- 5 weeks ago
Ancient Australian fossil sites provide crucial clues about how prehistoric creatures made the monumental shift from water to land, also highlights the biological leaps required for land dominance, including the development of legs, lungs, and the search for shelter and sunlight...
因为地球生命从无到有,从简单到复杂;从无脊椎到有脊椎,从水生到陆生;芸芸众生、林林总总,经历了约40亿年的漫长演变历程.地球上最早的、确切的生命印记是发现于澳大利亚西部34.5亿年前的岩石中的微生物群落化石。
因为地球生命从无到有,从简单到复杂;从无脊椎到有脊椎,从水生到陆生;芸芸众生、林林总总,经历了约40亿年的漫长演变历程.地球上最早的、确切的生命印记是发现于澳大利亚西部34.5亿年前的岩石中的微生物群落化石。
Category
📚
LearningTranscript
00:00Over four billion years in the making.
00:06An island adrift in southern seas.
00:10It's Australia.
00:12The giant down under.
00:16A young nation.
00:19With all the gifts of the modern age.
00:22That move beyond the cities.
00:26And an ancient land awaits.
00:30One nearly as old as the earth itself.
00:39Australia is a puzzle.
00:42Put together in prehistoric times.
00:47And the clues that unlock the mystery
00:49can be found scattered across Australia's sunburnt face.
01:00I'm Richard Smith.
01:02And this is an amazing country.
01:07I'll show you that every rock has a history.
01:11Every creature.
01:12A tale of survival against the odds.
01:16Join me on an epic journey across a mighty continent.
01:22And far back in time.
01:25Of all continents on earth,
01:28none preserve the great saga of our planet
01:30and the evolution of life quite like this one.
01:34Nowhere else can you so simply jump in a car
01:38and travel back to the dawn of time.
01:42In this episode.
01:44The world above water has sat silent and lifeless.
01:50But now armies storm the beaches.
01:53And biology conquers the world.
01:55It's the battle for life on earth.
01:59The struggle for legs and lungs.
02:03Sunlight and shelter.
02:05Even the quest for sex.
02:08From Australia's ancient stones
02:10comes the story of our world.
02:15Australia's first four billion years.
02:19Life explodes.
02:22Right now on NOVA.
02:39Major funding for NOVA is provided by the following.
02:45The David H. Koch Fund for Science.
02:48Supporting NOVA and promoting public understanding of science.
02:55And by the Corporation for Public Broadcasting.
03:00And by contributions to your PBS station from viewers like you.
03:24If Australia seems a little tired and worn,
03:27it's because she's seen a lot happen over the course of her long life.
03:42In the last episode,
03:44our journey down the road of time
03:46began with the Earth's fiery birth.
03:49Four and a half billion years ago.
03:54We passed the first fumbles of life
03:57in the waters skirting Australia's ancient shoreline.
04:04Along the way,
04:05we've seen the planet change from poisonous to pleasant.
04:10And the first animals begin to swim the seas.
04:17Yet, save for a thin smear of slime and bacteria
04:20along the soggiest of margins,
04:24all the continents themselves had lain bare for over four billion years.
04:32In terms of the lifetime of a continent,
04:35Australia and the world around it is still an infant,
04:39still attached to its motherland,
04:41the great supercontinent Gondwana,
04:44and still a blank canvas on land.
04:48Your destination is the Paleozoic.
04:52Now, with 90% of Earth history behind us,
04:56it's time for conquest.
05:13The tremendous explosion of life that began in the oceans of the Cambrian
05:17was still going strong at the dawn of the Ordovician,
05:19the second of the six great periods that make up the Paleozoic.
05:24And it was in Ordovician oceans
05:26that a second wave of animal experimentation began as well.
05:30One that ultimately would lead to the first Australians coming ashore.
05:37With the seas now crowded with life,
05:39the first tentative footsteps onto land were not far away.
05:48Now, at the time,
05:49Australia was just one of an exotic collection of lands,
05:52including India, Africa, South America and Antarctica,
05:56that today we call the supercontinent Gondwana.
06:01Australia's position was just about here.
06:03Right at the tip,
06:06just north of the equator,
06:07and mostly underwater.
06:14Oceans were rising around the planet,
06:17and seawater flooded in across parts of Central Australia.
06:24At the time,
06:26the sea of sand we know today as the Simpson Desert
06:29was slap-bang in the middle of the Larrapinta Seaway.
