causing you any. Until then, I'm Chelsea Wald.

Bob - And I'm Bob Hirshon, for AAAS, The Science Society. Back to you, Naked Scientists.

- Fossilisation at Hydrothermal Vents

Crispin Little has been studying the fastest fossilisation in the world at the bottom of the ocean

Fossilisation at Hydrothermal Vents
with Dr Crispin Little, University of Leeds

Chris - You're interested in hydrothermal vents, but some people may not know what they are, so could you just tell us a little bit about the geology of what these things are?

Crispin - Well it's a pretty simple system really. What you have is a huge underwater range of mountains on the sea floor where new ocean crust is being formed, and these are longer than any mountain chain on the surface. At these sites, because you have new ocean crust being formed, you have heat. Basically you have magma under the ground that rises via lava to form new ocean crust. And at the same time you have water, because you have ocean sitting on top of these huge underwater volcanic mountains. So what happens is that sea water seeps down and gets heated up by the magma chambers underneath the ground and as it gets heated up it reacts with new volcanic rock. It takes on all the different chemical compounds including hydrogen sulphide, which is very important, and lots of metals as well including iron, copper, lead and zinc. Because it's hot and buoyant, it rises back onto the sea floor and it jets out in certain places at these mid-ocean ridges to form big deposits of sulphide minerals in particular. The water that gushes out, which you said was near boiling, well if that water was gushing out at the land surface, it most certainly would be boiling because it's up to 400 degrees centigrade. It doesn't boil on the surface of the sea floor because it's under extreme pressure. In some places such as the cruise I was on recently, we were diving in to 2500 metres of water, and that's a lot of pressure on top of this vent fluid and it stops it boiling. So it's a pretty simple system in terms of its geological process of formation.

Chris - And so this is a massive source of energy; both chemical energy and thermal energy on the sea bed. So there are now organisms that can exploit that. I say now, but I mean that organisms have evolved over time to exploit that.

Crispin - Indeed and in fact there's evidence and some people suggest that life itself may have started at hydrothermal vents in the first place. These things are actually pressure cookers of organic compounds so it's a system that's been going on for billions of years in the world's oceans. Life may have started there and certainly it's an amazing site for all sorts of different life today.

Helen - What sort of life would we see down there? What sort of animals, plants and creatures? What lives down there?

Crispin - Well there are certainly no plants because remember it's completely black; as black as black can be. What you see are very specialised communities that can live at these hydrothermal vent sites and very challenging fluids, because not only is it very hot, but there's no oxygen in it and it can be quite acidic too. So pretty unpleasant stuff, but it does have a huge number of reduced chemical compounds in the fluid and if you can combine those fluids with oxygen for example, you can release a lot of energy, and that's the basis of these communities.

Chris - Are they just microbes, Crispin, or are we talking bigger animals?

Crispin - No there are bigger animals. The first thing that you'll see if you dive on the vent communities on the East Pacific Ocean for example, are these very big tube worms. These tube worms called Riftia, it's the giant tube worm and the most charismatic beast, is up to three metres long and not only can they grow three metres long but they can grow that big in a couple of years, so they're very very fast growing indeed.

Chris - But what are they eating?

Crispin - The intriguing thing about them is that as adults, they don't have a functioning gut at all. They don't have a mouth, they don't have a digestive tract and they don't have an anus. What they have is a body that's composed of what is essentially a bacteria farm, so they have billions and billions of little symbiotic bacteria. The bacteria are using hydrogen sulphide from the vent fluid for their energy source, and the tube worms bring hydrogen sulphide from the vent fluid and oxygen in its blood to the bacteria farms in the body. The bacteria then combine these two things, the oxygen and the hydrogen sulphide, to make energy. The animal then uses the bacteria, probably by eating them directly.

Chris - So where do the bacteria live in relation to the worm? Do they live on the surface or does the worm have special pouches to keep them in?

Crispin - It's actually an organ called the trophosome, and it's formed from skin cells. It's internal to the animal's body; not on the outside.

