DC_Amazing Earth_1of9_The Catastrophic Past
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00:00For over 4.5 billion years, the Earth has been blasted, burned, ripped and scoured.
00:20These phenomenal events have sculpted our planet through a series of devastating cataclysms.
00:34Understanding Earth's tumultuous history is like reading an intricate detective story,
00:39for the Earth is unlike any other planet.
00:43Its restless surface is changing constantly, destroying the evidence of the past, but if
00:49you know where to look for them, the clues are still there.
00:57I'm going to attempt to scoop a sample of molten lava.
01:00It will be extremely hot, we have to worry about gases and we have to worry about breakouts
01:04near the edge of the pond.
01:05The Atlantic Ocean owes its very existence to the geological violence that took place
01:18135 million years ago.
01:21The supercontinent began to split apart, and as it did so, there must have been a time
01:25when ocean waters rushed into the widening gap, forming a new ocean basin.
01:30What makes these caves particularly exciting is that they are one of the last unexplored
01:36frontiers, and turned out to be one of the world's largest and longest known cave systems.
01:46What I find truly remarkable is that within this core barrel is a massive piece of rock
01:51from 200 feet below the surface, and yet it contains as many bacteria in it as there are
01:56people on this planet.
01:58Ocean basins open and close.
02:00The sea covers the continents and then retreats.
02:03Mountain ranges like the Himalayas and the Andes will be eroded flat.
02:08On a human time scale, not much changes, but on a geological time scale, the whole earth
02:13is remodeled, and all the things that we've done and made will be destroyed.
02:18About 18,000 meteorites hit the earth every year, hurtling down at 70,000 miles an hour.
02:25Most are small and do little damage, but each brings clues to the catastrophic formation
02:30of our planet.
02:32Geologist Roger Buell, who has been working on this project for many years, says that
02:37the meteorites hit the earth every year are the most destructive.
02:42But each brings clues to the catastrophic formation of our planet.
02:46Geologist Roger Buell is working in northwestern Australia.
02:52Even though it's just arrived, this is the oldest thing on earth.
02:57It's a chondrite, a type of stony meteorite, and it's been wandering around the solar system
03:03for about four and a half thousand million years.
03:07It's stuff like this that the earth is made of, space junk glued together.
03:154.6 billion years ago, the molten earth grew as a continual rain of mega-meteorites
03:21pummeled it on its orbit around the sun.
03:26Each strike brought with it raw rock, the material from which earth could grow.
03:31It also brought explosive energy, raising the surface temperature of the primitive planet
03:36to over 1,800 degrees.
03:39A vast ocean of molten rock 100 miles deep covered the globe.
03:46Internal radioactivity raised the temperature even further.
03:50Earth became a melting pot, soon passing the melting point of iron.
03:55The meteoric iron began to sink to the center, dragged by the relentless tug of gravity.
04:01A kilometer sphere of molten iron would make the journey from the surface
04:07to the center of the earth in less than a million years, a blink of geological time.
04:15The constituents of the earth were forming.
04:19It had an iron core surrounded by molten rock.
04:23On the surface, a thin crust was developing.
04:27It behaved like these molten lava ponds, and the turbulent forces beneath
04:32began to fracture the crust.
04:38These are the tectonic plates, vast sheets of the earth's crust moving endlessly,
04:43tearing and crashing over the planet's surface.
04:47The process is still going on.
04:52In some places, the plates are forced apart and molten lava is driven through the seams
04:56to create new crust.
05:00Elsewhere, crust is destroyed where plates collide.
05:04One is forced back into the molten mass beneath.
05:08Along these subduction zones, volcanoes erupt.
05:16Soon after its violent beginning, the planet was to suffer the most ferocious assault imaginable.
05:26A rogue asteroid bigger than Mars smashed into it with enough power
05:30to blast much of the earth's surface into space.
05:34The debris was drawn together by gravitational forces and formed a protolunar disk.
05:40From that, the new moon grew rapidly, sweeping up the debris in orbit around the earth.
05:47Computer models suggest it only took a year for the fragments in orbit
05:51to coalesce and form a single moon.
05:55Professor Michael Rampino of New York University knows its history mirrors our own violent early years.
06:01This is the Clark Telescope at the Lowell Observatory in Flagstaff, Arizona.