06:33A tongue of warm ocean water that licked right across the country.
06:41Back then, this bouncy drive would have been a bumpy boat crossing.
06:51As the rising waters swept in, they carried a rich bloom of plankton.
06:57Food for some of the earliest fish to swim in the sea.
07:03And they swam right here, right above me.
07:11The last vestiges of the old Larrapinta sea floor
07:15lie tumbling from the top of the mesa-shaped hills of the Simpson Desert.
07:21Even in the best of seasons like this,
07:24the Simpson is a harsh, unforgiving landscape.
07:30Now, you probably wouldn't expect to find the world's earliest fish
07:34in the dead centre of the driest inhabited continent on the planet today.
07:39But it was on the side of this hill in the Simpson Desert
07:42where the fossil of Arendaspis lay waiting to be discovered.
07:50We only know Arendaspis from the bony headplates and body scales it left behind.
07:57Enough to tell that this was a fish with a simple tail and no real fins.
08:03Nor did fish like Arendaspis have jaws or even teeth.
08:08They probably just slurped in whatever morsels they could find.
08:17But don't underestimate the significance of this fish.
08:22This was an animal with a backbone.
08:25It's one of the first vertebrates,
08:27so we can all trace our ancestry back to an animal like this.
08:37But giant invertebrates ruled these Ordovician seas.
08:41And to them, Arendaspis was just a bite-sized snack.
08:50While the first fish took to swimming out of danger,
08:53their invertebrate foes would soon be flexing their leg muscles
08:58in a different way.
09:00Time to put the foot down
09:02and head for the seaside in the Silurian.
09:16On a remote stretch of the Western Australian coast,
09:19the 21st century Indian Ocean eats away at an ancient Silurian shoreline.
09:28Wind and water have exposed the burrows of long-gone animals
09:32in the sandy coastal cliffs.
09:37The original inhabitants of the burrows remain a mystery.
09:40But not the predators attracted by such rich pickings
09:44along the prehistoric shoreline.
09:51Clues to their identity are revealed in the rocks
09:55of nearby Murchison Gorge.
09:58Here, the river has sliced deep into the Silurian past.
10:05The Murchison Gorge back in the Silurian
10:08wasn't a gorge at all, of course.
10:10It was a vast estuarine floodplain
10:13with rivers winding down from the hills in the distance,
10:16carrying sand into the sea.
10:18But for the first time in the history of the planet,
10:21those Silurian shorelines down there were alive with animal activity.
10:32This may not have been a good time to take the kids to the beach.
10:38Armies of sea scorpions were massing in the shallows.
10:43Known to palaeontologists as Eurypterids,
10:47some of these intimidating arthropods grew as long as a man is tall,
10:52and they bristled with armoured legs and fearsome claws.
10:59Far less threatening was this bloke.
11:03Calbaria was probably an ancestor of modern crustaceans
11:07and grew about as long as a king prawn.
11:11Whether in search of food, a safe place to mate,
11:15or simply to avoid the nasty neighbours,
11:18Calbaria clambered ashore.
11:24And left clear imprints of its many tiny feet in the rocks.
11:34A descent into Murchison Gorge
11:37takes you back to those ancient Silurian shorelines.
11:43Down here, it soon becomes clear
11:46that the sea scorpions followed Calbaria ashore.
11:52This is what we call Track Central.
11:55I can see why.
11:56There are tracks everywhere.
11:58This is probably the best site in the park
11:59to look at these Eurypterid tracks.
12:02Our animals come through here.
12:03So in shallow water?
12:04Shallow water.
12:05OK, it's been slipping and sliding a little bit
12:07as it comes around the corner.
12:08That's exactly right.
12:09But here, I mean, I can see clearly
12:11this is kind of sloppy-looking track here.
12:13Yep, it is.
12:14But once you come over here,
12:15you start seeing really discreet footprints.
12:18Clear, graphic demonstration of a creature
12:21walking out of the water and onto dry land.
12:24And where we are here in the depth of the gorge,
12:27we're in the oldest of the Silurian sediments in this area.
12:30Quite a historic little spot you've got here.
12:32Very, very.
12:35These trackways offer some of the oldest evidence
12:38for animals on land.
12:41And even though these formidable beasts
12:44could not stray far from the water's edge,
12:46a beachhead had been established.
12:52So this seems to be how the animal invasion of the land began,
12:57with a scary assortment of arthropods with attitude
13:01slinking and scuttling ashore
13:02onto the wet sands of a new frontier.
