by John Lloyd
Titan’s chemical composition is thought to be very similar to that of Earth during the period when life first appeared here, and it is the only moon in the solar system with an atmosphere.
In 2004 Ladbrokes the bookmaker, in a joint publicity stunt with New Scientist magazine, offered odds of 10,000 to 1 against life being discovered on Titan. Would this be worth risking a titan on? (A ‘titan’ is the £100 million note used by the Bank of England for inter-bank accounting purposes.)
On balance, probably not. The development of DNA on Titan is unlikely because of the extreme cold and the lack of liquid water. However, some astrobiologists have suggested that Titan’s hydrocarbon lakes might sustain forms of life that would inhale hydrogen in place of oxygen. Another theory is that life could have reached Titan from Earth, through microbes clinging to rocks smashed out of Earth’s orbit by asteroid impacts. This theory is called panspermia (from pan ‘all’ and sperma ‘seed’ in Greek) and was used to explain the presence of life on Earth as long ago as the fifth century BC, when the Greek cosmologist Anaxagoras first proposed it.
What is certain is that, as the sun gets hotter, the temperature on Titan will also rise, making the conditions for life more likely. Whether, in six billion years or so, Ladbrokes will still exist to pay out any winnings is much less probable.
The Cassini–Huygens probe is named after the Italian astronomer Giovanni Domenico Cassini (1625–1712), who discovered four of Saturn’s smaller moons between 1671 and 1684, and the Dutch polymath Christiaan Huygens (1629–95), who discovered Titan in 1654. Among Huygens’s other achievements were working out the theory of centrifugal force, publishing a book on the use of probability in dice games, building the first pendulum clock and writing the first ever physics equation.
Where is the world’s saltiest water?
Not in the Dead Sea.
The saltiest water in the world is found in Don Juan Pond in the Dry Valleys of north-eastern Antarctica. Also known as Lake Don Juan, it’s really more of a puddle, with an average depth of less than 15 centimetres (6 inches). Its water is so salty that it doesn’t freeze, despite the surrounding air temperature of –50°C. The water is 40 per cent salt – eighteen times saltier than seawater and more than twice as salty as the Dead Sea (which is only eight times saltier than the oceans).
Don Juan Pond was discovered by accident in 1961 and named after two US Navy helicopter pilots, Lieutenants Donald Roe and John Hickey (hence Don John or ‘Don Juan’ in Spanish), who carried in the first field party to study it.
It’s probably the most interesting puddle on Earth. Given that Antarctica’s Dry Valleys are the driest, coldest places on the planet, it’s astonishing that there’s water there at all. It didn’t come from the sky – it’s too cold and windy there for rain or snow – it seeped up from the ground, slowly becoming saltier as the top layer of water evaporated. In spite of these unpromising conditions, the first researchers were amazed to discover it contained life: slender mats of blue-green algae that harboured a flourishing community of bacteria, yeast and fungi.
Since that first expedition, for reasons that are unclear, the water level in the pond has more than halved and no life remains. But even this is significant, because its waters still contain nitrous oxide (better known as laughing gas), a chemical previously believed to require organic life to produce it. This has now been shown to be a by-product of the reaction between the salts in the pond and the volcanic basalt rock that surrounds it.
If liquid water is found on Mars, it is likely to be in the form of cold, briny pools, just like Don Juan Pond. And we now know that at least some of the nitrogen-rich chemicals needed to produce life can occur in even the harshest environment.
Unlike Don Juan Pond, there is still plenty of life in the Dead Sea. There are no fish, but it is teeming with algae. This supports microbes that feed on it called Halobacteria. They belong to the Archaea domain, the oldest life forms on the planet. Archaea are so ancient that, on the evolutionary timescale, human beings are closer to bacteria than bacteria are to Archaea. Like the former inhabitants of Don Juan Pond, Halobacteria are ‘extremophiles’, surviving in conditions once believed impossible for life.
