As the plants died, the herbivores would follow quickly. Deprived of their food source, they would starve. The wild herbivores first. Elephants, rhinos, hippos, buffalo, wildebeest, zebra, giraffe, antelope, gazelle, deer… All would perish. Domestic herbivores would survive longer, sustained by stockpiles of hay and grain, but as these ran out, they too would die. Cattle, horses, sheep, pigs, chickens, turkeys. All would die.
Plants could still be grown indoors using artificial heat and light. Grown in giant greenhouses with fluorescent lighting. But only for a while. Only while the energy supplies lasted.
With the herbivores gone, the carnivores wouldn’t last long. Deprived of their prey, predators such as lions, tigers, leopards, jaguars and cheetahs would starve. And, although we might survive a little longer, humans would perish too.
The last remaining life on Earth would be microbial. The tiny microscopic microbes invisible to the naked eye. The bacteria and viruses. In time, however, they too would die, leaving the Earth a cold, dark, lifeless void.
22
Alien Life
The lull in proceedings as the world’s leaders debated what to do presented Liz and her colleagues with a rare moment of quiet. A chance to relax and unwind from the stresses and strains of the past months. To sit and chat over a cup of coffee, just like they did in the old days, putting the world to rights. As she leaned back in the sumptuous leather armchair in the ‘snug corner’ of the canteen, Liz studied the man sat opposite, the man she liked so much, the man who’d recruited her at Jodrell Bank. The kind, caring, compassionate, thoughtful, intelligent man who reminded her so much of her late father.
‘Liz,’ said Viv, placing his mug of hot tea on the table between them, ‘what do you think the aliens look like? Do you think they’ll look humanoid, like the extraterrestrials depicted in the movies? You know, like the greys with their large heads and big eyes, or bipedal reptilians like the Romulans in Star Trek. Or even like ET (Extra Terrestrial) himself. Or will they be more like the monsters in the Alien and Predator films?’
Liz sipped her coffee and smiled before answering. Her colleagues knew she’d written a dissertation on alien life as part of her PhD. ‘That’s how most people visualise aliens,’ she said, ‘but that’s got more to do with the power and influence of the movie makers rather than science. However, it might not be too far from the truth.’
‘You mean they might look like that?’ gasped Viv. ‘Like humanoids I mean.’
‘They might,’ said Liz. ‘Extraterrestrial life has always fascinated me. Intrigued me. That’s why I did my doctorate in astrobiology. It’s something I’ve thought about a lot. And read about too.
‘A good starting point,’ continued Liz, ‘as to what extraterrestrials might look like, is to study the evolution of life on Earth.’
‘Why’s that?’ said Viv, leaning forward in his chair. ‘Tell me more.’
‘Well,’ continued Liz, ‘one of the nice things about biology, and evolution for that matter, is that from really rather different starting points, in the tree of life, again and again, the same sort of solution arises. We call these universal characteristics, properties that are similar in species which are not closely related. For example, things like limbs – arms, legs and tentacles – eyes, flight and photosynthesis.
‘There are parochial characteristics too, properties unique to one species, like an elephant’s trunk or a panda’s thumb, properties not found in any other species. But let’s focus on the universal characteristics.
‘Universal characteristics are so useful they’ve evolved many times in many forms. Eyes are a prime example. The ability to sense light is probably the most useful feature of any organism, so it’s hardly surprising that eyes are common in many Earth species, often in radically different forms. Did you know that 96 per cent of animal species have eyes?’
‘No, I didn’t,’ said Viv.
‘Well, they do. The simplest eyes, like those of primitive worms, consist of just a few photoreceptors, nothing like enough to form an image but sufficient for the worm to distinguish light from dark. Then there’s the compound eyes of insects, the parietal eyes of reptiles and the most advanced eyes of all, the camera eyes of mammals, including ourselves.’
