What Would The Earth Have Been Like Without Life?

[Music] on valentine's day 1990 a camera shutter clicks [Music] every photograph is unique but the image captured at this particular moment is unlike anything that's been seen before or will be seen again for many years to come it is of the earth from 6 billion kilometers away the last glimpse of home for the voyager 1 space probe venturing into the darkness never to return voyager 1 has been on a grand tour of the outer solar system since its launch in 1977 it's flown past and photographed jupiter and saturn before heading out into interstellar space but before it leaves its onboard cameras capture a family portrait of six planets including the earth it beams back the images encoded in radio signals traveling at the speed of light the signals take five and a half hours to reach us it's the last photo the probe takes before its cameras power down forever this photo of the earth is not what you might expect diagrams of the solar system rarely show the planets and their relative distances to scale in voyager 1's image made up of 640 000 pixels our planet takes up less than one in this picture earth is nothing more than a pale blue dot this fraction of a pixel contains every living thing that we know of from bacteria to blue whales it contains endless marching forests and grassy savannah it contains more than 5 billion people and their sprawling cities on almost every continent but from this far away all of this life is invisible earth is a pale blue dot a blur of deep blue oceans and white clouds from this far away our home appears as empty as the barren planets in our solar system family [Music] but is this really true is the evidence for life on our planet so easily masked by mere distance would our home pixel really look the same if life had never come about in the first place [Music] on earth today living things surround us they're in the rocks in the air in the oceans the planet is teeming with life but as far as we have yet discovered this is a rarity in the cosmos is life really so unlikely in 1953 german-born physician hubertus stroghold was contemplating the medical challenges of space exploration when he coined the term ecosphere the ecosphere is a habitable zone around a star in which conditions are sufficiently temperate for life to thrive by venturing away from the ecosphere astronauts would find it incredibly hard to survive by definition earth sits within the ecosphere or habitable zone around our star but since struggle's revelation astrobiologists worldwide have tried to identify the criteria for a planet to become home to living things of course these criteria are based on what we know about terrestrial life and basic chemistry that's the best we can do with a sample size of one first the star must be suitable it must be long enough lived to allow planets to orbit with stable conditions for a few billion years out of all the stars in our galaxy about 90 percent make the grade then the star must have rocky planets orbiting around it solid surfaces help the chemical reactions of life so although it's possible for living things to be entirely airborne it is much more likely that life got started on a solid rocky surface not only that but in order to sustain life's chemistry the planet needs liquid water on its surface and an atmosphere that is neither too thin nor too thick and crushing to have a planet of just the right size orbiting within the habitable zone of its star where it's the right temperature for water to linger as a liquid is incredibly rare scientists estimate between five and fifty percent of sun-like stars will have a planet like that still in our galaxy alone that leaves the potential for several billion planets just like the earth is life on these planets inevitable unfortunately that's not an easy question to answer we just don't know enough about the early conditions on earth and the chemical revolutions that led to the first life we don't know if given the right mix of chemicals life sprang up spontaneously all over the globe or if it took a remarkable stroke of luck in one isolated pool in one corner of the planet with this huge unknown we can't say if life is assured or if it's one in a billion but since the origin of life still eludes us there's a good chance that it's not easy or inevitable dedicated scientists still haven't recreated those earliest living things from non-living matter so maybe life on earth was in fact a fluke [Music] if life on earth came about because of a lucky roll of the chemical dice then it's much more likely that it never started at all how then would the planet have evolved over 4 billion years without life how different would it look today people no cities no birds in the sky no fish in the sea no crawling insects no plants no trees no grassy savannah no mossy rocks no seaweed on the shore far from a world dorbed liberally with green we'd be faced with a hard harsh landscape of gray rocks and dark blue oceans but the absence of life goes much deeper than what we see on the surface in fact some argue that there's nothing at all on our planet that hasn't been affected by living things the surface itself is sculpted by life plants from the most basic lichens to the biggest trees are routed