13:07But this wasn't just a continent to exploit.
13:10There was a whole planet for the taking.
13:18Waiting beyond the breakers
13:20were all the wide brown lands of Earth.
13:30Australia, already under animal assault,
13:34found itself centre stage
13:36for the waves of invasion and conquest that would follow.
13:44But animals were not going to get far inland
13:48without help from plants.
13:55They, too, came out of the sea.
13:58First as slime,
14:00then as low-spreading things that clung to dampness.
14:06Seaweeds captured the shoreline.
14:08Then tiny forests of lichens, liverworts and mosses
14:13pioneered the moving land.
14:25Today, we take for granted the plants around us.
14:29It's their oxygen we breathe.
14:31Their food we eat.
14:34But the land can be a tough, dry place to live.
14:38And any plant going to make it big out here
14:41needed a thick skin
14:43and a little internal fortitude.
14:47Just such a plant first took root somewhere around here.
15:05If you thought that this was just another ordinary roadside cutting,
15:09on a pretty but ordinary country road,
15:12well, of course, you'd be dead wrong.
15:13It was here near Yeay in Victoria
15:16that fossils of some of the world's earliest land plants were found.
15:21Indeed, these rocks contain the first signs
15:25of the greening of Gondwana.
15:29Just amazing.
15:34This is Barra-Gwenathia.
15:37Possibly the oldest true land plant in the world.
15:41Not much to look at, perhaps.
15:43But with green leaves and a stem to carry sap internally
15:47and to support its weight,
15:49the world above water was its oyster.
15:54In life, it would have looked much like this.
15:58This is a lycopod, or club moss, as was Barra-Gwenathia,
16:02rising out of the water in a coastal bog in Queensland today.
16:11These are the direct descendants of the green revolutionaries
16:15who changed the face of the planet.
16:20If you look closely,
16:22you can see many of these Silurian-type plants
16:25still clinging on in damp corners around the country.
16:28Here's a rainforest Selaginella,
16:32a tropical tassel fern,
16:35a club moss in Tasmania,
16:38even a Silotum in Sydney.
16:46Plant life had by now engineered a solution
16:49to the ultraviolet radiation
16:51that had been sterilising the Earth's surface.
16:55An ozone layer, built from excess oxygen.
17:03The low spreading thickets provided the perfect humid cover
17:08for other arthropod forms like millipedes, centipedes and mites
17:12to make the transition to the land complete.
17:17Some mollusks even brought their own homes
17:21because it was still not a very welcoming place.
17:31While life was exploring the fringes,
17:34most of the Gondwanan supercontinent was dry,
17:38probably still quite bare,
17:41and almost certainly windy.
17:46The Larapinta Seaway had receded,
17:49leaving much of what is now central Australia
17:52resembling the Sahara Desert.
17:58And that desert became mountains.
18:21Titanic tectonic forces, operating over a span of 150 million years,
18:27buckled the Earth and pushed great folds of rock into the air.
18:39In their heyday,
18:41Central Australia's McDonnell Ranges
18:44would have been a mountaineer's dream,
18:47as high it's thought as any on Earth today.
18:53But Australia would never experience mountain building on this scale again.
19:19After a near eternity of erosion,
19:22the diminished remnants of the McDonnell Ranges
19:26still run in long jagged wrinkles
19:30across the heart of Australia.
19:44From the air, they protrude into this ancient landscape,
19:49like the bony skeleton over which the dry skin of a tired continent is draped.
20:11All other continents boast mighty mountain ranges.
20:16The Rockies, the Alps, the Andes, the Himalayas.
20:20But they're all relative newcomers,
20:24and mostly still growing.
20:32What sets Australia's landscape apart is its venerable antiquity,
20:38and its great flatness.
20:45Australia is actually quite remarkably flat.
20:48And when you look at it from space,
20:52it's not just flat, but it's apparently saucer-shaped.
20:58It's a saucer that holds many secrets for geologist Lisa Worrell.
21:04Her interest is not so much the bedrock of the outback,
21:07but the story of all its eroded remnants,
21:11accumulated over a vast gulf of time.
21:15We know parts of Australia have been exposed for millions,
21:20if not billions of years.
21:28We're part way through an ongoing geological story.
21:34The rivers that in Australia mostly drain inland
21:38are actually losing or have lost the ability
21:42to carry sediments out and down into the seas.
21:45So inland Australia is filling up with sediments.