Continuing, she said, ‘At the molecular level, every eye in the world works the same way. Every one has a molecule that detects light – rhodopsin. As soon as light hits the rhodopsin molecule, it changes shape, causing its colour to change from pink to yellow. This change in structure triggers an electrical signal which ultimately goes all the way to the brain, where the signal is transformed into an image. It’s this chemical reaction that’s responsible for all vision on the planet. Molecules closely related to rhodopsin lie at the heart of every animal eye, which tells us that it must be a very ancient mechanism. Although we’ve been separated in evolutionary terms for over one billion years from a green algae called Volvox, we share one surprising similarity – the Volvox have light sensitive cells that control their movement and the active ingredient is a form of rhodopsin so similar to ours that we must share a common ancestor. That common ancestor is thought to be cyanobacteria, one of the first forms of life on Earth.’
‘I’m amazed that the first photosensitive cells appeared so early, and even more amazed that they were used for movement rather than sight,’ said Viv, enthralled by Liz’s detailed knowledge.
‘It’s surprising, I know,’ replied Liz, ‘but eyes are complex structures that took tens of millions of years to evolve.
‘Without eyes,’ she continued, ‘most organisms would die quickly. For instance, how long would a blind human last in the wild? Unable to see his surroundings, to find food or water, to sense danger, to see and evade predators, he would quickly perish. So would other blind animals. It’s sad, but nature is cruel. Cruel to be kind. It has to be to ensure that only the fittest survive.’
Liz paused to take a sip of coffee. Viv did likewise, taking a huge gulp of tea. ‘Please continue,’ he said, still leaning forward in his comfy leather chair. ‘I think I’m beginning to see where this is leading.’
‘The driving force behind universal characteristics is convergent evolution,’ said Liz. ‘Convergent evolution describes how similar traits are acquired by totally unrelated lineages. I’ve already mentioned eyes as a prime example of convergent evolution but wings are another good example. The wings of bats – a mammal – and birds – theropods, descendants of dinosaurs – are just extensions of limbs, of arms, having extended fingers or claws covered by membranes or feathers. The shape of wings is determined by physics: they have to be a certain shape in order to fly, so evolution converges on those shapes. If it didn’t, the wings wouldn’t function and the creatures wouldn’t fly. It’s the same for eyes – there are only so many ways to sense light. Convergent evolution always progresses towards an optimal solution to fit the prevailing environment. In a way, it’s a sort of determinism.’
‘But there’s another force at work too, isn’t there, Liz?’ said Viv. ‘Contingency.’
‘Yes, there is,’ said Liz, surprised by Viv’s knowledge of evolution. ‘Contingency, or radical diversity, is the impact of random, unpredictable events on evolution. Events that dramatically change the course of evolution. In a way, it’s the opposite of convergent evolution. But it isn’t a case of one or the other. Both convergent evolution and radical diversity operate together.
‘Perhaps the best example of radical diversity,’ continued Liz, ‘is the impact of the massive asteroid 65 million years ago which wiped out the dinosaurs, the dominant life form on the planet at that time.’ She paused, looked at Viv, and said, ‘Have you ever thought what would have happened if that asteroid hadn’t hit the Earth?’
‘It’s crossed my mind,’ said Viv, ‘but no, I can’t say I’ve thought deeply about it.’
‘If that asteroid had missed the Earth,’ said Liz, ‘then most likely we
wouldn’t be here. Dinosaurs would be the dominant life on Earth and mammals would still be small fur balls living between the cracks of an ecosystem dominated by dinosaurs. Most likely they’d have developed intelligence and the world would be run by intelligent dinosaurs. Dinoman would rule the Earth.’
‘It’s a sobering thought that such random, unpredictable events have such a profound effect on the course of evolution,’ said Viv. ‘It’s scary.’
‘It is,’ said Liz, ‘and we see the same thing in the Cambrian explosion.’
‘I know a bit about that,’ said Viv, pleased by his smattering of knowledge on evolution. ‘It’s the explosion of life that occurred around 600 million years ago, isn’t it?’
