Category
📺
TVTranscript
00:01The Earth, an epic story four and a half billion years in the making, with drama and surprise at every turn.
00:13It's the story of a tiny planet, unique in the universe, because here alone, life began.
00:21Right from the get-go, the natural world has displayed a spectacular and thrilling diversity of colour, form and extraordinary behaviour.
00:35It's also the story of our own journey into being.
00:41Life evolved in the sea, on a water-bound planet.
00:46But land masses slowly appeared, and aquatic life began to explore different ways to colonise it.
00:55Invertebrates crept from the water. The first plants found ways to grow.
01:04The new resources were enough to tempt fish to take their first steps from the water, and to change the world forever.
01:15The Earth.
01:16The Earth.
01:17The Earth.
01:18The Earth.
01:19The Earth.
01:20The Earth.
01:22Four and a half billion years ago, our planet was a mass of angry molten rock.
01:28But as chemicals churned and mixed, something remarkable happened.
01:38Against the odds, chemicals and conditions collided in just the right way to spark the very first signs of life.
01:46Since that time, there has been a race for life to adapt, colonise and compete, driving evolution.
02:01Most life forms first evolved in water, but the sheer abundance and variety was driving some species to look for new frontiers.
02:16There was an unconquered kingdom.
02:21The land.
02:26The first terrestrial beings were not very impressive.
02:33Their small and fragile bodies were rarely preserved in the fossil record.
02:40And so the details of the first pioneers remain sketchy to say the least.
02:50Picture warm shallows.
02:53Coastal lagoons with sandy shores and mud banks.
02:56The Earth was barren.
03:00No animals or plants.
03:05But the seas were teeming with early life.
03:21We have yet to meet the first land animal.
03:43All that is known of it is faint trackways fossilised in sand.
03:47But the tracks suggest it was probably something like a centipede.
03:58It was a marine animal.
04:01Probably just scurrying ashore to check it out.
04:04Or perhaps to escape an aquatic predator.
04:12In the early days, there was barely any plant life.
04:15Fossils suggest a few small, simple moss-like structures here and there.
04:27From then on, progress on land was not so much a race as a crawl.
04:34In terms of known fossils, it was another billion years before new species left their mark.
04:40It was during a period of geological time known as the Silurian, from 440 to 410 million years ago, that life really got a foothold on land.
05:01Aquatic worms may have been venturing onto land for short periods for a while.
05:14But it was arthropods, the invertebrates with hard exoskeletons, that were the first to really plant their flag on dry land.
05:28The earliest known fossil is of a scorpion, some 437 million years old.
05:44In some respects, especially its cardiovascular system, it was similar to the horseshoe crab and may have had a similar lifestyle.
05:58The ancient crabs are marine, but can cope with short periods on land.
06:15Known as Parioscorpio, the fossil suggests that scorpions have barely changed over 440 million years.
06:23Several other fossils, just 10 million years younger, show other frontrunners.
06:37The ancient rocks of Scotland and eastern North America have revealed Campycaris and Pneumodesus, myriapods like centipedes and millipedes.
06:56Detail in fossils suggest that they have spiracles along their sides like the modern species to enable them to breathe oxygen from air.
07:11These multi-legged marvels have been around a long time.
07:15To transition to land from their aquatic origins, both plants and animals needed to overcome the same challenges.
07:30How to conserve water so they wouldn't dry out.
07:36How to extract oxygen from air instead of water.
07:39How to breed and how to disperse through the landscape.
07:51They had been used to having their bodies supported by water.
07:55But now they had to find ways to support their weight against the full force of gravity.
07:59The leaders in the field were arthropods.
08:20Arthropods had evolved in the water, but adaptations for that lifestyle were to come in handy on this new frontier.
08:26It's known as exadaptions.
08:32When a trait evolved earlier to solve one problem, then gives one species an advantage over another to adapt to change or a new niche.
08:43Arthropods had developed tough exoskeletons to give them both manoeuvrability and protection in the hostile seas.
08:57This gave them a leg up, literally, to set foot on dry ground.
09:01The shell was also good at retaining moisture to stop their gills from drying out.
09:17The first creatures to walk the earth were the earliest types of spiders, scorpions and centipedes.
09:30It had taken a while for animals to get a footing, but things were to rapidly change.
09:47After a mere 20 million years, there was a much greater diversity.
09:51Plants were adapting, and the planet had its first tall trees.
10:06And bugs were getting big.
10:11There were human-sized scorpions wallowing in the shallows.