The Halobacterium is also known as the ‘Renaissance Bug’ because it can mend its own DNA (which is damaged by high salt concentrations). If this can be harnessed, it could be of great benefit to cancer sufferers. It might even enable manned space flight to Mars, by helping astronauts protect their DNA from exposure to the fierce radiation of interplanetary space.
Where did most minerals in the world come from?
Life on Earth.
There are about 4,300 minerals in the world today, but in the primordial dust that was to become the solar system there were fewer than a dozen. All the chemical elements were already there, but minerals were very rare before the sun and the planets formed.
Unlike all the other planets, Earth’s crust is a patchwork of constantly moving tectonic plates (‘tectonic’ is from the Greek for ‘construction’). No one knows why, but one theory is that all the water on the earth’s surface caused cracks in it, like damp from a flooded bathroom seeping through a plaster ceiling. As the plates of the young Earth jostled together, they created immense heat and pressure, pushing the number of minerals up to perhaps a thousand.
Then, 4 billion years ago, life appeared. Microscopic algae began using sunlight to convert the carbon dioxide that made up most of the atmosphere into carbohydrates for food. This released oxygen as a by-product. Oxygen is both the most abundant and the most reactive element in the planet’s crust. It forms compounds with almost anything. As it bonded with silicon, copper and iron, hundreds of new minerals were created. Although we think of oxygen as a gas, almost half the rocks on Earth are made from it.
While oxygen was being released into the atmosphere, carbon was also being sucked into the sea. Carbon, the basis of life, is as stable as oxygen is reactive. Its stability has made it the core of millions of organic compounds, including all the proteins, fats, acids and carbohydrates that go to make up living things. As the complexity of life on Earth increased, new minerals were created. Marine creatures died and drifted to the seabed, the thick layers of their shells and skeletons destined to become limestone, chalk and marble. Meanwhile, over millions of years, the sludge of rotting plants provided the ingredients for coal and oil. More life, and more diversity of life, meant more minerals. Two-thirds of all the minerals on earth were once alive.
This ‘parallel evolution’ of life and rocks gives clues to what we should look for on other planets. If certain minerals are detected, it’s a good bet that they came into being alongside particular types of organism.
Are we depleting the world’s mineral reserves? Oil aside, none of the evidence suggests so. Although vegetables grown in the UK and the USA over the past fifty years have shown significant drops in the levels of the trace minerals they contain, this is the result of artificial fertilisers, which promote faster growth at the expense of the plants’ ability to absorb nutrientsfrom the air and soil.
This may explain why people say that food ‘tasted better during the War’. They’re probably right.
Which came first, the chicken or the egg?
The egg. Final answer.
As the geneticist J. B. S. Haldane (1892–1964) remarked, ‘The most frequently asked question is: “Which came first, the chicken or the egg?” The fact that it is still asked proves either that many people have never been taught the theory of evolution or that they don’t believe it.’
With that in mind, the answer becomes obvious. Birds evolved from reptiles, so the first bird must have come out of an egg – laid by a reptile.
Like everything else, an egg is not as simple as it looks. For a start, the word ‘egg’ is used in two different ways. To a biologist, an egg is an ovum (Latin for egg), the tiny female reproductive cell which, when fertilised by a male sperm (Greek for seed), develops into an embryo. Both the ovum and the sperm a
re called gametes (from the Greek gamete, ‘wife’, and gametes, ‘husband’).
In a hen’s egg these two tiny cells merge in the ‘germinal spot’ or blastodisc (from blastos, Greek for ‘sprout’). Around this is the yolk, which provides most of the nutrition for the growing chick. The word ‘yolk’ comes from Old English, geolca, ‘yellow’ (until the late nineteenth century it was often spelt ‘yelk’). Around the yolk is the egg white or albumen (from the Latin albus, ‘white’) which is also nutritious but whose main purpose is to protect the yolk, which is held in place in the centre of the egg by two twisted threads called chalazae. (Chalaza is Greek for ‘hailstone’: the knotted white cord looks like a string of minute pearls or balls of ice.) Around the albumen is the shell, which is made from calcium carbonate – the same stuff that skeletons and indigestion pills are made from. It’s porous so that the chick can breathe, and the air is kept in a pocket between the albumen and the shell. Membranes separate each part and together it’s known as a cleidoic egg – from the Greek kleidoun, meaning ‘to lock up’. A chicken makes the whole thing from scratch in a single day.