21:58Outback Australia is drowning in sand.
22:05Head towards the coast in any direction from the red centre,
22:08and you cross oceans of these old, weathered sediments.
22:14It's the sort of landscape you should expect
22:17from the flattest continent on the globe.
22:23Travelling north-west, it's 700 miles
22:26before you reach the next significant patch of high rocky ground.
22:33The Kimberley.
22:40While mountains were still pushing skywards in the continent's heart,
22:45up here in Pernalulu National Park,
22:47others were already wearing down to nothing.
23:03CHOIR SINGS
23:08Epic tales of erosion and recycling lie behind most geological features
23:14in the Australian landscape.
23:21The sands and gravels that made the Bungle Bungle Ranges
23:25started arriving here about 375 million years ago.
23:30Dumped by rivers that wore away highlands far older and now long gone.
23:41This landscape was already second-hand, long before the rocks began eroding away
23:47into the famous striped beehive domes we see today.
23:56The distinctive striping of the rocks here is a dead giveaway to how the Bungle Bungles were formed,
24:02layer by layer, as mighty rivers wash sediment from distant mountain ranges to fill the basin.
24:13This unfolding landscape is a two-tone testament to change.
24:19Left as a parting gift by rivers that ran down into a Devonian tropical sea.
24:40300 dusty miles to the west of the Bungle Bungles,
24:43and you can run down to that same ancient sea.
24:48Once home to some of the most spectacular tropical reefs on the planet.
24:58Surprisingly, you can still visit these reefs today.
25:11I'm standing at the base of the Great Devonian Barrier Reef.
25:17These towering limestone cliffs were once towers of life
25:21rising into the clear sunlit waters of a colossal reef system that once circled the Kimberley.
25:32In both size and significance,
25:35the Devonian Reef rivalled modern Australia's Great Barrier Reef.
25:41Its limestone ramparts were once festooned with crinoids and corals, sponges and sea squirts,
25:48and many other creatures still found clinging on in tropical waters.
25:55That Devonian life is gone, but the Great Reef walls still stand to this day.
26:06It's easier to see from the air.
26:12In the same way that the Great Barrier Reef fringes the Queensland coast today,
26:18the Great Devonian Reef skirted in a sweeping curve around the Kimberley hinterland
26:22for perhaps 600 miles.
26:30Reef after reef line up across the landscape as if a giant bath plug had been pulled.
26:47The Great Barrier Reef
26:48At Tunnel Creek, one such stream has carved its way right through the Devonian Limestone Range.
26:59It's a deliciously cool change from the sweltering heat outside
27:04and offers dark access to the very heart of the reef itself.
27:18A whole suite of reef building organisms built this Great Devonian Reef above me.
27:23You can see a lot of their ghostly remains in the rock still.
27:27Sponges, stromatolites, corals, strange extinct things called stromatoporoids.
27:34But the real stars of the show here weren't the things that made the reef,
27:39but the things that swam around outside it.
27:41Things with fins.
27:43Because this was the great age of the fishes.
27:53It was in the Devonian that for the first time, fish filled the oceans.
28:00Fish of all shapes and sizes.
28:04Just not quite the shapes and sizes we see today.
28:17Like the reefs themselves, the fish of the Devonian Northwest are amazingly well preserved.
28:26Protected in limestone nodules scattered across nearby Gogo Station.
28:31Ow!
28:35You don't get a lot of bites around here.
28:38About one nodule in every thousand yields a good fossil strike.
28:47But whenever you catch a Gogo fish, it's always something special.
28:55Oh wow!
28:56That's a lot of bone.
28:58That's all bone there.
28:59That's some very large plates.
29:02So what do you think that is, Gavin?
29:05It's clearly a large placoderm.
29:09Probably a big arthrodite.
29:10That's why.
29:20Kings of the Devonian Seas were the placoderms.
29:27Fish had moved on since the days of Arendaspis.
29:31Now they had jaws, fins and teeth to go with their bony headplates.
29:39The front part of the body was covered in these bony plates.
29:45And then the tail would be pretty much shark-like.
29:50They were in fact very agile, successful predators.
29:55They had a highly developed sensory system.
29:58Some of them had electrosensory perception, like modern sharks and rays.
30:04Many of these fossil features have been preserved in fabulous 3D.
30:10Oh look, there's some ridging.
30:12The Gogo nodules have protected the fossils from being crushed.
30:16Do you think it might be a holonema?