10:14Why did these creatures leave the water? Nobody knows for sure.
10:24It may have been because the seas were getting crowded.
10:27Niches were full. Competition was rife.
10:31They were looking for new opportunities.
10:35Or clambering ashore may have been a way of escaping predators,
10:39going where the hungry mouths could not follow.
10:41Most of the time.
10:44Most of the time.
10:58To begin with, they were arriving on a barren earth.
11:02But each new organism became a resource and opportunity for something else.
11:07Soon there was a rush of pioneers looking to make a land grab, wanting to utilize this promised land.
11:24At the same time that arachnids and the earliest wingless insects were laying claim,
11:30there was another group with ambition.
11:31Fish were getting ready to take the leap.
11:32Again, it was ex-adaptions that paved the way.
11:47Long before fish crawled onto the muddy banks, there was one group experimenting with something new.
11:53Most fish fall into the family known as ray finned fish.
12:00But a few became fleshy finned.
12:06Why isn't well understood.
12:09It might have been that bigger plants, with the first stems and leaves, were starting to form thick banks of vegetation in the shallows.
12:20And it was easier for some fish to use their fins to pull them through the weeds as they prowled for prey.
12:27Their fins moved more to the sides and were supported by bone girdles to help them crawl along.
12:38These early species are only known from fossils, but might have been somewhat like scorpionfish and guernards,
12:48that spend most of their time on the sea floor and can use their strong fins to push themselves along.
12:55The End
12:56The End
12:57The End
12:58The End
12:59The End
13:00The End
13:01The End
13:02The End
13:03The End
13:04The End
13:05The End
13:06The End
13:07The End
13:08The End
13:27There was another ex-adaption already in place too.
13:30Lungs
13:35In most of the ray finned fish, the air pocket inside lost its function as a lung and became a swim bladder, a specialist buoyancy aid.
13:47But in these ancient creatures, it remained attached to the mouth and functioned as a primitive lung.
13:57There are a few fish today that retain that trait, like the aptly named lungfish.
14:07Modern lungfish still have strong, fleshy fins, and they have to surface and suck air into their lungs.
14:15Over time, the fleshy fins became more muscular and bones within them, firmer.
14:26The bones were anchored with a pelvic and pectoral girdle, so they supported the whole body.
14:35And the limbs rotated out to the sides, more like shoulders, to better support their weight.
14:42And they developed the first primitive joints.
14:49With the legs braced, these were the first creatures that could do push-ups.
14:56The fleshy fins would have moved in a diagonal, still based on the S-shaped movement of a swimming fish.
15:05They were the start of something new, the first tetrapods.
15:20Tetrapod means four feet.
15:24Anything that descended from these first pioneers are considered tetrapods.
15:29Even if their feet have subsequently been lost, as in snakes and dolphins.
15:44But this was a big step.
15:49All amphibians, reptiles, birds and mammals, including us, descended from these great granddaddies.
15:56Even today, we tetrapods are the new kids on the block.
16:06By the time these first walking fish came along, nine-tenths of the history of Earth had already passed.
16:16Of course, it took a while to move from here on in.
16:19About 80 million years of experimenting before they would be firmly established on land.
16:26To strengthen their waddles on the seabed, the fish's limbs became more attached to the backbone, giving more support.
16:43Especially once they were paddling in the shallows, where the strong framework supported them more easily against gravity.
16:49Most of the power in their walking came from the back limbs.
16:59The front were connected to the skull, but soon detached, giving more freedom to steer.
17:05This change also paved the way for a neck.
17:19Why they took the next step is a mystery.
17:21A long-held theory was that these walking fish were exploring shallow coastal lagoons, but that the pools could dry up during times of drought.
17:34So walking fish had the advantage of being able to take short strolls.
17:37Lungfish still operate in a similar way.
17:57Lungfish still operate in a similar way.
18:06They have even taken it a step further.
18:08When drought strikes and pools vanish,
18:20they can climb from the water,
18:33bending their bodies from side to side to side to allow their limbs to push them forwards.
18:46They can explore the banks, finding soft mud.
18:49They dig in, secrete a cocoon of slime,
18:58and can estivate, like hibernation,
19:01staying in torpor until rains come.
19:03Then they can dig themselves free and walk back to water.
19:21and walk back to water.
19:51This theory for the evolutionary driver is questioned,
20:06because the early legged fish didn't have adaptations to stop their bodies from drying out.
20:14It's possible that the fish would dash onto the land to get to places where predators couldn't follow,
20:19or to pursue their prey.