Because its shell is porous, if you keep an egg for a long time, the yolk and albumen dry out, sucking air inside. That’s why rotten eggs float. To find out what colour egg a hen will lay, examine her earlobes. Hens with white earlobes lay white eggs; hens with red earlobes lay brown ones. The colour of a hen’s egg depends on the breed of the chicken: it has nothing to do with diet.
In 1826 the Estonian biologist Karl Ernst von Baer (1792–1876) proved that women produce eggs like other animals. Since the time of Aristotle, everyone had thought that a male seed was ‘planted’ in the woman and nurtured in the womb. (The first observation of semen under a microscope by Anton van Leeuwenhoek (1632–1723) in 1677 seemed to confirm this: he thought he had seen a miniature homunculus, or ‘little man’, in each sperm.) It wasn’t until the 1870s that the embryo was proven to develop from the union of egg and sperm and it took another twenty years before German biologist August Weismann (1834–1914) discovered that sperm and ovum carried only half the parent’s genes. The sperm is the smallest cell in the human body – it’s only a twentieth the size of an ovum – whereas the ovum is the largest. It’s a thousand times bigger than the average cell, but still only the size of a full stop on this page.
Can you name a fish?
Don’t even try: there’s no such thing.
After a lifetime’s study of the creatures formerly known as ‘fish’, the great palaeontologist Stephen Jay Gould (1941–2002) concluded they didn’t exist.
The point he was making is that the word ‘fish’ is applied indiscriminately to entirely separate classes of animal – cartilaginous ones (like sharks and rays); bony ones (including most ‘fish’, from piranhas and eels to seahorses and cod); and ones with skulls but no backbones or jaws (such as hagfish and lampreys). These three classes split off from one another far longer ago than the different orders, families and genuses did from each other, so that a salmon, for example, has more in common with (and is more closely related to) a human than a hagfish. To an evolutionary biologist, ‘fish’ is not a useful word unless it’s on a menu.
And this isn’t just a quirk particular to Gould. The Oxford Encyclopedia of Underwater Life comments: ‘Incredible as it may sound, there is no such thing as a “fish”. The concept is merely a convenient umbrella term to describe an aquatic vertebrate that is not a mammal, a turtle, or anything else.’ It’s equivalent to calling bats and flying lizards ‘birds’ just because they happen to fly. ‘The relationship between a lamprey and a shark’, the Encyclopedia insists, ‘is no closer than that between a salamander and a camel.’
Still, it’s better than it was. In the sixteenth century seals, whales, crocodiles and even hippos were called ‘fish’. And, today, cuttlefish, starfish, crayfish, jellyfish and shellfish (which, by any scientific definition, aren’t fish at all) still are.
Stephen Jay Gould made the same point about trees. The ‘tree’ form has evolved many times in the course of history: its ancestors were unrelated plants such as grasses, roses, mosses and clovers – so, for Gould, there’s no such thing as a tree either.
One fish that absolutely doesn’t exist is the ‘sardine’. It’s a generic term used for around twenty different small, soft-boned, oily fish. And only once they’re in a can. In the UK, they’re usually pilchards, often called – optimistically – ‘true sardines’, although the Latin name (Sardina pilchardus) points up the confusion. Sometimes what you get in a sardine can is a herring, sometimes it’s a sprat (which glories in the scientific name Sprattus sprattus sprattus).
What it isn’t, is a ‘sardine’. Nor even, as we now know, a fish.
ALAN At night all the ugly fish come out. And it’s really interesting.
STEPHEN You don’t need to be pretty out there.
ALAN That’s right. You go to the Red Sea and, in the day, the fish are beautiful, colourful fish. And then at night, they’re all bug-eyed. They limp around and you’re not allowed to touch them. And they all kind of look at you. And you shine a light at them and they go ‘No! No! Don’t look at me, don’t look at me!’