06:05It's a telescope that was used to take pictures of the moon
06:09in preparation for the Apollo moon landings.
06:13To see the moon tonight, we need the telescope up in this position.
06:19We can make some fine adjustments.
06:25The density of the craters on the moon's surface was measured
06:29using the photographs taken by the Clark Telescope.
06:33What's more, the astronauts visited some of these regions in their six Apollo missions.
06:37Man, does this thing have steep walls.
06:41They said 60 degrees.
06:45Now I tell you, I can't see to the bottom of it and I'm as close to the edge as I'm going to get.
06:49That's the truth.
06:53The largest impact feature on the moon, the Imbrium Basin,
06:57is more than 1,000 kilometers across and was produced by the impact of a comet or asteroid
07:01more than 100 kilometers across.
07:05The basin is surrounded by mountains more than 5 miles high.
07:09This is where the Apollo 15 astronauts landed and took samples.
07:13They showed that these mountains are not like the mountains on the Earth,
07:17but they're piles of rubble, fragmented rock thrown out by this giant impact.
07:21Look at that. Guess what we just found.
07:25I think we found what we came for. Crystal rock, huh?
07:29Yes, sir. You better believe it.
07:33The pristine moon rocks that were brought back by the Apollo astronauts when radiometrically dated and studied,
07:37and they show that impact has been an important process in the formation and evolution of the Earth-like planets.
07:41What's more, the radiometric dating of the rocks
07:45has shown that the moon underwent a hellish bombardment
07:494 billion years ago.
07:53After that time, the bombardment died down.
07:57By that time, most of the asteroids moving around in the inner solar system
08:01had collided with the planets, and the process of formation of the planets was over.
08:05Three and a half billion years ago,
08:09the Earth began to cool.
08:13Water vapor and acidic gases were being released from the hot interior
08:17This was the Earth's big bulb.
08:21The result was a thick, steamy atmosphere with pressures 100 times greater
08:25than they are today.
08:29The only landscapes were volcanic frozen lava
08:33and yellow ash. There was no surface water.
08:37This harsh terrain had yet to be sculpted by erosion.
08:41There was moisture in the atmosphere, condensing in pockets,
08:45to create oceans or rivers.
08:55There was no oxygen in the air.
08:59It was inhospitable with no trace of life.
09:03A new theory suggests that in time, water may be enough to fill the world's oceans
09:07arrived from deep space, brought on ice comets.
09:11Cosmic rain continues today
09:15with small 20 to 40 ton ice comets striking the Earth's atmosphere
09:19once every three seconds. They add one inch of water
09:23over the entire surface of the globe every 20,000 years.
09:27When the atmosphere was saturated,
09:31the rain began.
09:41Over the eons,
09:45the torrential storms produced the greatest floods
09:49the planet has ever known.
09:53An endless ocean grew, and when the skies finally cleared,
09:57the Earth had been transformed into a watery globe.
10:01This is the time when life is thought to have begun.
10:05Echoes of those beginnings can still be heard today.
10:09Our most ancient ancestors,
10:13the most resilient creatures ever evolved,
10:17have survived unchanged for billions of years,
10:21living in solid rock.
10:25The Earth's oceans have been the source of life
10:29for thousands of years.
10:33Drilling to great depths into the rocks
10:37at Idaho Falls, Princeton microbiologist Tullis Onstott
10:41is hoping to take a closer look at their descendants.
10:45What I find truly remarkable is that within this
10:49core barrel is a massive piece of rock from 200 feet below the surface
10:53and yet it contains as many bacteria in it as there are people
10:57on this planet. Now these are living bacteria
11:01and they live at temperatures approaching the boiling point of water.
11:05They live at pressures that are 100 times the atmosphere.
11:09They live in a salty, briny solution that's alkaline
11:13and contains gases that are toxic to us, and yet they still manage to survive.
11:17They're known as extremophiles because of their
11:21extreme living conditions. To get a closer look,
11:25the scientists first extract them from their rocky home.
11:29They're the most primitive organisms on the Earth
11:33and the fossil evidence in the most ancient rocks on Earth
11:37indicate that these types of organisms must have existed 3.7 billion years ago.
11:41With skill and care, the team work inside glove boxes.
11:45Here they can manipulate the sample under sterile conditions.
11:53They go to great lengths to ensure that the only bacteria
11:57inside the tent are those that have made the journey up from the Earth.