30:18A nice bath and acid's going to clear it up.
30:21Soak it in some water and scrub it with it.
30:23Toothbrush, it'll be much water.
30:24I don't know, if I'm not getting a shower at night, this fish certainly isn't.
30:35It's only once the limestone nodule is dissolved away in acid in the lab that the fossilised fish within come
30:42back to life.
30:45In astonishing detail.
30:52Scales, teeth, eye sockets, brain cases, bones and fin rays.
30:58The fish are all so fabulously well preserved for their age that even soft body bits can be made out.
31:06In more ways than one, these are pretty sexy fossils.
31:13Well this one here is particularly interesting because it's one of the few male fossils that we have.
31:19And we can tell that because it has this clasper.
31:22What, like in a shark?
31:23Very much like a shark.
31:25This bony tube structure is the oldest confirmed male appendage.
31:31A fishy private part for impregnating a female.
31:40The Devonian was an important time for vertebrate life.
31:44With many biological experiments underway.
31:48Including the all-important vertebrate sex.
31:57Even today, sex in the sea can be a bit of a hit or miss affair.
32:03A trade-off between precision and plenty.
32:09Without coupling and live birth, vulnerable progeny sink or swim on their own.
32:18Not a strategy destined for success on land.
32:28This is a portrait of the world's oldest preserved mother with child.
32:34And we have the fossil to prove it.
32:38And this is perhaps our most famous discovery to date.
32:42This is the mother fish.
32:43And this is the real kind of clincher we had that you could have live birth.
32:48And it's this little structure here right around the bottom.
32:52And that is the umbilical cord which is attaching the mother to her unborn embryo.
33:00My goodness, that's the world's earliest umbilical cord we know of.
33:05That is, it's the world's earliest evidence of live birth in any vertebrate.
33:12Our backbone ancestors were making all the right moves.
33:18Already on the road to becoming social, smart and sexy.
33:25And they were everywhere.
33:31As rain fell on Australia's newly constructed east, rivers ran back down towards the sea.
33:38Filling the freshwater lakes and backwaters of the new coastal landscape.
33:46Throw a line into one of those Devonian rivers and you would have caught plenty of fish that looked almost
33:52identical to this.
33:58Whoa, hi big guy.
34:01Oh, look at you.
34:02Aren't you something special?
34:04Now this is something truly special.
34:07A living link to our fossil past.
34:09It's the Queensland lungfish, Neotheratidus fosteri.
34:13And I'm trying to hold him my hope.
34:16Now, he is the most primitive of the handful of lungfish that still swim on planet Earth.
34:22Think about it for a moment.
34:25These guys were already ancient history, a hundred million years before the first dinosaurs walked the Earth.
34:32And if you're worried about that fish out of water thing,
34:36these guys are called lungfish for a reason.
34:39They're built for it.
34:41There you go matey, off you go.
34:55When lungfish moved from the sea into fresh water in the Devonian, they brought with them the ability to breathe
35:01with or without gills, when the going got tough.
35:08It's a skill that still stands these remarkable living fossils in good stead.
35:14They live on in just a few river systems in South East Queensland.
35:19And when oxygen levels fall, they can switch to gulping air from the surface.
35:27It's a strategy that has doubtless allowed them to struggle through more than one Australian drought.
35:35Not all fish have been so lucky.
35:45As far as we can tell, drought is a problem that has plagued the country for at least 360 million
35:52years.
35:55We know this because in 1955, the local council sent a bulldozer to smooth out a bad bend on the
36:03Canoundra to Goolagong Road.
36:18Well, the bad bend in the Canoundra to Goolagong Road is still here.
36:22And you wouldn't know it to look at it, but I've just parked right on top of one of the
36:27most spectacular Devonian freshwater fish sites in the world.
36:32The roadworks inadvertently lifted the lid on Australia's oldest known outback waterhole.
36:43When a paleontological team returned to open the site,
36:46thousands of fish tumbled out.
36:52They were lying on the slabs just as they had been the day they all died together when their waterhole
36:59dried up.
37:03Like their saltwater go-go cousins, many were armour-plated placoderms.
37:16There were lungfish here as well.
37:19And another related group of fishes with four-lobed fins that we humans should be very thankful for.
37:33Of the 4,000 or more fish uncovered on these Canoundra slabs, this one is special.
37:41It's been given the name Canoundra grossi, after the town of course, but its real claim to fame are the
37:48features that it shares with those fish-like animals that were leaving the water behind.
