If this theory is right, the basic machinery of life, up to and including DNA, was formed inside the rocky chambers of vent systems like those found at the Lost City, and you carry the evidence inside you to this day. Inside your cells, you are recreating the conditions that were present in the primordial oceans of Earth 4 billion years ago. You are making proton waterfalls, because that’s what life has always done. When the chemistry inside the vents became sufficiently complex to begin replicating, passing genes down the generations, natural selection could begin to weave its magic. Life found a way to manufacture its own proton gradients, using the out-of-equilibrium conditions beyond the vents, and it put a bag around the whole thing and left. And that is how you came to be.
The basic machinery of life, up to and including DNA, was likely formed inside the rocky chambers of vent systems like those found at the Lost City, and you carry the evidence inside you to this day.
Three of Saturn’s moons float over and underneath its rings in this Cassini Orbiter view.
Life beyond Earth
The theory for the origin of life on Earth that we’ve presented here is certainly plausible, and there are a number of well-respected biologists who support it. As we’ve emphasised throughout the book, however, an argument from authority is no argument at all. Is there any way the idea that life began in vents could be tested? One way would be to build an artificial vent in the laboratory, in much the same way as Urey and Miller constructed an artificial warm little pond. A group run by Nick Lane at University College London is doing just this, with the aim of observing how complex organic chemistry might emerge in out-of-equilibrium conditions such as those found in the Lost City vents.
There is another possibility, though. If it is true that the spontaneous emergence of life is near-inevitable, given the right conditions, and that vent systems were the cradle of life on Earth, we might expect life to be present on any world that has alkaline vent systems in mildly acidic oceans. It is terrifically exciting that we may well have discovered at least one such world on our own doorstep.
Enceladus above the ring plane. The ice fountains at the South Pole are just visible.
In February 2005, NASA’s Cassini spacecraft began to detect something strange about a small icy moon called Enceladus. The moon is only 310 miles across, and the Voyager spacecraft that passed through the Saturnian system in the early 1980s did not return detailed images of its surface. Cassini’s precision measurements of Saturn’s magnetic field showed that Enceladus appeared to have something like an atmosphere that was distorting the magnetic field of the planet in the vicinity of the moon. Cassini was sent in to have a closer look, and in the words of project scientist Linda Spilker, the discoveries ‘changed the direction of planetary science’.
This tiny moon, in the frozen outer reaches of the Solar System, a billion miles away, appears to possess a deep oceanic environment very similar to that on our planet 4 billion years ago.
The photographs below were taken by Cassini in October 2015 as it swept low over the surface of Enceladus. The spectacular plumes are made of water, erupting from the surface at 800 miles an hour. They emerge from hot spots on the surface known as the tiger stripes, shown in the photograph on here. The ejected material forms the majority of Saturn’s outermost ring, known as the E-ring. When Cassini flew through the E-ring, it detected the presence of silica nanograins, which are formed when water interacts with rock at temperatures above 90 degrees Celsius. The plumes themselves are rich in organic molecules, including carbon dioxide, and recent analysis confirms that they are alkaline. Precision measurements of Enceladus’s orbit suggest the presence of a subsurface ocean below the South Pole of the moon, perhaps 6 kilometres deep. Bringing all the evidence together, it appears that there is an active hydrothermal vent system on Enceladus, driving plumes of water, rich in organics, out into space. The search is now on for traces of hydrogen in the plumes, which would suggest even more strongly that Enceladus has all the conditions believed to be necessary for the spontaneous emergence of life.
The ice fountains of Enceladus, photographed by Cassini on her final flyby of the Moon in October 2015.
We need a dedicated mission to Saturn to answer these questions, and if it were up to me, I’d start building the spacecraft tomorrow.
This tiny moon, in the frozen outer reaches of the Solar System, a billion miles away, appears to possess a deep oceanic environment very similar to that on our planet 4 billion years ago. If this is correct, and if life is close to inevitable in such conditions, then might we expect to find signs of biology in the plumes of Enceladus? We must pose a question, rather than make an assertion, because there are many variables that we don’t understand. How long has Enceladus been active? Could the ocean be a temporary phenomenon, driven by the details of her orbit today, which may well have been different in the past? We need a dedicated mission to Saturn to answer these questions, and if it were up to me, I’d start building the spacecraft tomorrow, because the ice plumes of Enceladus provide us with access to the chemistry, or biochemistry, of an alien subterranean ocean. We don’t even have to land.
The ice fountains of Enceladus, erupting from the South Pole.
I think this is of overwhelming importance. We may never understand how the Universe began, but we are close to understanding how we began. This is surely one of the most profound questions of this or any age, as evidenced by the repeated incursions into the territory by philosophy and theology. But the origin of life is a scientific question, and not a metaphysical one. As Haldane wrote in ‘The Origin of Life’:
‘Some people will consider it a sufficient refutation of the above theories to say that they are materialistic, and that materialism can be refuted on philosophical grounds. They are no doubt compatible with materialism, but also with other philosophical tenets. The facts are, after all, fairly plain.