12:01We need to pare away the outside
12:05of the core so that we can remove any
12:09contamination that may have occurred during the process of coring
12:13in the field.
12:17The core is then placed in a press and crushed to a fine powder.
12:22Then a sample is taken
12:26from the powder and a culture developed of the bacteria.
12:30These are the earliest common ancestors of all life,
12:34a colony of extremophiles.
12:38Observing how microbes survive thousands of feet below the surface,
12:42some scientists have speculated about life elsewhere.
12:46Could there be tiny extraterrestrials buried in the same way
12:50on other planets that appear outwardly sterile?
12:58The same kind of bacterial life was finding an equally unlikely home
13:02in the deep oceans of the primitive Earth.
13:06Water welling up from deep below the ocean floor must have carried the
13:10microorganisms into a warm volcanic crucible.
13:14Nearly 9,000 feet down,
13:18the sea floor is split into the great mid-ocean ridges.
13:22The crust is very thin, and the volcanic heat
13:26from the Earth's core heats the water, which floods out through black smokers.
13:30Here, strange communities of
13:34microorganisms thrive on the chemically rich mixture.
13:38These bacteria endure pressures 3,000 to 4,000 times greater
13:42than those on the surface, and support a bizarre array of creatures.
13:50They can survive here because of the heat escaping from the molten core
13:54only a few miles beneath. It's not only life that began
13:58here, but the actual fabric of the land itself.
14:02Where the tectonic plates that form the ocean floor
14:06are torn apart, new lava continually emerges,
14:10and new volcanoes are born.
14:18In 1963, this act of creation could be seen by all.
14:22Some 10 billion square feet of lava erupted off the coast of Iceland
14:26to form the new island of Surtsey.
14:30It emerged in a matter of days, just like volcanic islands
14:34on the primitive Earth.
14:38All over the planet, these islands appeared, and in time,
14:42they were to form the first continents.
14:46Clues as to how this happened are found in the Canadian Rocky Mountains.
14:50The outer shell of Earth, the lithosphere, carries
14:54the continents. It's made up of great stratas of different rocks
14:58extending 60 miles down into the Earth. Most of its structure
15:02is unknown. The deepest man has ever drilled is 9 miles.
15:06But the deeper needs a different approach.
15:12To discover just how their land was formed, a team of 700 scientists,
15:16the modern equivalents of early mapmakers,
15:20are charting this invisible territory.
15:24They use shockwave detectors, geophones, which the teams are placing
15:28all over the landscape.
15:32This is the world's biggest subsurface exploration experiment,
15:36the lithoprobe. In the Yukon province, the chief scientist is
15:40Charlie Roots.
15:44Geologists who work in sedimentary rocks are used to continuity,
15:48both in oldest rocks to youngest rocks, as well as being able to take
15:52the same rock formation for a long distance. You can't do it in these mountains.
15:56The rocks on the surface indicate
16:00a large platform of limestone, and the surrounding areas
16:04are rocks that have no relation to that. They are bits that are not part of the continent
16:08that appear to have come from somewhere else.
16:12These canyons show the folds and the twists of the rocks
16:16have undergone as they've been pushed up against the ancient continent.
16:20The problem is that we only get to
16:24see the rocks that are at the surface, and in an area where rocks
16:28are deeply dipping, there is far more of the story buried beneath our feet.
16:32To send shockwaves deep into the crust,
16:36200 pounds of explosive are buried in the ground.
16:44We're digging three holes for the geophones
16:48that we're going to be putting in here, so that we can have a three-component
16:52orientation system to measure the seismic wave that comes in.
16:56We have a vertical geophone, which will measure the vertical component of the arriving wave.
17:04There is a north-south geophone that will measure the north-south
17:08component of the incoming wave.
17:12And we have an east-west geophone to measure the east-west
17:16component of the incoming seismic wave.
17:2010, 9, 8,
17:247, 6, 5, 4,
17:283, 2, 1...
17:40As the shockwave races down through the ground,
17:44they hit something hard, much harder than the surrounding rock.
17:48The shockwaves are reflected and speed back
17:52to the surface, taking their precious information to the geophones.
17:56Analysis of the results shows that under the rockies
18:00are the buried remains of ancient volcanic islands.
18:04Over the last 200 million years,
18:08hundreds of these islands were grafted onto the North American continent.