20:28A modern snakehead fish can use its long snake-like body to corral fish against the beach,
20:36and then rush them against the shallows.
20:38They are stuck and can be picked up.
20:47And the powerful fish can slither its way back into the water,
21:04breathing oxygen from the air with its gills.
21:07The eel catfish can actually target prey species on the land.
21:24It's modified gills can breathe the air.
21:43They are stuck and can be picked off.
21:47However, it has adaptations to feed.
21:55In the water, fish use a gulp technique for snatching prey.
22:01Just opening their mouth is enough to create a vacuum of water into the space, pulling the prey with it.
22:15This doesn't work on land, but the catfish has a modified spine,
22:19so it can raise the front of its body, but tilt its face downwards to pin its prey to the floor and consume it.
22:31The need to adapt to a world without suction feeding probably drove the evolution of the neck.
22:47It's a great place.
22:48It's a great place.
22:49It's a great place.
22:55Being able to get onto the land meant that the first tetrapods could enjoy the best of both worlds,
23:02moving above and below water, taking advantage of the food resources ashore that were out of the reach of other fish.
23:09Mud skippers demonstrate those benefits today.
23:39Beneath the waves, competition is fierce.
23:42Every niche is occupied.
23:49But in tidal habitats, there is a time frame.
23:57When the tide is high, fish and other creatures from the sea rush in to see what goodies have been washed in from the land.
24:09Time frame.
24:12It's noisy when line is oval in.
24:16It will move on through a tree radical onus Phanaku's widescreen continu.
24:19Thus, you'll see how it Mary is all swinging for the past.
24:21It is darker but from Brazil.
24:24Theinyl is open and joyful there.
24:26It is even more hollow than the European Oxapathors and 모습 that open us in the sky.
24:29It is the space walking on the ground.
24:31You can have東西 toibileq 사람이.
24:32But as the tide sinks, they must retreat.
24:54The exposed beach is beyond their reach.
25:02Mudskippers hide when the big ocean fish are around.
25:13It's a dangerous time.
25:18When dropping water levels chase them off, the coast is clear, literally.
25:33The mudskippers can have the beach to themselves.
25:36It's a rich and untapped resource of worms, crustaceans and algae.
25:48But to have this freedom, the mudskippers needed to find a way to temporarily cut their ties with water.
25:54Their main technical breakthrough is to breathe.
26:01They don't have lungs, but instead have enlarged cheek pouches over their gills.
26:08These hold bubbles of water like little portable oxygen tanks.
26:14Every now and then, a quick sip of the blue keeps them topped up.
26:29Like modern frogs, they can breathe through their skin and the skin of their throats,
26:34thanks to the thin membranes and rich network of capillaries beneath.
26:42But to allow gas exchange, the membranes must be wet, so the skippers need an occasional dip.
26:49But are then wet and ready to forage over the beach until the tide returns.
27:03They can move by coiling their bodies in an S-shape and flicking their tails to hop.
27:10But they also have strong front flippers.
27:14The jointed elbows are not the same as the early walkers.
27:17These are raid fish, but provide a modern analogy as they walk up the beach.
27:23Both flippers moving together in a motion called crutching,
27:27as it resembles a person hopping along on crutches.
27:31Their eyes have moved to the top of their heads,
27:45and are remarkably frog-like to give them 360-degree vision to look for danger.
27:51Truly amphibious, they are happier on land than in water.
28:05And perhaps this is why the first fish came ashore,
28:08to exploit a niche that was beyond the reach of others.
28:12The more those early fish were out of the water,
28:21the stronger and more supported their skeletons became.
28:29They became more recognisable as land animals.
28:33As they cut the ties with their marine lives, the amphibians were born.
28:47It's hard to imagine a greater change.
28:53Going from a liquid environment,
28:55one where oxygen is only available dissolved in water as part of H2O,
28:59and where the water supports objects, easing the forces of gravity.
29:20Of course, the process was not linear.
29:25Many fossils show animals at different times,
29:27trying different ways of using new habitats.
29:36The animals were not on a predetermined evolutionary pathway,
29:40but instead were adapting features that made them better at doing what they did.
29:49Sometimes these secondarily presented them with new opportunities.
29:57several groups experimented with forays onto land.
30:01And which of these started the trend that was to become amphibians is not clear.
30:09Like their ancient ancestors,
30:12some modern amphibians remain mostly tied to the water.
30:15The family known as the giant salamanders evolved under the feet of dinosaurs,
30:28and they haven't changed at all since that time.