to the land surface and modify it in turn root systems probe into the finest cracks take hold and tear solid stone into shattered debris water penetrates the surface of this new rubble dissolving minerals which the plants absorb in this way the compositions of the rocks at the surface are permanently altered by biological weathering the result is a new kind of material which wouldn't exist at all without life soil as well as the weathered rocks soils contain an abundance of organic matter too both living and dead so if life never evolved on earth there'd be no soil on the surface today instead the land surfaces of earth might look more like those on the dusty red planet mars although soils may seem like a minor loss from our planet this thin layer has had a major effect on the shape and longevity of surface features because up to 50 percent of a soil is made up of voids empty space which can be filled with water that helps the rock fragments and organic matter stay stuck together combined with the root systems that form them in the first place soils are incredibly good at staying put and protecting the unweathered rocks beneath them without soils we could say goodbye to rolling hills and valleys the landscape would be a hard harsh one of craggy mountains deep gorgeous and chaotic rock falls and landslides altered by vast tectonic forces and the inexorable grind of water wind and ice the rocks exposed at the surface would be fundamentally different too if life had never arrived there would be no fossil shells or bones no coals oils or natural gas either around 10 percent of rocks exposed at the surface today are limestones formed from calcium carbonate which almost always has been created by living things mollusks corals and tiny plankton all make their shells from calcium carbonate without life there would be no white chalk cliffs of dover or marble quarries of the italian dolomites but it's not just the solid surfaces of earth that life has transformed living things have fundamentally altered the planet's swaddling atmosphere too before any life arrived on the early earth the atmosphere was a concoction brewed in the belly of a volcano carbon dioxide water vapor and methane all spewed from the hellish molten landscape of the hadian but life and especially green life changed all of that photosynthesis which transforms water and carbon dioxide into sugar and oxygen using light as an energy source was a revolution for the earth's atmosphere this new chemical pathway was seized with further by living things about two and a half billion years ago the carbon dioxide that was so abundant in the early atmosphere was a bottomless feast for the first green organisms they absorbed it and excreted oxygen in its place and then they absorbed some more to build their shells creating limestone rock and so the atmosphere transformed from one dominated by carbon dioxide and methane to one rich in oxygen instead had life never gained a foothold and figured out photosynthesis our atmosphere would be the same steamy volcanic effusion that reigned in the hadian dominated by physical processes and spontaneous chemical reactions and indeed today a visitor to a lifeless earth would find an almost unrecognizable planet with a palette of colours closer to venus or saturn's moon titan than the blues and greens and whites gifted us by life without oxygen in the air it's not available to react with surface rocks and sediments much of the red color we see in dunes and in river deposits is a result of iron minerals reacting with oxygen to make iron oxide or rust without life to make the oxygen to make the iron oxide the surface of the planet would be painted in little more than shades of grey without reactive oxygen methane can stick around in the atmosphere too and when sunlight hits methane it makes hydrocarbons not enough for life but enough to make a sickly orange haze that fills the atmosphere with a permanent smog all over the surface of the earth the sun would be veiled as if by some approaching wildfire or distant volcanic eruption incredibly a lack of life also means a lack of clouds too the tiny creatures whose calcium carbonate shells make up the white cliffs of dover also emit chemicals into the air that helps water condense into droplets and make clouds they're so abundant in the oceans that they're a major contributor to our cloud cover without them the planet may never be graced with the wisps of white cirrus or banks of fluffy cumulus instead only an indistinct humid fog would lie heavy beneath the overlying methane smog in fact had life never modified our atmosphere the earth may have suffered a similar fate to our planetary neighbor venus carbon dioxide is a greenhouse gas trapping the sun's heat close to the surface with an atmosphere full of this potent insulator surface temperatures gradually rise until they reach truly hellish levels the surface of venus bakes at more than 450 degrees celsius due in part to its thick blanket of co2 that could have been the earth without life it seems we may have life itself to thank for keeping our planet livable [Music] curious reliance of our planet's habitability on its living inhabitants was a paradox first noted by english scientist james lovelock in the 1970s lovelock is