Chris - Reminds me a bit of the leaf cutter ants that farm fungi and they have special pores each fed by its own sweat gland, which nourishes a certain strain of bacteria that pump out a form of antibiotic. These ants can then distribute this around their nest to get rid of the fungi. So similarly you have worms that have structures that can accommodate these hydrogen sulphide-loving bacteria, and in return for accommodation, they can give something back to the worms.

Crispin - Exactly. And in fact it's not only the giant tube worms that can do this. There are two different sorts of bivalve shells, the giant vent mussel and the vent clam, which also do similar things. But here the bacteria are in the gill tissue. The gills are what bivalves usually do to filter feed, but in this case they're taken up entirely by these symbiotic bacteria in their tissues. So their gills are extremely large indeed for deep sea bivalves.

Chris - Why are they so big because there doesn't seem to be an obvious advantage to being so big because when you're a big animal in the sea and things find it harder to hunt you, it's an advantage. But for something like this where chemicals drive your existence, is there an advantage to being huge?

Crispin - Well I suppose so, firstly because you can have more symbiotic bacteria. The thing is that the energy available is almost indefinite. There's more energy than you can make use of, so the larger you are and the more bacteria you have in your bacteria farm, the better.

Chris - Some people have said that this is evidence that life could exist on other planets. Because if you can get a very specialised ecosystem like this on the bottom of the sea where the energy supply comes from the heat of the planet, this means that if you could find another planet somewhere in the solar system with a similar environment, you could have life there. But then others have come along and said that that's all very well, but there are still elements to that sort of ecosystem that rely on energy input from the sun, and if you took the sun away, they wouldn't survive.

Crispin - I think that if you look down at the bottom of the food chain here, to the bacteria and the archaea, this other kingdom of life you have amongst very small prokaryotic beasts, then I can't see why you couldn't have a similar system on other planets. Really for the starting process all you need is the heat source and some rock to react with the water, and you could have that on any rocky planet.

Chris - But where do you think these worms came from, because the bacteria that nourished them is one thing, but they're obviously very specialised organisms?

Crispin - If you have a look at their genes for example, they seem to fit quite nicely into polychaete worms, so things like the ragworm for example would be in this group. So while they are pretty specialised, they seem to have rather mundane origins. But we find fossils going back into the geological record that look very similar indeed. It's almost 430 million years, our oldest example. So similar sorts of beasts have been around for a very long period of time at vent sites.

Helen - Crispin, you're actually a palaeontologist, so I guess your interest is mainly what used to be there on the ocean ridges and in the process of fossilisation. I believe you've recently come back from a trip to the Pacific, and I was wondering what it was that you were doing during that trip to the ocean.

Crispin - The reason for going out on a cruise to modern hydrothermal vent sites is that I'm very interested in the process of fossilisation. So we find fossils of these things back in the geological record, but I don't really know how the process occurs - no-one does. The reason for going out on a modern cruise is to do some experiments on the sea floor and just see what this process is by looking at modern sites.

Chris - Were you exploring these vents remotely or were you in some kind of submersible that would take you down personally to see them?

Crispin - Unfortunately not me personally on this trip but yes, we were using the deep sea submersible Alvin, which is a very famous vehicle and was the one used to discover the Titanic, the Bismarck and hydrothermal vents were first discovered by Alvin in 1977. So we were taking Alvin down and it has three people on board: the pilot and a port and a starboard observer, who direct the science on the trip. So they were actually going down in the submersible and they were putting down experiments at the vent sites and bringing stuff up and collecting animals. They were diving each day on the research trip I was going on.

Helen - And what were the experiments you were doing?

Crispin - Well my experiments were a relatively simple system. I have a titanium mesh cage box with a base twelve centimetres across and six centimetres high. Inside that titanium mesh cage, I wire up different objects to see how they become mineralised. So I have tube worms, bits of shells from gastropods and bivalves, bits of shrimp carapace, and then some control materials as well. So each one of these titanium mesh cages is identical, and the idea is to put them onto hydrothermal vent sites as well as control sites, and just see how quickly this process occurs.