‘It is,’ said Liz, ‘and it heralded the first appearance of an animal with a backbone. The first chordate. There must have been many early chordates but only one survived, the pikaia chordate, the ancestor of all creatures with backbones, including the dinosaurs and ourselves. Why? Why did pikaia chordates survive and not the others? Why did these fail and pikaia and its ancestors become us? We don’t know. That’s what’s meant by radical diversity – there are no guarantees.’
Continuing, she said, ‘The genus homo has only been around for approximately two million years and the reason we’re in a mammal dominated world, not a dinosaur dominated world, is mainly because of the random, unpredictable event of an asteroid colliding with Earth. Determinism may dictate the shape and structure of eyes and limbs but that determinism can be changed in an instant by contingency, by radical diversity. Convergent evolution and radical diversity are in competition all the time and the direction evolution takes depends on which has the upper hand. The dinosaurs were optimally adapted for the conditions that existed 65 million years ago, but mammals, like us, are optimally adapted to the current conditions. It’s all a bit of a lottery really.’
‘So,’ said Viv thoughtfully, ‘if I’ve understood it correctly, convergent evolution produces universal characteristics, such as eyes, limbs and wings, that are extremely valuable to the organism, but such evolutionary pathways can be derailed, altered completely, by radical diversity.’
‘Spot on,’ said Liz. ‘You’ve grasped it well.’
‘And you think alien life will have developed along similar lines?’ said Viv.
‘The laws of physics, chemistry and biology are the same throughout the universe, so yes, I do. I expect to see similar trends in extraterrestrials. I expect them to have light sensing organs – eyes – skeletons to counteract gravity and stand upright instead of being a blob of matter, and I expect them to have limbs – arms, legs, tentacles and wings. In short, I expect them to have evolved physically optimal structures for sensing the environment, counteracting gravity and moving around. They’ll probably have parochial characteristics too, suited to their own particular environment. Despite the randomness of evolution, they have to obey the same physical laws, so we’ll probably recognise them quite easily when we see them. In fact, the humanoid and bipedal reptilian aliens depicted in the movies isn’t too crazy after all.’
‘What about intelligence? Is that a universal characteristic?’ asked Viv.
‘Intelligence is probably the most important characteristic of all to ensure the survival of an organism,’ said Liz. ‘Look at us, at homo sapiens. We currently dominate the planet because we’re the most intelligent species. But intelligence requires a large brain. Not only have large brains evolved independently in totally unrelated species, for example in apes, dolphins, octopuses, even crows, but in each case their cognitive world – what they sense and see – is surprisingly similar to ours, which supports the view that thinking, or intelligence, will be the same throughout the Universe.
‘What most people don’t realise,’ continued Liz, ‘is that large brains developed in tandem with sight in order to process all that data. As I mentioned earlier, an octopus has a sophisticated camera eye like ours and, like us, it also has a large brain. In fact, an octopus is the most intelligent non-vertebrate.’
‘I didn’t know that,’ said Viv.
Liz continued. ‘The last common ancestor between ourselves and an octopus existed 600 million years ago, suggesting a tantalising link between sensory processing and the evolution of intelligence.
‘But for one species, the desire to gather more and more sensory information has become overwhelming. That species is us. The increasing amount of data gathered by our senses drove the evolution of our brains and those increasingly sophisticated brains became curious and demanded more and more data. And so we built telescopes to extend our senses beyond the visible horizon and discovered a universe that was billions of years old and contained trillions of stars and galaxies. Our insatiable thirst for information has been the making of us.’
‘That’s fascinating,’ said Viv, obviously impressed by Liz’s knowledge and deductions, ‘but will alien life be based on carbon, like Earth life is, or are there other possibilities?’
‘Good question. Non carbon-based life is a favourite theme with science fiction writers,’ said Liz, ‘but carbon is unique. It’s the most important of the four light elements essential for life, the famous CHON quartet – carbon, hydrogen, oxygen and nitrogen. It’s the sixth element in the Periodic Table.1 Its electron configuration gives it remarkable properties. Carbon can form single, double and triple bonds, combine with itself in a myriad of ways to form complex chains and rings, and with other elements, especially hydrogen, oxygen and nitrogen, to form countless millions, even billions, of molecules. No other element in the Periodic Table comes close to matching these properties.
