Life

by Tim Flannery

  We have a reasonably concise date for the formation of Earth—4560 million years ago, give or take 10 million years. The half a billion years that followed, known as the Hadean Eon, were momentous. A huge asteroid slammed into the planet, forming the moon and transforming Earth into a ball of molten rock. As Earth cooled, the progenitors of the modern core and crust were formed. Earth’s oldest rocks—tiny, 4.4-billion-year-old zircon crystals from Western Australia—are the only physical evidence we have of this period. Chemical analysis reveals that they formed where ocean water was being sucked down into the mantle—the layer of the earth between the crust and the core. So we can surmise that Earth cooled quickly after the asteroid collision, and that at an early stage it had oceans.

  Despite the presence of oceans, Earth was almost certainly hostile to life in the Hadean Eon. Asteroid impacts repeatedly shook the planet, boiling its oceans and changing the atmosphere. But by four billion years ago, things had begun to settle down. The 1.5-billion-year-long Archean Eon had begun, and it was over the first third of this period that the nanomachines either evolved, or as Ward and Kirschvink argue, colonised Earth from elsewhere.

  As we ponder life’s origins, Ward and Kirschvink warn against thinking in simplistic terms like life and death, instead encouraging us to consider the ‘newly discovered place in between’. Life’s most distant origins lie in the non-living precursor molecules for RNA, organic compounds known as amino acids. They have been found in meteorites, are presumed to be widespread in the universe, and their origins must greatly predate Earth’s origins. The nanomachines possess attributes of life, and when brought together in a cell they clearly cross the threshold into the self-regulating, replicating entity that we recognise as a living thing.

  A slick layer of graphite preserved in 3.8-billion-year-old rocks near Isua, Greenland, was long believed to contain the earliest evidence of life on Earth. But recent studies reveal that the carbon composing the graphite was not formed by life at all. The next oldest evidence was long thought to be 3.5-billion-year-old microscopic fossils of algae from Western Australia. But recent research has shown that the ‘fossils’ are far more recent, and in any case may not be fossils at all, but crystals. A 2012 study announced that fossils of bacterial ecosystems dating back 3.49 billion years had been discovered in the Pilbara region of Western Australia, and this is now widely accepted as the oldest evidence of life.2

  Charles Darwin famously speculated that life began in a ‘shallow, sun-warmed pond’. But back when Earth formed, its surface was probably covered entirely, or almost so, by oceans. And because Earth lacked an ozone layer for the first two billion years of its existence, it is unlikely that shallow waters could have hosted life’s origin because ultraviolet radiation would have torn apart the delicate, assembling RNA.

  Currently favoured candidates for an earthly origin of life range from hot springs to mid-ocean ridge vents known as ‘black smokers’. Conditions there may have aided the formation of the ever-longer strings of amino acids and molecules, including RNA, that were eventually able to metabolise and reproduce. Mid-oceanic ridges are protected from ultraviolet radiation by the overlying ocean. They are also rich in the elements required for DNA. Additionally, the majority of the most ancient life forms on Earth are thermophiles, small organisms some of which thrive in near-boiling water. One problem for this theory is that water attacks and breaks up the nucleic acid polymers that make up RNA. And unless protected, it is also destabilised by heat.

  Most research focuses on a search for the earliest life. But perhaps we should be searching instead for evidence of the first nanomachines. Chemical signatures in rocks that result from the activities of the nanomachines offer one means of doing this. For example, studies show that the nanomachines that make atmospheric nitrogen, and can add oxygen to the ammonia so produced in order to create nitrate, were in existence by at least 2.5 billion years ago.3

  Joe Kirschvink argues that Earth’s rocks are the wrong place to look for the nanomachines’ origins. He is a leading proponent of the seemingly radical theory that the nanomachines, and perhaps life itself, originated on the ice caps and glaciers of ancient Mars. The case is fleshed out fully in A New History of Life, and recent discoveries are building an impressive body of supporting evidence. NASA’s Curiosity lander, for example, has found evidence for ancient Martian streams and ponds: billions of years ago Mars probably had an ocean, as well as land and ice caps. The red planet may have offered a far less hostile environment for assembling naked strings of RNA than Earth. Kirschvink also points out that space travel by early life is not improbable. Mars is small, so its gravity is weak compared with that of Earth. Asteroids could therefore have thrown up a lot of rocks capable of escaping Martian gravity. And we know, through experiments, that meteorites originating from Mars can reach Earth without being sterilised.

