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Kindle Notes & Highlights
by
Brian Cox
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August 6, 2020 - October 30, 2025
The UV flux at the top of the Earth’s atmosphere would have been similar to that experienced by Mercury today, a planet around 100 million km closer to the Sun.
A UNIQUE AND COLOURFUL WORLD
THE ORIGIN OF LIFE’S COLOURS
There is a dazzling array of pigment molecules in nature, from carotenes that colour a carrot orange, to polyene enolates, a class of red pigments unique to parrots. In some cases the animals and plants produce the pigments themselves, but in many cases they are absorbed into the organism through its diet. If flamingos didn’t ingest beta-carotene from blue-green algae in their diet, their trademark pink colour would quickly turn white.
Pigment molecules perform a large variety of functions in living things. Some, as in the case of melanin, evolved to absorb light for protection. It is not known whether the first pigments were used for protection, although many biologists think this was the case. Protection is a simple function, needing no additional complexity such as a nervous system to respond to light’s stimulus. There are also pigments that simply make organisms colourful, in order to attract a mate, warn off a predator, entice insects to nectar or invite animals to consume vivid-coloured fruit.
Flamingos are pink because they ingest beta-carotene from blue-green algae in their diet.
FROM THE SMALLEST BEGINNINGS…
It is estimated that there are around 1031 bacteria alive on Earth – a hundred million times the number of stars in the observable Universe.
The oldest known bacterial fossils are almost 3.5 billion years old.
A single drop of water contains, on average, a million bacteria; a gram of soil may be home to 40 million; in your body there are ten times as many bacteria as there are human cells.
By mass, they are comfortably the dominant organisms on our planet.
Bacteria are organisms known as prokaryotes, which means that they do not have a cell nucleus. They share this trait with another group of single-celled organisms known as archaea.
All animals, plants, fungi and algae – in fact, anything that we would regard as ‘complex’ – are eukaryotes.
The overwhelming majority of biologists today believe that eukaryotes emerged from prokaryotes around 2 billion years ago, and that this fundamental and revolutionary change happened only once.
EATING THE SUN
6CO2 + 6H2o → C6H12O6 + 6O2 Energy from the Sun
Photosynthesis uses carbon dioxide and water to produce sugars and oxygen in a process powered by the energy of the Sun.
The purpose of photosynthesis, if you are a plant, is twofold. One is clearly visible in the famous equation: it is to make sugars, which is done by forcing electrons onto carbon dioxide. The other, which is hidden in the detail, is to capture energy from the Sun and store it in a usable form. All life on Earth stores energy in the same way, as a molecule called adenosine triphosphate, or ATP. This suggests strongly that ATP is a very ancient ‘invention’, and the details of its production and function could provide clues as to life’s origin 4 billion years ago.
In order to make sugars and ATP, therefore, the plant needs sunlight, carbon dioxide and a supply of electrons. It doesn’t ‘care’ where those electrons come from. The plant may not care, but we certainly do, because plants get their electrons from water, splitting it apart in the process and releasing a waste gas (oxygen) into the atmosphere.
These are cyanobacteria – lowly bacteria that sit at the very bottom of the food chain. They’re the most numerous organisms on the planet. There are more of them on Earth than there are observable stars in the Universe, and these little creatures are what enabled you – and every other complex living thing that has ever lived on the planet, from dinosaurs to daffodils – to exist.
A BREATH OF FRESH AIR
There is evidence that an early form of photosynthesis may have emerged as far back as 3.5 billion years ago in single-celled organisms that produced enigmatic mounds known as stromatolites (see Chapter 3), although the precise date is still an area of active debate and research. Whatever the date, there is general agreement that a simple form of photosynthesis, using energy from the Sun to synthesise sugars from carbon dioxide, just as photosystem I does in plants today, is very ancient.
The pigment used today is chlorophyll, a member of a family of molecules known as porphyrins. Complex though they are, porphyrins have been found on asteroids, implying that they form naturally and are likely to have been around on Earth before the origin of life.
There are still bacteria alive today that have only photosystem I. They take their electrons from easy targets, such as hydrogen sulphide or iron, and don’t ther...
