The Second Book of General Ignorance (4 page)

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 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.

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 are 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.

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 pilchardu
s) 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.