  But if the nanomachines did originate on Mars, where might they have crossed the ‘Darwinian threshold’ and become truly living things? Kirschvink argues that Earth’s atmosphere offers a plausible nursery. Held aloft by fierce winds and currents, the Martian RNA fragments may have mixed with each other, exchanging fragments from one chain to another. Natural selection would have favoured the more functionally complex and efficient strands, which would then have proliferated. Eventually, perhaps when the strands became encompassed by cell walls made of tiny droplets of lipids (a type of molecule that includes fats and waxes), the mass transfer of genes between the nascent nanomachines slowed and their chemistry stabilised.

  The Nobel laureate Christian de Duve believed that at this point life would have emerged from nonlife very quickly, perhaps in minutes. Safe behind its lipid cell walls, the RNA could enter the ocean, finding the rich trove of nutrients that exists around the black smokers. From then on, Darwinian evolution would have ensured the survival of those that operated most efficiently in a hot environment. This story is, of course, almost entirely unsupported by evidence. It is a scenario—a vision of how things might have been—rather than a fleshed-out scientific theory. It is nonetheless useful because it provides a target for future researchers.

  A New History of Life deals with life’s entire trajectory, from the time before its first spark to the present. The conventional view is that for a billion years after life first evolved, very little seems to have happened. Then, over perhaps a few hundred million years, oxygen utterly transformed the face of Earth. That oxygen came from the most complex cellular nanomachinery ever to evolve—the trinity organisms, composed of three organisms embedded within a single cell, that could photosynthesise. But Falkowski’s nanomachines make me think that the billion-year ‘pause’ before their emergence is illusory. Enormous changes to life’s engines occurred as they transformed from relatively simple nanomachines to planet-altering photosynthesisers.

  A mystery surrounds the oxygenation of Earth. The oxygen produced by the photosynthesisers should have interacted immediately with organic matter, preventing any increases in free atmospheric oxygen. And indeed this is what appears to have happened for hundreds of millions of years after the first trinity organisms evolved. What was needed, if free oxygen was to accumulate in the atmosphere, was for some of the organic matter it reacted with to be put out of the oxygen’s reach.

  Falkowski thinks that ‘the oxygenation of Earth had much to do with chance and contingencies’. Ward and Kirschvink agree, saying that one of the greatest contingencies was the creation of what we call fossil fuels. For fossil fuels and other buried organic molecules are organic matter put out of oxygen’s reach many millions of years ago, and they exist in Earth’s crust in direct proportion to the amount of oxygen in the atmosphere.

  The dependence of evolutionary change on contingencies is further highlighted when Ward and Kirschvink discuss the evolution of the first large animals. They arose about half a billion years ago, in what is known as the Cambrian explosion. Scientists have long argued about why they evolved so rapidly, and at that time. Ward and Kirs
chvink think they have an answer, in the form of ‘true polar wander’. Essentially, the idea is that as the continents moved over the face of the planet, they altered its centre of gravity. By around half a billion years ago they had so shifted the gravitational centre that the Earth’s outer layers had begun to move relative to Earth’s core. Over millions of years, the landmasses originally lying over the poles came to lie over the equator. This southward shift may have released methane trapped in clathrates (ice-methane combinations kept stable by low temperatures or pressure), triggering a release of greenhouse gases that warmed the climate and provided favourable conditions for an increase in biodiversity. There is evidence to back parts of this theory. Something odd was happening to Earth’s poles around the time complex life evolved. And ‘true polar wander’ is characteristic of other planets, including Mars. But again, Ward and Kirschvink are pushing the envelope with this theory.