How does a shark know you’re there?
You don’t have to be bleeding for one to track you down.
Sharks have an astonishingly powerful sense of smell. They can detect blood at a concentration of one part in 25 million, the equivalent of a single drop of blood in a 9,000-litre (2,000-gallon) tank of water.
It’s the currents that determine the speed and direction of a smell’s dispersal in water, so sharks swim into the current. If you are bleeding, even slightly, a shark will know. If the current is running at a moderate 3½ kilometres per hour (about 2¼ miles per hour), a shark 400 metres (a quarter of a mile) downstream will smell your blood in seven minutes. Sharks swim at nearly 40 kilometres per hour (25 miles per hour), so one could reach you in sixty seconds. Faster currents make things worse – even allowing for the fact that the shark has more to swim against. In a riptide of 26 kilometres per hour (16 miles per hour), a shark less than half a kilometre (a quarter of a mile) downstream would detect you in a minute and take less than two to reach you – giving you three minutes in total to escape.
Sharks also see very well, but even a short-sighted shark with a bad head cold (not that it happens) would still be able to find you. Sharks have excellent hearing in the lower frequencies and can hear something thrashing about at a distance of half a kilometre (a third of a mile). So you could try being very quiet indeed.
A blind, stone-deaf shark with no nose would still find you without breaking stride. Sharks’ heads are riddled with jelly-filled canals by the name of the ‘ampullae of Lorenzini’ after Stefano Lorenzini, the Italian doctor who first described them in 1678. We’ve only recently discovered what their purpose is: to register the faint electrical fields generated by all living bodies.
So, as long as you’re not bleeding, not moving and your brain and heart aren’t working, you should be fine.
And there’s some more good news – sort of. Californian oceanography professor Dr Jamie MacMahan has found that the standard view of a riptide is wrong – it doesn’t run out to sea but is circular, like a whirlpool. If you swim parallel to the shore, he says, there’s a 50 per cent chance you’ll be swept out into the ocean deeps. But, if you just tread water, there’s a 90 per cent chance of being returned to shore within three minutes – perhaps just in time to escape the shark.
If a shark does find you, try turning it upside down and tickling its tummy. It will enter a reflex state known as ‘tonic immobility’ and float motionless as if hypnotised. Killer whales exploit this by flipping sharks over on to their backs and holding them immobile in the water until they suffocate. You have about fifteen minutes before the shark gets wise to your ruse. Careful, though: not all species of shark react the same way. Tiger sharks, for example, respond best to a gentle massage around the eyes. According to shark expert Michael Rut
zen, it’s just like tickling trout: ‘All you have to do is defend your own personal space and stay calm.’
Having said all this, relax. Sharks almost never attack people. Figures from all twenty-two US coastal states, averaged over the last fifty years, show that you are seventy-six times more likely to be killed by a bolt of lightning than by a shark.
Does the Mediterranean have tides?
Yes it does, despite what every tour guide tells you.
Most of them are very small: just a few centimetres back and forth on average. This is because the Mediterranean is cut off from the Atlantic (and the huge effect of the pull of the moon on it) by the narrow Straits of Gibraltar.
Right next door to the entrance to the Med, sea levels can change by around 80 centimetres (3 feet) but in the Gulf of Gabes off the coast of eastern Tunisia, the tidal elevation can be as much as 2.5 metres (8 feet) twice a day.
This is because tides are caused not only by the gravitational effect of the moon but also by atmospheric pressure, depth, salinity, temperature and the shape of the coastline.
The relatively big tides in the Gulf of Gabes result from its shape. It is a wide, shallow basin, about 100 kilometres (60 miles) wide by 100 kilometres long. The gulf acts as a funnel, the tidal energy forcing water into a progressively smaller space, thereby increasing the rise in sea level – and, correspondingly, lowering it on the way out. The same thing happens on a much greater scale in the Bristol Channel, which has a tidal range of over 9 metres (30 feet).