If you're seeing this message, it means we're having trouble loading external resources on our website.

If you're behind a web filter, please make sure that the domains *.kastatic.org and *.kasandbox.org are unblocked.

Main content
Current time:0:00Total duration:13:08

Video transcript

in the past 40 wonderful weeks together we've explored all of the fundamentals of biology from the tiny little machines that make us work to the systems that power the most awe-inspiring and most complex organisms on earth now I want to take our learning to the next level simply by broadening our perspective that's solid understanding of biology at the small scale under our belts it's time for the long view for the next 12 weeks we'll be learning how the living things that we've studied interact with and influence each other and their environments it's the science of ecology the idea of an organism interacting with its environment may sound simple but it's actually pretty marvelously complicated nothing escapes the long arm of ecology life influences the chemical makeup of the atmosphere the geology of the planet the climate and nothing impacts life on Earth today more than humanity does and so we're going to be exploring that relationship between mankind and our environment in a lot of detail in the coming weeks life is powerful and in order to understand how living systems work you first have to understand how they originated and developed and diversified over the past 4.5 billion years of Earth's history the principles that you hear about here today will form the framework of our next 12 weeks together get ready for the epic drama that is the history of life on Earth earth is like a cheap rental house in a college town there's always somebody living there but tenants are always moving in and out new tenants moving in the old ones rooms and sometimes the electricity gets turned off because nobody paid the power bill pretty much just chaos and like a rental house the earth isn't invincible I mean a good semester of back-to-back frat parties can tear a house up pretty fast and then you know everybody gets evicted and some new tenants move in which gives you a little bit of perspective on humanity's position as the current dominant species on the planet there have been others before us and there will probably be others when we're gone has to saw the planet rolls but it's taken eons for the earth to get the way that it is today earth formed about 4.6 billion years ago and for a while it was just chunk of rock circling the Sun suffering collisions with other chunks of rock generating unreal amounts of heat eventually the constant Smashing slowed down a little bit and the outer layer of the earth cooled but the core of the planet remained hot like really hot as hot as the surface of the Sun it gives you some idea as to how much energy and radiation contributed to the Earth's formation when you consider that four and a half billion years later there's still molten stuff in the middle of our planet and it's that inner heat that makes the Earth's surface so dynamic the planet's insides been continually bubbling up destroying what's there renovating and rearranging furniture it's this constant renewal that's part of what makes life here possible and this given things that didn't actually take life very long to show up on that hot rock about 4.4 billion years ago the planet was still getting pelted with giant chunks of rock and ice left over from the formation of the solar system there was no oxygen in the atmosphere and volcanoes were firing off all over the place but it was finally cool enough for some of the water in the atmosphere to turn from the vapor into liquid the first seas formed and in them and in the atmosphere a soup of chemicals nitrogen nitrogen oxides carbon dioxide methane ammonia hydrogen hydrogen sulfide all those things that with the help of heat and lightning and who knows what else eventually created small organic molecules in some way somehow life happens we don't know how it happened that wish we did but we don't the first life on Earth probably wasn't even life as we think of it it was just a collection of chemicals surrounded by a membrane because phospholipids as you may remember spontaneously form bilayer membranes in water over time some of the chemicals inside these membranes developed into amino acids and eventually RNA the nucleic acid that was probably the first genetic material these collections of chemicals trapped within membranes called proto BionX most likely began to grow and split and replicate themselves until some crazy copying error gave way to DNA nucleotides which is a way more stable repository for genetic information because it's double-stranded not single-stranded like RNA and once these little guys had DNA they were on their way they might have only been one cell and they were probably living in the equivalent of a hydrothermal vent but they were making the most of it so the first living things were prokaryotes single-celled organisms with no nuclei that were probably pretty similar to the archaea that we find living today in hydrothermal vents sulfur hot springs and oil wells and I apologize for pronouncing archaea wrong for the entire biology series my bad these prokaryotes probably made their grand entrance between 3.9 and 3.5 billion years ago during what is known as the Archaean Eon this is the first of what scientists would identify as 3 eons in Earth history the Archaean the Proterozoic and the Fenner azoic the Cenozoic being what we've been experiencing for the last half billion years or so an eon as you might expect takes freaking forever the first one went on for 2.5 billion years so we break up the eons into eras periods in epochs which are organized by the big deal events that we can see in the fossil record so from 3.5 billion years ago until about 2.1 billion years ago these prokaryotes were all alone on earth dead something weird happened the amount of oxygen in the atmosphere suddenly shot up basically from none to 10% in a very short period of time geologically speaking this oxygen was most likely produced by a brand-new prokaryote called cyanobacteria which had figured out how to make its own food through photosynthesis the more cyanobacteria were out there the higher the atmospheric concentration of oxygen became this oxygen revolution as it's called probably spelled DWM for a lot of prokaryotes out there that had evolved without oxygen and this was also one of the first real game changers for life on Earth because it was the first major instance of living things bringing massive change to their own environment in fact maybe the earliest sample of the ecology at work cyanobacteria changed the atmosphere judo chopped the competition and made way for the evolution of living things to take a new specific direction then about 2.1 billion years ago a new kind of organism made its big debut eukaryotes these as you know are a big deal because they include all plants and animals carry oats probably evolved by a process called endosymbiosis where one prokaryote parasitized another prokaryote or maybe just ate it but forgot to digest it and the result was actually really awesome for both the host and the parasite / undigested prey it formed a single-celled organism with organelles specifically mitochondria and plastids which probably evolved