30:31Though their lifestyles are somewhat similar to the much more ancient early amphibians.
30:45They have lungs, so can breathe air, but they have another trait they share with all amphibians.
30:59They can breathe through their skin.
31:02In the different kinds of giant salamanders that spend almost all of their time in the water.
31:11Their skin looks like they bought a onesie that was several times too big for them.
31:16But the saggy, wrinkled skin increases their surface area.
31:19More skin exposed to the water to maximize their oxygen intake.
31:29They have deep, muscular tails.
31:35And move with the same winding S-shape as their fishy ancestors.
31:40From roughly 360 million years ago, through the Carboniferous and Permian periods,
32:03amphibians were the dominant animals.
32:10Some got pretty large.
32:13The biggest known was nine meters long.
32:16Much bigger than a great white shark or saltwater crocodile.
32:27Giant salamanders, which are occasionally two meters long,
32:31are the last remnant of that supersized past.
32:33They have one feature that's different from the earliest amphibians.
32:41Their eyes.
32:43Modern giant salamanders have tiny eyes and poor vision.
32:48But there is evidence that as those fleshy-finned walking fish prowling the shallows adapted to their environment,
32:57their eyes were getting bigger.
32:59Some theories suggest that the pattern in the fossil record show that eyes were becoming larger and moving towards the top of the head.
33:14Perhaps because they were hunting animals above the surface, lying in wait as crocodiles do today.
33:19It gave them the chance to eye with envy the growing riches on the land.
33:29Underwater, visibility is very limited.
33:45So primitive species had quite simple vision.
33:48And they needed to adapt their behavior to short-range stimuli.
33:55To flee or pounce as either predators or prey came close enough to discern.
34:01It had to be all about rapid response.
34:06It has been suggested that using eyes above water in a much clearer medium where long vision is possible,
34:23drove better eyesight and that this in turn might have improved cognition and complex planning.
34:29The animals didn't need to be so reactive.
34:34They could spot opportunities and plan their approach.
34:39They could spot opportunities and plan their approach.
34:40They could spot opportunities and plan their approach.
35:09could this have been a driver for more complex cognition?
35:16This improved eyesight might have been a feature that made a transition to the land easier.
35:25The size and placement of eyes in most modern amphibians is little changed.
35:48Another hurdle they had to overcome was to have more efficient lungs.
35:53Air-breathing fish, like lungfish, gulp air and tilt their bodies to help it move into their lungs, using its natural buoyancy.
36:09But during the transition from fish to amphibians, it was replaced with a muscle-driven process, the buccal pump.
36:17Most modern amphibians share the same technique, to breathe through their nostrils and using their throats like bellows to push the air into their lungs.
36:32At the same time as the throat raises, it pushes the old air out of the lungs, which can be expelled.
36:46Their nostrils become more complex, moving from single external nostrils in fish that simply monitored the water passing through them to paired nostrils.
36:55The external ones leading to internal ones and linking them to the throat, helping to advance their ability to sample scent particles from the air.
37:09These eager earth-walkers, as they moved further from the water, also improved their feeding apparatus, developing a more powerful tongue to manipulate food that wasn't drifting in water.
37:27They also needed to sort out their wardrobes.
37:44By having more keratin in their skin to make it stronger, it helped to protect against abrasion from contact with the land.
37:55It remains very thin and permeable, so they can absorb oxygen through it.
38:02But to do that, they needed to stay moist.
38:06For these creatures, one of the biggest challenges of life on land was to prevent desiccation.
38:15They overcame this problem by developing mucus glands that can secrete slime, a slippery layer that helps trap the moisture in.
38:27With these breakthrough innovations, they were ready to conquer the land.
38:33The world they inherited was a land of riches.
38:45Amphibians rose to fame during the Carboniferous, which means coal-bearing.
38:52It was the age of coal because trees had appeared on the scene.
38:57Plant life proliferated.
39:03And it was their remains that were to become the bulk of the fossil fuel we utilize today.
39:09Beneath the trees were giant ferns, mosses and horsetails.
39:23The plant explosion radically changed the Earth's atmosphere.
39:28They were pumping out oxygen, the gas of life.
39:32At its peak in the Carboniferous, oxygen levels made up 35% of the air.
39:45Today, it's only 21%.
39:47It may have been this extra oxygen that gave invertebrates a boost.
39:53Giant cockroaches and scorpions scurried around the ferns.
40:00Centipedes were as big as humans.
40:13And it's when the first insects took to the air,
40:16enjoying greater energy levels thanks to all the O2.