‘The molecules based on carbon, hydrogen and oxygen are the carbohydrates, the sugars and fats. Proteins and DNA use the same three elements plus nitrogen. Along with the two heavier elements, phosphorus and sulphur, these are the chemicals of life.’
‘But what about silicon-based life, isn’t that feasible?’ asked Viv.
‘Silicon is in the same Group as carbon in the Periodic Table,’ replied Liz, ‘so, like carbon, silicon also has four valence electrons in its outer shell, but its properties are quite different to those of carbon. Unlike carbon-carbon bonds, silicon-silicon bonds are weak, about half the strength of carbon-carbon bonds, so silicon can’t form long complex chains or rings. Also, its bonds with other elements, such as hydrogen and oxygen, are also weak, meaning it can’t form silicon analogues of carbohydrates, proteins or DNA. But there is one silicon compound which is very stable and very abundant. Silicon dioxide. Sand. Silicates are the most common minerals in the Earth’s crust, but they are inorganic, not organic, molecules and are useless for life. So no, silicon-based life is extremely unlikely.’
‘So we’re stuck with good, old-fashioned carbon-based life then,’ said Viv, draining the last dregs of tea from his mug.
‘I’d say so,’ replied Liz. ‘I can’t think of any other feasible alternatives.’
‘That’s been most enlightening, Liz. Thanks. But I’ve got one final question. Do you think the aliens will be peaceful?’
Liz hesitated before answering. ‘No, I don’t think they will,’ she replied, trying desperately to remember a quote she’d once heard, a quote that disturbed her. Suddenly, it flashed into her head. ‘Chances are,’ she said, ‘that when we meet intelligent life forms from outer space, they’re going to be descended from predators.’
‘What was that!’ exclaimed Viv. ‘What did you say?’
‘It’s a quote from Michio Kaku, an American physicist. And you know what, I think he’s right.’
As they were getting up to leave, Viv suddenly remembered where the alien meteorites had landed. ‘Liz, can life exist in extremely cold conditions?’
‘I’m glad you asked me that,’ replied Liz. ‘A large part of my thesis was on life at the edge, about organisms that can survive, even thrive, under extreme conditions. These so-called extremophiles can survive in really ha
rsh environments, including extremes of hot and cold, and…’
Liz’s answer was cut short by Rupert entering the canteen. ‘Frank wants us all to assemble in the meeting room. I think the world’s leaders have reached a decision.’
23
Plans
Manhattan in the dark should have been a beautiful sight. The most iconic skyline in the world ablaze with a kaleidoscope of coloured lights. Wall Street skyscrapers, the Empire State building, the equally impressive Chrysler building and the Rockefeller Center, all shining like beacons in the night. But not tonight. The buildings were still there, they hadn’t changed, but the lights had gone. Apart from a few dim specks emanating from the windows of inhabited apartment blocks, they stood in the gloom, forgotten relics silhouetted against a sombre, dark sky, like candles in the dark.
It was against this depressing backdrop that the world’s leaders, top scientists and military experts gathered together for one last face-to-face meeting. One last chance to meet in person before international travel became impossible. One last chance to try and resolve the deepening crisis engulfing the planet. Here, at the UN (United Nations) headquarters on the east side of Manhattan, New York. In future, any such meetings would have to be held using videoconferencing.
The meeting began with the General Assembly, giving all the nations of the world a chance to participate, to express their views. Their concerns. But it didn’t work. There were too many conflicting views, too many dissenting voices but, most of all, too much parochialism, with each country looking after its own interests. The main problem, however, was that 90 per cent of the countries represented had little to offer in the way of a solution. Few resources and even fewer, or no, technical capabilities. The world had done its duty by involving each nation but, after that first day, the remainder of the meaningful discussions were conducted by the UN Security Council, the small, powerful group of nations having the most advanced technology. Countries like the USA, Russia, Britain, France, Germany and China. These were the countries with the technological clout.
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