  Neither Life’s Engines nor A New History of Life is an easy book for the non-scientist, but both are immensely rewarding. Like Galileo’s telescope and microscope, they focus on the very small (Falkowski) and the very big picture (Ward and Kirschvink). Both are full of novel thinking about life’s origin and subsequent evolution. Taken together, they help us begin to see where the next big questions about life’s origins lie, and how they might be investigated.

  Foreword to The Hidden Life of Trees

  2016

  WE READ IN fairytales of trees with human faces; trees that can talk, and sometimes walk. This enchanted forest is the kind of world, I feel sure, that Peter Wohlleben inhabits. His deep understanding of the lives of trees, reached through decades of careful observation and study, reveal a world so astonishing that, if you read his book, I believe that forests will become magical places for you, too.

  One reason that many of us fail to understand trees is that they live on a different timescale to us. The oldest trees on Earth are nearly 5000 years old. That’s sixty times longer than the average human lifetime. Creatures with such a luxury of time on their hands can afford to take things at a leisurely pace. The electrical impulses that pass through the tissues of trees, for example, move at the rate of one centimetre per second. But why, you might ask, do trees pass electrical impulses through their tissues at all?

  The answer is that trees need to communicate, and electrical impulses are just one of their many means of communication. Trees also use a sense of smell and taste for communication. If a giraffe starts eating an African acacia tree, the tree releases a chemical into the air that signals that a threat is at hand. As it drifts through the air and reaches other trees, they ‘smell’ it and are warned and begin producing toxic chemicals. Likewise, if the saliva of a leaf-eating insect is ‘tasted’ by the leaf being eaten, the tree sends out a chemical signal that attracts that insect’s predators. Life in the slow lane is clearly not always dull.

  But the most astonishing thing about trees is how social they are. The trees in a forest care for each other, sometimes even going to the extent of nourishing the stump of a felled tree for centuries after it was cut down, by feeding it sugars and other nutrients, and so keeping it alive. Only some stumps are thus nourished. Perhaps they are the parents of the trees that make up the forest of today. A tree’s most important means of staying connected is the existence of a ‘wood wide web’ of fungi that connects trees in an intimate network that allows the sharing of an enormous amount of information and goods. Scientific research has only just begun to understand the astonishing abilities of this partnership.

  The reason trees share food and communicate is that they need each other. It takes a forest to create a microclimate suitable for tree growth and sustenance. Isolated trees have far shorter lives than those living connected together in forests. Perhaps the saddest plants of all are those we have enslaved in our agricultural systems. They seem to have lost the ability to communicate and, as Wohlleben says, are thus rendered deaf and dumb. Their lives really are nasty, brutish and short.

  Opening this book, you are about to enter a wonderland. Enjoy it.

  Extravagant, Aggressive Birds Down Under

  2017

  TOWARDS THE END of his highly enjoyable book Where Song Began, Tim Low informs us that ‘it might be said that the world has one hemisphere weighted towards mammals and one towards birds’. The hemisphere weighted toward mammals is the northern one. And Low makes a convincing case that, in the south, birds of a most extravagant type occur. But is the southern hemisphere truly weighted toward birds? One window into the question is through bird–human interactions. We humans are used to getting our way with nature, but in the antipodes birds occasionally gain the upper hand.

  Such was the case when, in 1932, Australia decided to declare war on the emu, an enormous flightless bird whose image is emblazoned on the country’s coat of arms. Sir George Pierce, Australia’s defence minister, was beseeched by farmers from Australia’s south-west for deliverance from the ravening creatures, which were swarming out of the desert in countless thousands, driven south by drought. Sir George agreed to help, and so was sparked what would become known as the Great Emu War.