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Over time, it is thought that some bacteria adapted this early photosynthetic machinery to perform a different task – the production of ATP. There are similarities between the two photosystems that str...
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The Oxygen Evolving Complex is an odd structure: more mineral than biological. It consists of four manganese atoms and a single calcium atom, held together in a lattice of oxygen. Manganese is locked away in vast mineral deposits on the ocean floor today, but in the early history of our oceans it would have been available in seawater for organisms to use. Bacteria use manganese to protect them from UV light, in much the same way as we use melanin – manganese is easily ‘photo-oxidised’, absorbing the potentially harmful UV photon and releasing an electron in the process. This may have been one
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But how does one cell end up inside another? At some point in the history of life on Earth, a cyanobacterium cell must have been engulfed by another cell and, instead of being digested, it survived to perform a useful purpose. This process, called endosymbiosis, has happened more than once in the history of life on Earth; indeed, it is thought to have been fundamental in the evolution of complex life. Endosymbiosis allows for great leaps in the capability of living things – a merger of fully formed skills to produce a result greater than the sum of the parts. In the case of oxygenic
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Chloroplasts convert light and carbon dioxide into carbohydrates.
The quite dizzying conclusion is that, because everything that carries out oxygenic photosynthesis today does so in precisely the same way, we owe the beauty of life on Earth – with its hues, colours and seemingly limitless diversity – to a cyanobacterium whose ancestors, somehow, found their way inside another cell. The descendants of that cell are still present on Earth today, inside every leaf, every blade of grass and every algal bloom, and they have filled our atmosphere with oxygen.
BREATH OF LIFE
Releasing energy from food using oxygen is around 40 per cent efficient, while oxidising food using iron or sulphur is only around 10 per cent efficient.
It is almost certainly no accident that the Cambrian explosion – the rapid diversification of life resulting in the emergence of virtually everything we would regard today as complex – followed (on geological timescales) a rapid increase in atmospheric oxygen levels.
BRINGING IT ALL BACK HOME
Why did life emerge so soon after the birth of our planet, only half a billion years after its formation? And how did the first life blossom into the magnificent complexity we see on Earth today?
FOUR-LEGGED LIFE STORY
There is something on which everybody agrees, however: as first proposed by the late Lynn Margulis, the eukaryote is a chimera, formed by endosymbiosis in much the same way as the ancestors of plants and algae acquired their chloroplasts.
Furthermore, eukaryotes bear an interesting genetic relationship with the two prokaryotic branches of life – bacteria and archaea. They share genes with both, which strongly suggests that the first eukaryote was the result of a merger between a bacterium and an archaea. The details are still the subject of debate, but it seems that something very unlikely indeed – the successful merger of two prokaryotic cells – had to happen before complex life could develop on our planet. The eukaryote is probably a happy accident. And, therefore, so are we.
To build Apollo 8, you first need a eukaryote, and it seems probable that on Earth this key step occurred due to blind luck, followed by a lot of natural selection.
It took almost 2 billion years for it to happen on our planet – 2 billion years in which the oceans remained a stable, hospitable home under a dangerous Sun.
Could it be that living things capable of taking pictures of their home from space are rare or even unique to Earth? Perhaps one day we will know, but, lonely or not, we have surely learnt enough about life’s...
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THE BRIEFEST OF BEAUTY
DAY OF THE DEAD
WHAT IS LIFE?
‘How can the events in space and time,’ asked Schrödinger, ‘which take place within the spatial boundary of a living organism, be accounted for by physics and chemistry?’
ENERGY AND THE FIRST LAW OF THERMODYNAMICS
The concept of energy is absolutely central to the description of any physical process, because it is always conserved. Because it can be neither created nor destroyed, all that can happen to it at the most fundamental level is that it is transformed from one form to another. In a sense, this is all there is to the Universe! If no energy is ‘flowing’ – a colloquialism by which we mean ‘being transformed from one form to another’ – then nothing is happening at all. Here is the first step on the road to answering Schrödinger’s question – What is Life? Whatever it is, it is a process by which
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FIRST LIFE
LIFE’S FIRST ENERGY SOURCE
ON PROFESSOR COX’S BATTERY AND THE ORIGIN OF LIFE