Helen - Because it's quite quick isn't it? That's the key that we're looking at fossilisation far quicker than anywhere else in the world really.

Crispin - Exactly. It's going to be nothing like our normal process of fossilisation that occurs in sediments, which we think might take hundreds or thousands or millions of years. This thing happens really quickly and we know that because if you look at some of the animal tubes of the worms that build their tubes on the outside of the mineral chimneys, the animals are still living in the tubes where part of the tubes is actually becoming fossilised. So it's a process which occurs during the life of the animal, which is really pretty extraordinary.

- Extreme Bacteria in the Earth's Crust

We look at bacteria found in the bottom of gold mines in South Africa

Extreme Bacteria in the Earth's Crust
with Dr Lisa Pratt, University of Indiana

Chris - Could you tell us a bit about the bacteria that you've been looking at?

Lisa - Well this is an organism that we sampled from water that was intersected in a very deep gold mine in South Africa. It requires a whole team of people to collect these samples and a lot of cooperation with the mine owners and the mine operators. Mining operations have a water intersection, often this water is under very high pressure and is very hot. They get in touch with scientists who are interested in studying that water and studying the possibility of organisms living there. We come in once the water flow has slowed down enough to be safe. We take the samples, we concentrate the organisms on filters and we ship those samples out to labs around the world and have a look at them. In this case, a water sample collected almost 2.8 kilometres below the surface yielded a very interesting community of organisms but with a single dominant bacteria that is making its living doing a sulphate reduction. Which in many ways is just the opposite of the chemical reaction that Crispin was talking about on the sea floor.

Chris - So how do you think these bacteria got there? Because it's not trivial for bacteria to be living 3 kilometres underground in water at high temperature and pressure.

Lisa - We assume they get there in much the same way as organisms in the present day move into the sub-surface. They gradually move downward with descending ground water, the circulation is very slow so by the time they get down several kilometres below the surface they've probably been in transit for tens of millions of years and have been isolated from their surface relatives for an extended period of time.

Chris - How long do you think these guys were isolated from the rest of the world?

Lisa - Well in this particular water sample, we've estimated its age by looking at the concentration of various noble gases and it appears to be something around 16-25 million years old.

Chris - So this water's been cut off from the outside world for 16-25 million years but it's still got loads of bacteria thriving in it?

Lisa - Yes

Chris - So what's powering them?

Lisa - Well that's a tough question because when we realised that these were sulphate reducing organisms we of course then went looking for a source of sulphate. Now that's a very common ion in seawater but there's no way we can imagine for sea water to get into this deep part of the basin. It could also come from dissolving ancient salt deposits but the rocks that these bacteria are in do not contain evaporitic salt-like minerals. So we started looking for another chemical pathway. And because these deposits are both rich in gold and rich in uranium, we came to the rather startling conclusion that most likely this was sulphate that resulted from radiolysis of water, which is the spitting of water molecules, and then the reaction between those fragments of water and the mineral pyrite, which is an iron sulphide mineral.

Chris - So what splits the water molecules in the first place, Lisa?

Lisa - Well of course we all hear a lot about the radioactive decay of uranium and when this process goes on it can be concentrated in the core of a nuclear reactor or dispersed as uranium-bearning minerals in the sub-surface. So here the uranium is present as a natural part of the sedimentary deposits and undergoing radioactive decay. It is releasing high energy particles and that ionising radiation is actually tearing through the water and breaking water molecules apart and creating hydrogen peroxide and hydrogen gas. And we think it's the hydrogen peroxide that then reacts with the pyrite.

Chris - Do you think that these organisms can teach us anything about: a) the possibility that life could have evolved independently on other planets which have a radioactive core or radioactive elements in their core, a bit like the earth does, and b) about ways to get energy out of things like this?