18:12They form much of the land
18:16west of the Rockies, stretching from Mexico to Alaska.
18:20This is a clue as to how the first land masses were created.
18:24But until very recently, science was at a loss to say just
18:28when it happened.
18:32Then one day, prospecting for minerals in northwestern
18:36Australia, Roger Buick made a startling discovery.
18:40This rock is part of the oldest land surface on Earth.
18:44It has miraculously survived the never-ending cycle of formation
18:48and destruction of the crust.
18:52The vertical stripes have endured for over 3.6 billion years,
18:56giving a date for when the land began.
19:02Nearby, in the younger sedimentary rocks of the Karajini,
19:06are all the clues to solve another chapter of Earth's history.
19:10This was the first place where life and the land
19:14began to interact, and the traces are clear to this day.
19:18The impressive thing about the place is how red it is.
19:22In fact, red rocks stretch for
19:26hundreds of miles in every direction.
19:30The reason they're red is because of this red mineral,
19:34hematite, iron oxide, or rust.
19:38And the way they formed was when dissolved iron
19:42in the ocean combined with oxygen
19:46and precipitated out as iron oxide settled down to the
19:50seafloor and accumulated on the bottom of the sea.
19:54Initially, the atmosphere of the Earth had no
19:58oxygen. The same applied to the oceans. These rocks
20:02record an intermediate period, when there was still no oxygen in the
20:06atmosphere, but the upper layers of the ocean contained
20:10oxygen. There's a huge amount
20:14of iron oxide here. The sheer volume suggests that
20:18the oxygen could only have had one plausible source.
20:22Biology. Living organisms excreting
20:26oxygen as a by-product of photosynthesis.
20:30After 2 billion years, the oxygen had finally combined
20:34with all the iron. For the first time, free oxygen was able to
20:38escape into the atmosphere, and the air became breathable.
20:44Deep into the Australian outback is more evidence of primitive
20:48oxygen-producing organisms. In a secret location, Buick
20:52discovered are some of the world's oldest and rarest fossils.
20:56What I've done is step back more than three-quarters
21:00of the way back to the beginning of Earth history. And here
21:04are wrinkly layered sediments that occasionally
21:08dome upwards. These are stromatolites.
21:12Sedimentary structures created by
21:16filamentous microorganisms, trapping sand and mud between
21:20their little filaments. Those microorganisms were probably
21:24photosynthetic. The layers thicken over the tops
21:28of these domes, competing with each other to get nearer the sunlight.
21:32Now these stromatolites are remarkable
21:36for their great age, 3,450 million years old.
21:40Not only are they remarkable for that, but
21:44we can also infer something about the environment in which they lived.
21:48Just back here
21:52are gypsum daisies, little star-shaped clusters
21:56of gypsum crystals, calcium sulphate.
22:00These form when seawater evaporates in a shallow pond
22:04near the edge of the sea.
22:08By producing oxygen, stromatolites change the planet
22:12forever. These tiny bacteria were the first organisms to live
22:16together in colonies. They capture and incorporate
22:20fine sand to create rocky structures which still survive in Australia
22:24today. Living stromatolites only grow when they're almost permanently
22:28submerged in water, so you only see them exposed at very low tide.
22:32These grew here about 5,000 years ago
22:36when the sea level was about a metre or so higher.
22:40The living carpet of bacteria that formed them died off
22:44as the sea level gradually dropped, and the sediment that the bacteria
22:48trapped was turned into limestone.
22:54Life flourished
22:58and became a force to shape the world.
23:02In Utah, the shells of countless millions of marine
23:06creatures which lived and died here have been exposed
23:10where the San Juan River creates a great tear in the Earth's crust.
23:14The river has revealed a lost world
23:18where shallow seas once lapped the shores of the world's only landmass,
23:22the ancient supercontinent Pangea.
23:30200 million years ago, the Colorado Plateau was a desert
23:34in equatorial Pangea, the supercontinent which stretched
23:38unbroken from pole to pole.
23:4650 million years ago, this entire region underwent a cataclysmic change.
23:50Erosion began relentlessly stripping away layer upon layer
23:54of rock. The tectonic forces which squeezed
23:58compressed and lifted the land were locked in an endless battle
24:02with erosional forces, carving the land flat again
24:06shaping fantastic landscapes.