  Major C.P.W. Meredith of the Seventh Heavy Battery of the Royal Australian Artillery was ordered to proceed with armed troops to the environs of Campion, a small town located near the emu ‘frontline’. There, the army was to use Lewis guns (machine guns) to disperse the invaders. Hostilities commenced on 1 November, but the birds were at such a distance that gunfire was largely ineffective. The next day, a thousand emus were seen advancing on a dam. Meredith and his troops were in a splendid position to inflict maximum casualties, but after only fewer than twelve birds were killed the Lewis guns jammed. Frustrated by the fleetness of the birds, Meredith had the machine guns mounted on trucks, but the emus easily outran the vehicles.

  A month later, a crestfallen Meredith was forced to explain to the Australian Parliament that the war had been lost. He said of his foe:

  If we had a military division with the bullet-carrying capacity of these birds it would face any army in the world. They can face machine guns with the invulnerability of tanks. They are like the Zulus whom even dum-dum bullets could not stop.

  The war was not over, however. Irregular troops in the form of bounty hunters were enlisted, but even they could not subdue the foe, and the conflict continued for decades.

  Being defeated in war by one’s avifauna is ignominious. But Australians are inured to being stung, bitten, envenomated or outright eaten alive by a hostile fauna. Incredibly, Low claims that even Australian songbirds are dangerous. The Australian magpie looks like a very large jay, and when it breeds in the spring, it turns the country into a battleground. Magpies defend their territory by ‘dive-bombing’ ‘invaders’ from the rear, which is why you may see Australian pedestrians waving umbrellas into a clear sky, or cyclists with rearward-looking faces painted on their helmets.

  Magpies, according to Low, ‘can distinguish kindly adults from scheming boys’. Postmen are particularly detested: Australia is perhaps the only country on Earth where they fear songbirds as much as dogs. And those whom magpies particularly loathe will be identified and targeted, even if they haven’t been seen for years. Low tells of a ‘terrorised school in Brisbane’ where ‘throngs of screaming parents at the gates were trying to get their terrified children to run quickly across the open area to the main building where the school medical officer was waiting with the first aid kit’. Over two weeks, more than a hundred children had their faces cut by magpies. But the damage can be much worse. Magpies will sometimes land in front of a person they despise, and then leap at their face. Each year, one or two people are stabbed in the eyes.

  Surveys indicate that 85 per cent of Australians have been harassed by magpies, so it seems remarkable that a magpie that blinded a boy in the Queensland town of Toowoomba was relocated rather than killed. In 1856, the naturalist George Bennett said of these remarkable creatures, ‘It is a bird of much importance in its own estimation, struts abo
ut quite fearless of danger, and evinces, on many occasions, great bravery.’ It says something of the national character of Australians that they can forgive such a creature almost anything.

  Australia and New Guinea are joined at times of low sea level and share many species in common. Consequently, Low uses ‘Australia’ as shorthand for Australia–New Guinea throughout his book. The flightless cassowary inhabits the rainforests of New Guinea and north Queensland. The size of a man, its gaudy purple, yellow and red head bears a high crest and a frighteningly malicious eye. On its foot is a ten-centimetre-long dagger-like claw, which Low suspects is used to ‘kill many more people in New Guinea than tigers do in most countries in Asia’.

  I worked for twenty years in New Guinea, and am certain that Low is correct. It’s the male cassowaries that incubate the eggs and care for the chicks, and they will attack out of the blue if you go anywhere near their young. There being so very few accounts of a cassowary attack (because most happen among remote tribes living in dense jungle), it is worthwhile recounting one instance here. Professor Joe Mangi is a friend and archaeologist who told me of an attack that occurred in the 1980s in Papua New Guinea’s Southern Highlands. The victim had found a cassowary nest and was taking the eggs (which are bright green and up to fourteen centimetres long) when he heard a booming noise. He barely had time to grab his machete and leap to meet the attacking bird. They met mid-air, the man severing the cassowary’s leg, the bird disembowelling the man with its claw.