37:55A single pair of external nostrils suggests it too could breathe with both lungs and gills.
38:04And it was one of the lobed-finned fish.
38:06A group with four rim-like fins, with a bony internal structure we can recognise in our own arms and
38:14legs.
38:20It's not hard to imagine that somewhere in the drying Devonian waterhole at Canoundra, at least one of those fish
38:28might have got away.
38:31By walking onto land.
38:35And this is why.
38:38Hard evidence in the form of fossilised four-legged footprints, of about the same age, and found near the Genoa
38:46River in Victoria.
38:56It was a different Genoa River, but these early fish-like tetrapods, about three feet long, were among the first
39:04animals on Earth to feel the sand between their toes.
39:12It's not hard to see how the evolution of walking limbs might have come about.
39:20Many Australian fish species today are still testing out ways of getting about without swimming.
39:28This is the aptly named handfish.
39:32Hopping and skipping its way along the Derwent Estuary in Tasmania.
39:40And this, that master of the tropical mangrove, the mudskipper.
39:48However they'd managed it in the first place, amphibians soon walked out into the botanical wonderland of the Carboniferous.
40:10The Carboniferous saw all sorts of new plants putting down roots and pumping out oxygen at levels the planet had
40:18never seen before.
40:24Huge forests, especially in the Northern Hemisphere, helped push up oxygen levels in the atmosphere, perhaps 50% higher than
40:33today.
40:37The extra oxygen saw some invertebrates grow to enormous sizes.
40:43It allowed millipedes the size of snakes to scuttle across the land, and insects as large as seagulls to take
40:52to the air.
40:56The rich insect pickings on offer must have favoured the spread of the amphibians now moving through the landscape.
41:06But like their froggy descendants today, these ancestral four-legged animals needed to return to water to reproduce.
41:19Some time in the Carboniferous, the first reptiles overcame this limitation.
41:26Wrapping their eggs in a membrane blanket with a hard outer shell, reptiles could take a watery egg with them
41:33on their travels.
41:37It was a solution so successful that it allowed the many contemporary lizards of Oz to still claim the arid
41:46Australian outback as their own.
41:56There was yet another Carboniferous legacy left out here.
42:04The greening of the earth began to at least partly turn Australia red.
42:12The highly oxygenated atmosphere began to rust the iron-rich soils and rocks of the outback.
42:22And some rocks out here are bigger than others.
42:30It's very impressive.
42:32It's a fabulous monolith, isn't it?
42:34It's justly famous for being the largest bit of rock, lump of rock in the world.
42:40Yeah. And it's just gorgeous.
42:43And it's very red.
42:46The colour of weathered iron minerals like haematite.
42:52Many of the rocks of Australia are rusted.
42:56We know that we had oxidising rocks back to around the Permocarboniferous.
43:01That colouration of the landscape is in fact very old and very persistent.
43:12But at the end of the Carboniferous, just as world domination lay within the reptiles' grasp,
43:20the changing world threw up another great climate challenge.
43:31The drift of Gondwana saw Australia heading south and getting colder.
43:39It was more than just the location.
43:43The earth had slipped into another ice age.
43:47And Australia was covered in more ice than it would ever see again.
44:00By the time we reached the Permian, a deep chill had settled in.
44:06Ice carved its calling card on the country.
44:11Nowhere more clearly than the Floro Peninsula in South Australia.
44:22The bedrock here was scoured by glaciers.
44:28All these long scratches and grooves in this smooth surface were gouged by rocks and debris
44:33being dragged along at the bottom of an ice sheet flowing in this direction.
44:41What these rocks are telling us is that clearly if you look to the south of Australia back in the
44:46Permian,
44:47you wouldn't have seen the open ocean we see today.
44:50If you look back that way, you would have seen the mountains of Antarctica.
45:18It's incredible to think that if you travelled to Australia in the early Permian,
45:22the landscape probably looked much like this over at least the southern half of the continent.
45:29Evidence for ice can be found stretching across the country,
45:33from the Kimberley to the coast of Tasmania.
45:42But this cold landscape was not frozen solid like Antarctica.
45:50It was seasonally cold, more like a northern Alaska or Canada.
46:00Well, Permian Australia might have been freezing cold, but it was far from lifeless.
46:07These remarkable rocks on Moriah Island are just stuffed to the gunwales with shellfish.