‘The question at issue is: “How did the first such system on this planet originate?” This is a historical problem to which I have given a very tentative answer on the not unreasonable hypothesis that a thousand million years ago matter obeyed the same laws that it does today.’
Almost a century on, we know much more about the historical problem than Haldane. We have precise dates for the origin of life on Earth, and a strong candidate for its incubator. We can see how geology might have become biology, and we understand how biological systems, over billions of years, can become sophisticated enough to inquire about their own origins. Can it really be true that the chemical elements, given an ocean, a vent and 4 billion years, can come to understand themselves? I think we are close to an answer.
A travel poster created by the NASA Jet Propulsion Lab extols the virtues of tourist travel to distant worlds.
Then again, since this chapter has a somewhat gothic feel, I think it should end with a hollow laugh, or perhaps the music from Roald Dahl’s Tales of the Unexpected. Let me leave you with a memory I have of a short story by Arthur C Clark called ‘The Nine Billion Names of God’. In it, the monks at a Tibetan monastery commission a giant supercomputer to compile a list of all the possible names of God. This, the monks suggest, is the purpose for which the human race was created. They are to know their creator in every detail. The engineers, with a wry smile, sell the monks the computer, install it, and leave the monastery after dusk to head down the mountain. Should be finished about now, says one of the engineers, but his colleague is silent. ‘Overhead, without any fuss, the stars were going out.’
The surface of Enceladus, showing the ‘tiger stripe’ geological features associated with the water plumes.
1 Elizabeth A. Bell, 14518–14521, doi: 10.1073/pnas.1517557112
2 Strictly speaking we should say that this is true only in equilibrium.
Two Voyager spacecrafts were launched from Cape Canaveral on 20 August 1977. It was Voyager 1 that took the iconic image of the Earth known as the Pale Blue Dot.
Pale Blue Dot
There is a picture of us all;
a point of light in the dark. This is the Earth, viewed from the Voyager 1 spacecraft on 14 February 1990 from a distance of 6 billion kilometres. The radio waves carrying the image took five and a half hours to make the journey home.
The Voyager missions were launched in 1977 towards the gas giant planets Jupiter and Saturn, with the possibility of a continuation outwards to Uranus and Neptune afforded by a once-in-a-175-year planetary alignment. Voyager 2 reached Neptune in the summer of 1989. The spacecraft’s parting glance at the frozen blue planet and her moon, Triton, is one of my favourite photographs. Delicate crescents in the dark at minus 240 degrees Celsius. Cold silence unseen for 4.5 billion years, captured once by a car-sized explorer from Earth. I have no idea when, if ever, this view will be enjoyed again.
‘What beauty. I saw clouds and their light shadows on the distant dear Earth... The water looked like darkish, slightly gleaming spots... When I watched the horizon, I saw the abrupt, contrasting transition from the Earth’s light-coloured surface to the absolutely black sky. I enjoyed the rich colour spectrum of the Earth. It is surrounded by a light blue aureole that gradually darkens, becoming turquoise, dark blue, violet and finally coal black.’
– Yuri Gagarin
Voyager 1 took a different path, flying close above the cloud tops of Titan, Saturn’s giant moon, on 12 November 1980. The flyby catapulted the spacecraft upwards out of the plane of the Solar System on a journey into interstellar space. For a decade, Voyager 1 flew away from the Sun at a speed of 17 kilometres per second, until Carl Sagan persuaded NASA to swing the spacecraft’s cameras around one last time to take a family portrait; a farewell snapshot of her home solar system as she left for the stars. Thirty-two degrees above the ecliptic plane, Voyager 1 returned a mosaic of sixty frames. Neptune, Uranus, Saturn, Jupiter, Venus and Earth are all there; only Mercury and Mars were unseen. Earth is a crescent, a tenth of a pixel in size, suspended by pure coincidence in an ochre ray from the Sun scattered in the camera’s optical system.
The Pale Blue Dot, taken by the Voyager 1 spacecraft on Valentine’s Day, 1990. Twenty-six years later this image stands as a potent symbol of our isolation, our rarity and our value.
Carl Sagan named this photograph ‘Pale Blue Dot’ and turned it into one of the most valuable images in history, with a powerful piece of writing of the same name.
‘Our planet is a lonely speck in the great enveloping cosmic dark. In our obscurity, in all this vastness, there is no hint that help will come from elsewhere to save us from ourselves.
The Earth is the only world known so far to harbor life. There is nowhere else, at least in the near future, to which our species could migrate. Visit, yes. Settle, not yet. Like it or not, for the moment the Earth is where we make our stand.
It has been said that astronomy is a humbling and character-building experience. There is perhaps no better demonstration of the folly of human conceits than this distant image of our tiny world. To me, it underscores our responsibility to deal more kindly with one another, and to preserve and cherish the pale blue dot, the only home we’ve ever known.’
Carl Sagan
‘As we begin to comprehend that the Earth itself is a kind of manned spaceship hurtling through the infinity of space – it will seem increasingly absurd that we have not better organized the life of the human family.’
Hubert H. Humphrey, Vice President of the United States, 26 September 1966
‘When you’re finally up at the Moon looking back on Earth, all those differences and nationalistic traits are pretty well going to blend, and you’re going to get a concept that maybe this really is one world and why the hell can’t we learn to live together like decent people.’