24:14Volcanic rocks that never managed to force their way to the surface are revealed.
24:19The granite was formed when the land was buried under a mile of sandstone.
24:23Erosion scrubs away the surrounding softer
24:27sedimentary rock, leaving the hard, igneous bones
24:31of the emerging hills.
24:37Water is the strongest force of all.
24:41It cuts through solid rock to create deep canyons.
24:45With terrible patience, it will
24:49scour away the stone and shape the rocks.
24:59One day, in an unimaginably distant future,
25:03Antelope Slot Canyon will be as wide and as deep
25:07as the Grand Canyon itself.
25:15The thousand foot high
25:19sandstone pillars, buttes and mesas that rise above the plains
25:23are the memorials to millions of years of the geological battle.
25:27But they too will disappear.
25:31Nothing can withstand erosion.
25:35As fast as tectonic forces raise landscapes,
25:39wind, rain and gravity will erode them down again.
25:43This is the story of the Antelope Slot Canyon.
26:01Sculpting the surface, gouging out the deepest ravines,
26:05cutting down the tallest mountains, nature finds its own
26:09equilibrium. In the end, it will obliterate
26:13all the structures the earth creates.
26:17200 million years ago,
26:21the supercontinent Pangaea began to split in two.
26:25It took 65 million years.
26:29Two continents we know today were shaped by another upheaval
26:33that hit the remains of the supercontinent in the south.
26:37In the jungles of South America,
26:41I found one of the most remarkable features on the face of the planet.
26:45This whole landscape owes its existence to this violent chapter of earth's history.
26:49The arctic climate, the climate of the Arctic,
26:53the climate of the Arctic Ocean,
26:57the climate of the Arctic Ocean,
27:01the climate of the Arctic Ocean,
27:05the climate of the Arctic Ocean
27:09is the violent chapter of the earth's history.
27:13The hope of finding more clues to this catastrophe
27:17has drawn Professor Michael Rampino here
27:21Iguazu Falls, Argentina. For me, the most spectacular waterfalls in the world,
27:25not only because of the spectacular scenery here,
27:29the 250-foot-high waterfall a mile wide,
27:33335 million years ago.
27:38The geological evidence is here in these rocks.
27:41This is basalt, a hard volcanic rock,
27:44stained red by iron oxide,
27:46oxidation of the iron within the rock.
27:48In fact, we're standing here at the base
27:51of a basaltic lava flow more than 100 feet thick,
27:54just one of many lava flows in this area
27:58which form a pile of lava more than a mile thick.
28:02In fact, in the waterfalls,
28:03one can see steps of the waterfalls
28:06which shows the individual lava flows in this pile.
28:22Imagine volcanic eruptions so enormous
28:24as to produce lava flows erupting
28:27from giant cracks and fissures in the Earth's crust,
28:29flowing out over an area
28:31twice the size of the state of Texas,
28:33more than 250,000 square miles.
28:36An enormous volcanic event.
28:39Massive amounts of sulfur-rich gases
28:41spewing into the atmosphere,
28:43droplets of sulfuric acid forming a veil
28:45that cuts out the sunlight and cools the climate,
28:48sulfuric acid rain killing the vegetation,
28:50the makings of an environmental disaster
28:52of enormous proportions.
28:53This is 135 million years ago,
28:56at the end of the Jurassic period of geological time,
28:58a time when there were mass extinctions
29:00of many forms of life.
29:03There's evidence here in these rocks
29:04for even more dramatic event in the history of the Earth.
29:15And here is just the piece of evidence that I need.
29:17On the other side of the world, across the Atlantic Ocean,
29:20is the world's most ancient desert.
29:22It dominates most of the southern African country of Namibia.
29:26I've travelled more than 4,000 miles,
29:28and the rocks are exactly the same.
29:31They're basalts, and they age as 135 million years.
29:36I've got a couple of days left before I go back to the desert.
29:39I'm going to try and find a way to get to the bottom of the Amazon.
29:42I'm going to look for the most ancient rock.
29:46I'm going to go through this area,
29:48and I'm going to try to find a way to get to the bottom of the ocean.
29:51their basalts, and the age is 135 million years.
29:55Clearly, when these rocks were erupted,
29:57as floods of lava traveling hundreds of miles,
30:00South America and Africa were together as one supercontinent.