Lisa - Well I think the answer to both questions is yes. We have never before thought in terms of radiolysis of water as a source of energy to sustain organisms. So that's a very exciting discovery. And it suggests that even if you had a planetary body very distant from it's associated star, too distant to really rely on photosynthesis, you might have organisms that instead rely on this chemical energy caused by radioactive decay. In terms of what it tells us about earth, I think it reminds us that we know very little about the extreme environments on earth and we still have much to learn about our own planet.

Chris - How do you know that these bacteria that you've isolated were genuinely in the water that came out of this crack? How do you know that the water you've collected wasn't just contaminated from elsewhere in the mine when you broke open that sealed off bit of water?

Lisa - Always a tough question when we're working in these deep sub-surface environments, especially when we're working in mines. But in this case, the types of organisms that are present in the intersected water are distinct from the organisms that are present in the water that is utilised by the mine from surface sources. So it has a distinct phylogeny; its genes are different from its nearest surface relatives. And the amount of organisms that are there are consistent with their being sourced from these deep sequestered waters.

- Mining Hydrothermal Vents

Steve Scott looks at mining useful mineral from the bottom of the ocean.

Mining Hydrothermal Vents
with Professor Steve Scott, University of Toronto

Chris - Earlier in the show we heard from Crispin about how hydrothermal vents provide a home and a source of food to a range of species. But researchers are also now looking at these vents as a source of minerals and metals. So here's Steve Scott from the University of Toronto. He's a professor of ore genesis and is going to tell us all about it.

Steve - The deep sea occupies a big part of our planet. The oceans are 71% of our planet and the deep sea is about 80% of that, so there are a lot of secrets of the deep ocean that we're just beginning to understand. One of these is the hot springs that are deep on the ocean floor, spewing out fluids as high as 420 degrees centigrade. In these fluids are dissolved metals such as iron, but more interesting economically is copper, zinc, lead, silver and gold, that are precipitating around these hot springs on the sea floor and building up towering chimneys as much as 40 metres high. These are of course unstable and eventually fall over and produce accumulations of chimneys that grow into mounds and produce what to all intents and purposes are ore deposits on the ocean floor.

Chris - How abundant are those ores, Steve? How much of them is down there?

Steve - There are about 350 sites that we know about now and in total thousands of these so-called hydrothermal vents. Some of them are very small and would fit in somebody's dining room. Others are quite large, for example the ones in the Bismarck Sea off the coast of Papua New Guinea. Some of those deposits are a few hundred metres in diameter.

Chris - So are they actually exploitable, because some people have suggested that these particular ore deposits are much more enriched than ore we could get out of the ground normally in mine, and so are worth pillaging to get the goodness out.

Steve - Yes I definitely think they are exploitable, at least the ones in the Mannas Basin which is actually a site that I discovered back in the 90s. Our own sampling, plus much more detailed sampling by a mining exploration group called Nautilus Minerals, has verified that this is incredibly rich. They took a 15 tonne bolt sample out of one of the deposits and it averaged at something like 5.2% copper and 6.6 grams per tonne of gold. A typical mine of this type on land of volcanic rocks, which we have around the world in various places and lots of them in Canada, they would average about 2-4% copper and maybe a gram or two per tonne of gold.

Chris - Is it actually economically viable to recover though, because whilst it may be richer, you have the added problem of lots of sea water above you?

Steve - Yes you've got a lot of sea water. The Mannas Basin site, it's in 1600-1700 metres of water. But there are mines on land that are down 3000 metres, for example in Timmons, a Kid Creek mine here in Canada, and it's a whole lot easier to go down through a couple of thousand metres of water than a couple of thousand metres of rock. All you have to do is put a pipe down there, whereas on land you have to do an awful lot of blasting and drilling, which is very expensive to do.

Chris - Can you actually do an environmental calculation to work out which is better for the planet in the long run? Is it better to go down to these pristine marine environments and exploit those, or is it better to do the drilling and blasting that you mention?