from those eaten or parasitic prokaryotes this allowed for much more complexity and by 1.5 billion years ago we start seeing multicellular eukaryotic organisms in the fossil record the very first of them probably being algae but it wasn't until around 535 million years ago that the eukaryotes went berserk and that's known as the Cambrian explosion a super major biological golden age when the diversity of all animal life on earth exploded nobody's entirely sure what started it but suddenly life created innovations that the planet had never seen creatures used minerals and seawater to build skeletons and shells some acquired weapons like claws while others develop defensive plates the evolutionary arms race between predators and prey was underway this heralded the dawn of the phanerozoic eon the one that we're in right now that's right the earth spent the better part of two eons under the rule of a bunch of archaea and bacteria and some like soft bodied worms until the Cambrian exploded and we started to see a lot of animal phyla that we actually are hanging out with the day after the Cambrian the party got so hot in the oceans that by the Ordovician period around 500 million years ago plants animals and fungi started colonizing land probably as a strategy for escaping predation now there were a whole new ecosystems to explore and adapt to and create during the Devonian period about 365 million years ago tetrapods four-legged vertebrates that probably evolved from lobe-finned fishes showed up on land and sort of arthropods like insects and spiders from here we begin to see ecological systems that we recognize today because organisms were changing they're in remnants by consuming oxygen in the atmosphere and releasing carbon dioxide and you know who likes carbon dioxide the plants the Carboniferous period that extended from 359 to 299 million years ago was when the plants entirely went nuts the forests were so dense and so widespread that they made all our fossil fuels all the coal and oil that we now used to power all the things with were made over the course of about sixty million years this time it was the plants that had changed both the climate and the geology of Earth these forests cranked out so much oxygen that the atmosphere contained around 35% oxygen rather than today's like 21% all this oxygen started cooling the planet because there wasn't enough carbon dioxide to maintain the balmy temperatures that the vast Carboniferous jungles needed to survive so the whole system crashed and all the carbon from these forests sunk into swamps and eventually got locked in rocks of course now we're releasing all that carbon by burning fossil fuels which is certainly helping to keep the planet toasty now that right there some good ecology in the Permian period 299 251 million years ago all the land masses of the world joined to form one giant continent that we call Pangaea altering global climate and ocean currents and animals and plants evolved in response we start seeing gymnosperms the first plants with seeds like modern pines and spruces and firs and ARCA soars the granddaddy's of dinosaurs and modern birds showed up but you probably picked up enough of the pattern here to predict that this party didn't last forever about 252 million years ago something happened or maybe a lot of things happen in quick succession but whatever they were movie executives take note the Permian Triassic extinction event would make the most awesome disaster film of all time because up to 96 percent of all marine species and 70% of terrestrial vertebrate species bought the farm and it's the only known mass extinction of insects about 57% of all taxonomic families and 83% of all general became extinct it was the most significant extinction event on the planet ever it's been hard to pinpoint the reason for this extinction event because most of the evidence have been wiped out of course it may have been kicked off by an asteroid that released the energy equivalent to the detonation of a few million nuclear weapons all at once and then insulated to injury when a whole bunch of volcanoes erupted methane was released from the seafloor there were probably some gas explosions and what's now Siberia and then a whole bunch of climate changes sea level change and changes in ocean salinity probably occurred nobody sure exactly what happened but we do know that it took a long time for life on earth to make a comeback look at the bright side as a result of the Permian Triassic event we got dinosaurs they were able to evolve during the Triassic because there wasn't much competition for resources so they evolved to fill an available niche that is a combination of living and nonliving resources that they could use to survive remember that word because a lot of ecology comes down to who's exploiting or leaving or getting kicked out of or altering their niches and during the Triassic period there were tons of niches the sky was the limit because they there weren't very many animals or plants to compete with so by the Jurassic period about a hundred and ninety nine million years ago - 145 million years ago huge herbivorous dinosaurs were roaming the earth smaller meanest crap carnivorous dinos were stalking the herbivores the oceans were full of giant squid and Ixia sores and long-necked plesiosaurs the air was full of pterosaurs in the first Birds and there were mammals small ones but they were all over the place it just wasn't our time to shine the Jurassic was Dino time and the dinos lived it up they partied down until about 65 million years ago when they all went extinct as I'm sure you're aware except for their surviving descendants the birds was probably an asteroid that hit the Yucatan Peninsula in Mexico that did the men but other theories suggest it could have been climate change due to increased volcanic activity and the possibility that they just couldn't adapt to changes and other living things around them for instance about a hundred million years ago angiosperms or flowering plants first appeared and they did really well especially since flying insects evolved with them providing a great vehicle for reproduction this is a great example of another eka logical principle coevolution the dinosaurs like to eat the old-fashioned gymnosperms we know that from studying their fossilized poop so maybe their pickiness made them go extinct who knows and with the dinos out of the picture mammals and birds were free to take over and this is where the flora and fauna on planet Earth start looking a lot more like they do today since then there have been climate fluctuations and extinction events and the evolution of many animals and plants including humans and on logical scale oddly enough that kind of brings us up to today ecology is all about action and reaction and asteroid hits and a bunch of stuff happens because of it plants take over and different stuff happens because of that humans start releasing all the carbon dioxide locked in 300 million year old rocks and the planet heats up and you know we don't know what happens but ecology is providing us our best guesses over the next three months we're going to explore these relationships and more and more detail as well as like how humans relate to the whole thing and how we're affecting all of this
Biology is brought to you with support from the Amgen Foundation