30:06The Atlantic Ocean, which now divides Africa and South America,
30:10owes its very existence to this geological cataclysm
30:14that tore Pangaea apart.
30:16The supercontinent looked like this,
30:19made up of the present-day continents of Africa,
30:22South America, India, Antarctica, and Australia.
30:28The cracking started here and split the continent
30:31into the present-day continents of South America and Africa.
30:42In geological terms, it happened incredibly fast.
30:45The crack opened northwards at a speed of 2 inches per year,
30:49the split unzipping the land as it went along.
30:53Fountains of volcanic fire leapt through the crack.
30:57The entire process took only 5 million years to complete.
31:02Evidence of the unzipping is clear.
31:05The shorelines of South America and Africa match perfectly,
31:09and under the ocean, the Mid-Atlantic Ridge
31:12divides the two continents almost exactly down the middle,
31:16where it still pushes them apart.
31:18But geological upheavals can spell disaster.
31:22There have been five key mass extinctions in Earth's history.
31:26Best known are the dinosaurs.
31:29Why did they simply disappear from the face of the Earth?
31:35India may provide the answer.
31:3765 million years ago,
31:39there was still an island drifting towards Asia.
31:42This was when the layered landscapes of the Deccan Traps were created.
31:46A great volcanic rift spewed out half a million square miles of lava.
31:51Layer after layer of lava lies on the land in places up to 8,000 feet thick.
32:00Some scientists believe that the scale of this volcanic activity
32:04was so great it killed off the dinosaurs.
32:07Professor Michael Rampino thinks the traps were triggered
32:10by an extraterrestrial visitor.
32:13This is the Hoba iron meteorite in Namibia.
32:16It's the largest meteorite known on Earth.
32:18And like most meteorites, it contains the rare element iridium.
32:23And iridium has proven to be the clue, the connection,
32:26between the impact event and the extinction of the dinosaurs.
32:30Iridium is found near impact craters,
32:33but is extremely rare elsewhere in the Earth's crust.
32:36At these craters, the levels of iridium are 10,000 times higher than normal.
32:41Such high concentrations have been found in the sedimentary record
32:45all over the world at a consistent date of 65 million years ago.
32:50Recently, a crater more than 110 miles wide
32:54was detected off the coast of Mexico's Yucatan Peninsula.
32:57It, too, was created 65 million years ago.
33:02It was formed by a 10-mile-wide cosmic killer
33:06which closed on Earth at more than 60,000 miles an hour.
33:15It struck with the violence of the world's entire nuclear arsenal
33:19exploding a thousand times over.
33:21It sent out a ferocious fireball,
33:24engulfing the land for thousands of miles around.
33:27Enormous fires raged for months, destroying everything in their path.
33:36The impact may have had other catastrophic effects as well.
33:39The force was so great that shockwaves went out
33:42from the point of impact in Mexico around the world
33:45and focused and concentrated at the exact opposite point of the Earth,
33:48in the Indian Ocean.
33:52The exact opposite point in those days was the island of India,
33:56where Pino believes the violent volcanic eruptions
33:59which created the Deccan Traps was triggered by the meteorite.
34:03The effects of the impact explosion and the volcanic flood
34:07poured millions of tons of dust and ash into the air,
34:10plunging the world into darkness.
34:14Nitrogen, sulfur, and oxygen in the atmosphere
34:17combined to form acid rain as the Earth cooled.
34:21In this cosmic winter, 75% of all living things perished.
34:26When the skies cleared, the dinosaurs had gone.
34:33India continued on its race towards Eurasia.
34:36About 45 million years ago,
34:38they crashed together and began the fight for supremacy.
34:42Neither would give way.
34:44Too buoyant to be drawn back into the molten center of the Earth,
34:47they crumpled, folded, and doubled,
34:50leaving the crust only one way to go, skywards.
34:57The early Himalayan mountain chain
34:59was raised from sea level to five miles high
35:02as India penetrated a distance of more than a thousand miles into Asia.
35:07At about this time, the Earth started to get much colder.
35:12There is evidence for many ice ages during Earth's history,
35:16but the last full and most severe one began 45 million years ago,
35:21just as the Himalayas were being formed.
35:24One theory attributes the dramatic cooling to this tectonic turmoil.
35:33The collision raised the ocean floor
35:35and with it limestone high into the atmosphere,
35:38exposing it to erosion.