Steve - I personally think that the ocean mining would be less of an environmental problem than mining on land. And it's a not a question of out of sight, out of mind, as no-one will accept that. On land you have to drill big holes in the ground. If you have an open cast mine, you have got to remove an awful lot of barren rock to get out the ore. Maybe for every tonne of ore, you might have to move five to ten tonnes of barren rock and you have to put that rock somewhere. You also leave a big hole in the ground and when it rains it produces acids from the breakdown of the iron sulphides to make sulphuric acid, and creates acid mine drainage, which is a big problem. In fact those are the three biggest problems of mining on land. In the oceans, you won't generate acid drainage because the oceans are alkaline, so you just don't generate the acids. They'll be no big holes in the sea beds because these things are sitting like big bumps on the sea floor, and you're going to remove that bump. It's referred to as surgical mining; you take just the ore and so you're not removing any waste rock. So the three biggest problems for mining on land just don't exist in the oceans.

- How do mousepads work?

How do laptop mousepads and iPod scroll wheels work?

How do mousepads work?

The pads are electrically sensitive to capacitance, or how much charge you can store in a certain area of the pad. When you put your finger on you need to have good electrical contact between your finger and the pad. Then it works out effectively how much charge is stored on that spot. It's got a matrix or array of wires running in one direction, and then the other direction. So it can literally use the x and y to work out where your finger must be. As you move your finger it's sensing how the stored charge moves across the pad. It resolves that into a direction and translates it into movement of the pointer on the screen.

- Why does water feel cold when air would feel warm?

Why does 27 degree air feel hot but water of the same temperature feels cold?

Why does water feel cold when air would feel warm?

That's to do with conduction. Water conducts heat much more readily than air so it's simply sucking heat out of your body, which makes you feel cold. If you think about wind chill, you can go out in the Antarctic and on a very still day which is minus 30 degrees you won't actually feel that cold. It's the movement of the wind past you that makes you cold. Those air molecules passing over you are each stealing a little bit of energy from the surface of your body and then moving on so you cool down much quicker. If you're wearing a wetsuit in water you have a single layer of water around you that warms up. Without a wetsuit the water is moving around you and robbing your body of energy all the time and cooling you down. This is why if you fall into cold water you should keep your clothes on and stay still and not swim around.

- What causes my manure heap to heat up?

What causes my manure heap to heat up and steam?

What causes my manure heap to heat up?

It's all about bacteria breaking down organic waste into compost, that stuff you can put on your roses to make them grow nicely. Basically breaking down organic compounds generates heat in the process. It's similar to when our bodies metabolise things, these chemical reactions that are going on create heat. Mainly in our liver, which is a huge source of energy production in the body. A manure heap is a thriving community of microbes all producing heat and similar things happen in farmers hay bales which can get so hot they cause fires!

- Why does stress cause palpitations?

Why does stress cause palpitations and then anxiety or chest tightness?

Why does stress cause palpitations?

When you're stressed, it initiates your body's fight or flight reaction, which is when you're preparing to do battle or run away from somebody. This pumps out loads of adrenaline, which causes your blood vessels and your heart to react. In order to get more blood to the rest of the body, the heart increases how hard it pumps and how fast it pumps, and what people are talking about when they say 'palpitation' is the feeling of your heart beating abnormally fast or hard. So it's all down to adrenaline, and it's also what causes panic attacks.

- Can I avoid altitude sickness?

Is there a way that I can train myself in advance to avoid the risk of altitude sickness? I'm going to Tibet early in the year and I don'...

Can I avoid altitude sickness?

When you go up a mountain, there's less oxygen, and because there's less oxygen your body recognises this and starts to breathe a lot harder, so your rate of breathing goes up. Whilst this does increase the amount of oxygen in the blood, it decreases the amount of carbon dioxide stored in the blood. Carbon dioxide is a weak acid, and what this does is make your blood more alkaline, which is what makes you feel unwell. So that's why hyperventilating makes you feel dizzy because you lose carbon dioxide. There's a drug called acetazolamide, which is a carbonic anhydride inhibitor. How that works is that it stops your body converting the stored acid back into carbon dioxide, so it keeps your blood a little bit more acidic and you feel better. People in the Andes swear by cocaine or coca tea.

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