46:13And nearly every one of the animals in the rocks here, and in the rocks behind me, and the cliffs
46:19in the distance,
46:20belong to one species of clam.
46:23This one, called Urodesma.
46:33What Australia's Permian Ocean lacked in diversity, it made up for with abundance.
46:44Life crowded the sea floor.
46:57It was the same story on land.
47:00And the proof can be found hidden underneath Australia's moist eastern seaboard.
47:07Much of it right under modern Sydney.
47:14Beneath the eucalypt forests that surround the city of Sydney today
47:18lie cool climate forests far more ancient.
47:22Welcome underground, gentlemen.
47:23Ground floor of the Permian.
47:29I'm heading half a mile down into a coal mine at Hellensburg on Sydney's southern outskirts.
47:40The seams of rich black coal here have been mined for longer than any other in the country.
47:50What you're looking at here is the exhumation.
47:53Half a kilometre underground of the dead black graveyard of a vast swampy forest that once stretched right across the
48:01Sydney basin.
48:02It's hard, messy, noisy work.
48:05But there's treasure in this coal.
48:07The raw energy of fossilised sunlight.
48:16Half the energy used to light Australian homes, fuel industry, cool beer and power this program comes from Permian plants
48:27buried faster than they decomposed over a quarter of a billion years ago.
48:42When scientists looked closely at these coal scenes, they found something not seen in the Australian forest growing so far
48:48above me today.
48:49The fossil leaves they encountered were found in alternating repeated layers.
48:56Every autumn it seems, these now blackened Permian coal forests were once a riot of colour.
49:10One tree above all others dominated the Permian forests.
49:16Glossopterus.
49:22Glossopterus had solved another part of the problem of reproducing on dry land by encasing its embryo in a protective
49:31seedy shell.
49:34So successfully, it turns out, that fossilised Glossopterus leaves are the botanical signature of all Gondwannon lands.
49:47The planet had come of age in the Permian.
49:53Here was a world with great oxygen producing forests, inhabited by animals with four legs.
50:01Insects had taken to the skies and the seas were brimming with animals.
50:09Life on Earth was going swimmingly well.
50:16And then, suddenly, everything went diabolically wrong.
50:30Well, the Permian came to a sudden and very sticky end, right here, at the greatest extinction boundary in the
50:38planet's history.
50:39Now, this black coal is the last coal to have been deposited anywhere on Earth in the Permian.
50:46The last of the great Gondwannon Glossopterus swamps.
50:50But it also marks the bitter end for over 80% of all species alive on the planet at the
50:57time.
50:58This truly was the world's greatest cataclysm.
51:07This figure is conservative.
51:11Some estimates have 95% of all species dead and gone.
51:17Wiped out in a geological blink.
51:30The trigger, it seems, did not come from outer space, but from underground.
51:38It's now thought massive volcanic eruptions in Siberia pushed CO2 levels sky-high and the planet into a runaway greenhouse
51:48crisis.
51:51These were the days when our living Earth nearly died.
51:58Acidified and stagnant, great swathes of the ocean festered.
52:04Toxic bacteria took over from plankton.
52:07And deadly hydrogen sulphide spilled into the skies.
52:16But with change, even of the calamitous kind, comes opportunity.
52:24And the Earth would soon echo to the thunder of giants.
52:34The adventure continues on NOVA's website, where you can watch other episodes of Australia's first four billion years.
52:41See video extras, hear from experts, and explore interactives.
52:45Find us at pbs.org slash NOVA.
52:48Follow us on Facebook and Twitter.
52:49On the next episode of Australia's first four billion years, dinosaur hunting down under.
52:55Big footprints. One there, another one there.
52:58Peer into the belly of a beast.
53:00And inside its stomach, we can see the vertebrae of its meal.
53:04Come face to face with bizarre creatures of a lost world.
53:09It's almost as if there's an independent experiment and evolution going on here.
53:13Monsters. Next time on Australia's first four billion years, on NOVA.
53:20Major funding for NOVA is provided by the following.
53:25The David H. Koch Fund for Science.
53:28Supporting NOVA and promoting public understanding of science.
53:34And by the Corporation for Public Broadcasting.
53:38And by contributions to your PBS station from viewers like you.
54:01This NOVA program is available on DVD and Blu-ray.
54:04To order, visit shoppbs.org or call 1-800-PLAY-PBS.
54:10NOVA is also available for download on iTunes.
54:14This NoVA programs is listed in the description.
54:42baptized.