35:40The mountains are littered with limestone rocks and rubble.
35:43This debris would combine with rain and carbon dioxide in the air
35:47in a chemical reaction
35:49which removed millions of tons of the gas from the atmosphere.
35:53With less greenhouse gas to keep it warm,
35:56the entire planet would cool, triggering the Ice Age.
36:06The poles were now permanently covered by ice over two miles thick.
36:11At the edge of the vast ice sheets,
36:13immense glaciers advanced relentlessly.
36:16Nothing could resist as they raced forward
36:19at speeds of up to ten feet per day.
36:36As the ice covered more land,
36:38so more of the sun's heat was reflected back into space,
36:42chilling the planet further.
36:44At its coldest,
36:45Earth was covered by three times the volume of ice on the planet today.
36:51This ice locked the water away, trapping it on the land.
36:54With less available water,
36:56the world's sea level dropped by 425 feet.
37:01Today, the Caribbean island of Grand Bahama
37:04holds the clearest clues to the dramatic change in past sea levels.
37:08Microbiologist Steffi Schwab has been piecing the story together.
37:15Hidden deep in a mosquito-ridden mangrove swamp
37:18is a tannin-stained pool,
37:20an unlikely entrance to a mysterious ancient world.
37:25These caves have a story to tell
37:27concerning past sea level fluctuation
37:30and past interglacial and glacial periods.
37:44The first caves were found in the Pacific Ocean.
37:47They were found in the mid-19th century
37:49and were called the Caves of the Cascades.
37:53What makes these caves particularly exciting is that they are one of the last unexplored
38:04frontiers and they turned out to be one of the world's largest and longest known cave
38:09systems.
38:10We move from the entrance into a very large cathedral room where we can see the ceiling
38:22comes up to what we commonly call these cave systems which is a blue hole.
38:32You always find when you go into these large cathedral rooms a very large rock pile in
38:38the center and usually the collapse happens when the water is no longer in the cave supporting
38:44the ceiling.
38:48I'm now swimming through what is called a mixing zone and this is where the fresh water
38:57mixes with the sea water and causes what we call a shimmer.
39:09This mixing zone is responsible for aggressively attacking the wall rock, it's like soft cheese.
39:26Normally limestone could not be removed with your finger, you would need a rock hammer
39:31and a chisel.
39:36This is how we know that the caves have formed hundreds of thousands of years ago but we
39:41also know by evidence that we have found that the caves have been dry in the past.
39:47Twenty meters down further into the cave system are these bat droppings that have been fossilized
39:53and we know the only way that this can happen is when the caves are dry because bats do
39:58not swim and when bats roost in the ceiling the droppings collect on the rock and they
40:04become very hard.
40:09Deeper into the cave system we find another bit of evidence and that is this red Saharan
40:14dust which gets blown into the stratosphere during frequent storms which occur in the
40:19Sahara desert and will actually find its way into these caves.
40:25Most likely it's happened during periods when the cave was dry.
40:34The final bit of evidence which supports the fact that the caves have been dry are these
40:39beautiful stalactites and stalagmite gardens that we find at 28 meters plus.
40:49Stalagmites and stalagmites form during the ice ages and have formed over a period of
40:54hundreds of thousands of years.
40:58What happens is the water is frozen in the ice caps on the poles, sea level drops and
41:05the caves become dry and usually during ice ages it rains a great deal more in the tropical
41:12regions of the world.
41:16This rain water percolates through the bedrock or the ceiling rock and dissolves the rock
41:21that's there and it comes out in the drip water and crystallizes just like an icicle
41:26and basically these are rock icicles.
41:46The ice ages affected and shaped the landscapes but sometimes the clues are so gigantic it's
42:04hard to recognize them.
42:07In Washington state in the Grand Coulee Canyon are the channeled scab lands.
42:11For years a succession of scientists tried to work out what could have caused erosion
42:16on this scale.
42:17USGS scientist Richard Waite is the latest investigator.
42:22This rock the size of a three story house looks like it's part of the bedrock, part
42:27of this basalt that forms this vast landscape.
42:31But the structure in the basalt is horizontal as you can see whereas the structure in this
42:35rock is vertical.
42:36In other words this big rock has been moved.
42:40The rock can't have just simply rolled off the cliff, we're too far from it and there's
42:43a valley between us and it.