40:26There were dragonflies the size of hawks.
40:30It was a feast for the amphibians.
40:40And without competition from other large animals, they flourished.
40:47But they did have one Achilles heel.
41:00They were still tied to the water.
41:06Almost all amphibians, regardless of how terrestrial they are in their lifestyle, must return to the water to breed.
41:13How they get together to fertilize the eggs varies from species to species.
41:31Most salamanders, like these newts, fertilize their eggs internally.
41:48The male deposits a sperm packet that the female will take into her body.
41:58Frogs, on the other hand, get together in a scrum.
42:13Frogs, on the other hand, get together in a scrum.
42:15And as the female releases her eggs, the male releases sperm and fertilization happens outside of the body.
42:27But crucially, however it starts, the eggs are blobs of jelly.
42:42They are permeable, which means that water can flow in and out.
42:55If they are not in liquid, they will dry out, killing off the embryos.
43:01So no matter how advanced they got at moving on land, most amphibians are still bound to the water.
43:14Amphibians are also pretty unique because they have two life stages.
43:20Their larvae, often known as tadpoles, are fully aquatic, like their ancestors, and still have gills.
43:34They have to stay entirely in the water until they have grown enough to go through a metamorphosis,
43:43absorbing their gills and switching to lungs, and gradually growing limbs.
43:56Only with the transformation complete can they make their way onto land.
44:04This egg challenge was the final hurdle that our own ancestors had to overcome
44:16before we could fully cut our ties with water.
44:26The amphibian tie to water made them vulnerable to droughts.
44:30And as the Carboniferous progressed, the climate was warming.
44:37The Earth was moving, forming one giant landmass.
44:42But amphibians had to stay close to the coast or bodies of water.
44:50Not all of them did.
44:52Some pushed for world domination, finding ways to live drier lives.
45:01Somewhere between 320 and 310 million years ago,
45:07a new group of animals emerged from the slimy ancestors.
45:19Unlike the permeable skins of amphibians,
45:21they developed scaly skin that prevented them from drying out.
45:25But more importantly, they found a way to surround their eggs with thick, leathery shells.
45:42It was a mineralization of the outside of the egg that built the first protective layer.
45:53Though there were several other layers inside.
45:59Most crucially, the amnion, a sack of liquid surrounding the embryo,
46:05a protected birthing pool in which a baby can grow.
46:15They have a large yolk to nourish the embryo.
46:22With this well-fed and protected development,
46:25this new form of life, the amniote, cut out the need for a larval form.
46:30The babies have egg teeth, small sharp scales on their noses to cut their way free of the shell.
46:43And emerge as perfect replicas of their parents.
46:52And this is a long timeout.
46:53This is an amazing animal.
46:54And interesting things to be found in the air.
46:56The animals I하기 for were very long.
46:58They are so mature people.
47:00They are new animals.
47:02They are new animals.
47:04They have lost to them.
47:05They have seen on the air-man participants.
47:07That is a very new animal.
47:09And they are new animals.
47:10And the animals I front over the world.
47:13And we see their animals.
47:15They have wild animals.
47:17And the animals have a wonderful animal.
47:18And the animals have seen animals,
47:19The amniotes had advanced the abilities of tetrapods.
47:27With ties to water cut, they could rule the world.
47:42The amniotes were to further divide.
47:45Split into two main groups based on the number of holes in their skulls.
47:55The synapsids were pretty important to us.
48:02They were to give rise to the mammals.
48:06Their evolution was another step towards humankind.
48:15The other group, the diapsids, were destined for even greater things.
48:20In the next chapter of life on Earth.
48:21The other group, the diapsids, were destined for even greater things.
48:27In the next chapter of life on Earth.
48:30The next chapter of life on Earth.
48:31The next chapter of life on Earth.
48:32The next chapter of life on Earth.
48:33The next chapter of life on Earth.
48:34The next chapter of life on Earth.
48:35The next chapter of life on Earth.
48:36The next chapter of life on Earth.
48:37The next chapter of life on Earth.
48:38The next chapter of life on Earth.
48:39The next chapter of life on Earth.
48:40The next chapter of life on Earth.
48:41The next chapter of life on Earth.
48:42The next chapter of life on Earth.
48:43The next chapter of life on Earth.
48:44The next chapter of life on Earth.
48:45The next chapter of life on Earth.
48:46The next chapter of life on Earth.
48:47The next chapter of life on Earth.
48:48The next chapter of life on Earth.