something of a contemporary polymath having worked in medicine chemistry and environmental science in the 1960s he considered how life might be detected on mars one of the most promising signatures lovelock concluded was non-equilibrium only life has the power to drive atmospheres away from chemical equilibrium just as on earth reactive oxygen came to replace carbon dioxide finding an atmosphere out of balance suggests an invisible hand at work by extension he noted how the conditions on the earth influence its biosphere and how living things have the power to affect the earth itself on a long-term global scale the result he saw was a self-regulating system that keeps conditions stable and suitable for life all over the planet a super organism of sorts on a planetary scale he named his theory of a protective self-sustaining feedback loop after the greek goddess of earth gaia and lovelock's gaia works in many different ways to unconsciously keep the earth habitable to demonstrate the power of a self-preserving planetary superorganism lovelock and others conceived of a computer simulation of a theoretical planet which is home to two populations of daisies black daisies and white daisies it was called daisy world black daisies liked it when it was cooler and white daisies when it was hot in the planet's early days when the heat from its young sun was weak the black daisies thrive and cover the planet their dark colour helps to absorb the sun's heat soon it becomes warm enough for white daisies to take over their bright colour reflects rather than absorbs the sun's energy and the planet temperature drops black daisies take over again and eventually an equilibrium is reached with both black and white daisies helping to keep the planet's temperature optimal for both populations daisy world is an incredibly simple model of a planetary feedback loop and the earth is certainly a much more complex system but similar feedback loops have been affecting conditions on the planet over geological time scales take for example the carbon dioxide in our atmosphere volcanoes emit carbon dioxide causing levels of the gas to rise in the atmosphere and increasing the thickness of our warming blanket of gas temperatures rise warm temperatures are good for life in general one need only to look at the tropical rainforests to see how living things thrive when it's warm so when the earth is warmer plants grow faster and denser and all these plants need carbon dioxide to fuel their photosynthesis so they draw it down from the atmosphere and lock it away in their tissues some is returned to the atmosphere but much of it is sequestered away in the long term in other living things or in soils or in the rocks themselves by reducing the amount of carbon dioxide in the atmosphere and thinning the blanket of greenhouse gas living things have ensured that the earth doesn't get too hot and there's a check at the other end of the scale too if carbon dioxide levels drop too low the earth's temperature will also drop colder ice-covered landscapes aren't hospitable to life so plants don't thrive there aren't large populations to hoover up carbon dioxide so over time the gradual input from volcanoes can boost levels until temperatures start to rise again in this way carbon dioxide levels and temperatures have fluctuated through much of earth's history moderated by living things regulation by the guiding hand of gaia never sees conditions pushed too far and guys mechanisms don't just see temperatures maintained the complex interaction of organic life with the inorganic earth helps to keep the chemistry of our oceans in check too helping salinity and acidity stay at the same levels for hundreds of millions of years gaia's guiding hand has no consciousness behind it it is but a fortunate consequence of our life's colonization of earth it's this link that has kept earth habitable and inhabited for billions of years an ecosystem that doesn't promote the conditions of its own survival is not destined to last long [Music] and yet in the last hundred years or so humans as the newest life form on the scene are testing gaia's ability to bounce back the changes that we have wrought on our planet have been faster and more extreme than anything gaia has yet faced carbon dioxide levels have risen and global temperatures have soared it remains to be seen whether our ecosystems can adapt to compensate in time before the planet [Music] roasts when voyager 1 pointed its cameras back at the earth in 1990 it saw a blurry pale pixel the life that graces our planet is invisible from 6 billion kilometers away but its effects on the globe are not that our oceans and clouds persist at all is a sign that temperatures are still optimal for surface water and that is thanks to life and gaia next time we will explore the fascinating stories behind the first fossils and the origin of earth's magnetic field [Music] you've been watching the entire history of the earth like and subscribe and we'll see you again soon

Channel: History of the Earth

Views: 468,090

Rating: 4.9037375 out of 5

Keywords: space, earth science, geology, first life, solar system, science, history of earth, entire history

Id: QbJGum0sWYE

Length: 21min 25sec (1285 seconds)

Published: Wed Sep 02 2020