Frank Borman, Apollo 8, Newsweek magazine, 23 December 1968
If you are the sort of person who likes to overcomplicate things – perhaps the abrasive weathering of accumulated disappointment has exposed your banded cynical formations? – then you may find this naïve. I have had my share of weathering, but I think Sagan’s observations are unchallengeable. Our planet is vanishingly small in the vastness, which implies that each of us is also vanishingly small. We must come to terms with being of no cosmic significance, and this means jettisoning our personal and collective egos and valuing what we have. We can no longer assume the platform of gods, or dream of a unique place in their hearts. Science has forced us to look fixedly into an infinite universe, and its volume dilutes special pleading to a vanishingly small and pathetic whimper. And yet what’s left is better. No monument to the gods is as magnificent as the story of our planet; of the origin and evolution of life on the rare Earth and the rise of a fledgling civilisation taking its first steps into the dark. We stand related to every one of Darwin’s endless, most beautiful forms, each of us connected at some branch in the unbroken chain of life stretching back four billion years. We share more in common with bacteria than we do with any living things out there amongst the stars, should they exist, and they are more worthy of our attention. Build cathedrals in praise of bacteria; we are on our own, and as the dominant intellect we are responsible for our planet in its magnificent and fragile entirety.
A test model of the Voyager spacecraft. Through their successful capturing of high-quality images and data they have gifted their creators humility, awe and curiosity.
If this sounds hopelessly hippy, ask yourself who else might be considered responsible? Sagan is right, astronomy is humbling, and humility is the first step towards forging a better and a more secure future. Voyager’s gift to its creators, delivered in a final glance, is humility, from which responsibility follows. Humility, awe and curiosity in the face of nature are the province of science. We must accept that science has forced us to grow up, and that is a rich and fulfilling position for the human race to find itself in.
The planets are dots in Voyager’s mosaic, but they are not featureless. Their shapes and sizes may be beyond the resolution of Voyager’s 1970s tube television camera, but there is information in the few photons that made it through the lens. If there are living things out there beyond the two Voyagers, sophisticated and enlightened enough to do science, what could they make of our Pale Blue Dot? They would have only light, but light can carry information across interstellar distances if you know how to decode the messages it contains. The colours of a world are an encrypted database carrying the fingerprints of its constituents and chemistry. Understanding the physical nature of light and the mechanisms by which it is emitted and absorbed allows for the information to be extracted.
The Family Portrait, captured by Voyager 1, shows a mosaic of planets in our Solar System – Jupiter, Earth, Venus, Saturn, Uranus and Neptune – only Mercury and Mars were not visible from the spacecraft.
In this chapter we’ll explore what we know about light and its interaction with matter, and how astronomers are taking the first steps to search for life beyond the Solar System by studying the light reflected and absorbed by the pale dots around distant stars. We’ll also follow a parallel path; the study of light, motivated by curiosity alone, has led to discoveries over a thousand years that are both useful in a utilitarian sense and fascinating on a purely intellectual level. The simplest questions about the origin and nature of light and its interaction with matter are still delivering exotic answers today at the edge of our knowledge, and this is precisely where we should be. If, together, we can learn to gaze at the lights of the night sky with excitement and joy and curiosity and with no fear of the infinite unknown, we will have chosen a future free of superstition, driven by the quest for an ever-deeper understanding of nature, freed from the shackles of absolute certainty, save for the recognition of our absolute responsibility for our planet and ourselves.
We stand related to every one of Darwin’s endless, most beautiful forms, each of us connected at some branch in the unbroken chain of life stretching back four billion years.
The rainbow connection
Where do the colours of the world come from? The Earth has no lig
ht of its own, at least, not if we neglect the electric glow of our civilisation. The Pale Blue Dot is a reflector, a mote of dust catching the rays of the Sun. The Sun’s light isn’t inherently blue; it contains all the colours of the rainbow. Of course it does, it’s one of the first things we learn at school. Yet common knowledge is often hard-won. The early development of our scientific understanding of light is intertwined with the question of the origin of rainbows, and this doesn’t surprise me.
Let’s chant the glories of Surya, whose beauty rivals that of a flower. I bow down to Him, the radiant son of Saint Kashyapa, the enemy of darkness and destroyer of every sin.
– A prayer of Chhath Puja
Rainbows are amongst nature’s most intriguing regular forms, a glorious arc on elemental days. They appear above all landscapes on Earth, at any time from dawn until dusk, and yet all share a set of universal properties: the colours always appear in the same order, no matter what the weather. Red points skywards, blue to the ground. They are always centred on the observer, a personal universal phenomenon, and all arc across the sky subtending the same angle between the bright rays of the Sun and the eye of the observer: 42 degrees. A bridge to heaven or a covenant from the gods, such a magnificent symbol demands a divine explanation. And if we allow ourselves for one last time to define the divine as the underlying laws of Nature, then the rainbow is one of the most vivid shadows of the deeper structures that govern the Universe; a visual representation of the behaviour of light. This is why many of the scientific greats have tried to understand them.
Forces of Nature Page 18