42:46Glaciers have been known to move rocks this size but we are beyond the glacial limit.
42:52But the biggest clue in the landscape is the landscape itself.
42:59This gorge is carved in basalt, one of the hardest of rocks, it ends in a sheer cliff
43:04400 feet high and it's in the shape of an enormous horseshoe.
43:10It's like the gorge below Niagara Falls but this, Dry Falls, is fully two Niagara's high
43:16and three wide and yet this gorge and these vanished falls, enormous as they are, are
43:22just but one element in a large landscape.
43:27Waite is continuing the work begun by geologist J. Harlan Bretz in 1923.
43:32Bretz was the first to say that this entire landscape was a gigantic river bed formed
43:37by 3,000 square miles of the Columbia Plateau being swept away.
43:42No one believed him because the scale was so huge but he was certain that the only explanation
43:48for this scale of damage was an enormous flood.
43:51The whole area was obliterated and changed forever as the torrent flooded through.
43:57Even on the top of the cliffs, the water was over a hundred feet deep.
44:01One of the things we see when we get down flying in the cataract, we're about a hundred
44:08feet below the level of the water, is the enormity of this cataract.
44:13The walls extend for miles, many miles, 17 miles in fact, continuous vertical cliffs
44:20in basalt.
44:23The basalt cliffs are amongst the hardest structures found in nature, resistant to weathering
44:28and erosion.
44:29These walls could only have been cut by an enormous body of water.
44:37One by one, these columns of frozen lava were quarried from the rock face and carried away
44:41by the raging torrent, causing the wall to retreat and the cataract to widen.
44:48So it was accepted that this is how the channeled scablands were shaped.
44:52But an important part of the mystery remained.
44:55Just where could all that colossal, earth-shattering volume of water have come from?
45:00A hundred miles to the east, geologist Joseph T. Pardee had described an enormous ice age
45:06lake, Glacier Lake, Missoula.
45:09This lake held in some 600 cubic miles of water.
45:12600 cubic miles is all of present-day Lake Erie, plus all Lake Ontario.
45:19The lake was held in by an ice dam that had crossed the Clark Fork River and dammed it.
45:24The lake rose 2,000 feet deep against the side of the ice dam, but there was no evidence
45:29to link the lake with the channeled scabland.
45:34In 1939, Pardee discovered a series of giant ripples.
45:39These are like sand ripples on the beach, but they are of enormous size, hundreds of
45:43feet apart, 10 feet high and more, and they are composed of gravel.
45:49Such a feature could only indicate a swift outflow from Glacier Lake, Missoula.
45:56The gigantic ice dam held back the water until it reached a critical level.
46:05When it was 1,800 feet deep, the pressure of the water was so immense that it forced
46:10its way through the base of the ice dam.
46:16Having found a weakness, the icy waters raced on, widening the split and weakening the dam
46:21catastrophically.
46:23The waters of the entire lake were released in a devastating discharge.
46:30This discharge was 10 times the flow of all the world's rivers.
46:34That's almost beyond belief.
46:36This great discharge was headed straight towards Bretz's channeled scabland.
46:41Still, parts of this great mystery remained unsettled.
46:45For instance, what if this great 17-mile gorge below Dry Falls?
46:50According to Bretz's idea, this whole 17 miles would have to be excavated in one flood.
46:56One thing Bretz's critics objected to was the enormous scale of erosion so swiftly.
47:01More water, they wanted, over far more time.
47:06The answer was found by chance 200 miles away in the Walla Walla Valley.
47:11In 1926, a freak flood created a 100-foot deep canyon.
47:16It revealed many layers of silt.
47:20Waite realized that this area must have been in the path of the great floodwaters that
47:24formed the channeled scablands.
47:27Each one of these beds has a distinctive pattern of sedimentation.
47:32Each bed begins with a coarse sand at the bottom, and then it grades up to a medium
47:37sand, and then finally a silt, and it happens again and again and again, each layer.
47:44This white layer here is an ash that we know is from Mount St. Helens.
47:49We've analyzed it chemically, meteorologically, and it clearly came from Mount St. Helens.
47:55We know its date.
47:56By radiocarbon dating, we know that this is 15,000 years old, approximately.
48:01Therefore, we have a beautiful timeline running through this section of 15,000 years.
48:08The ash could only have fallen after the flood had passed and the sediment settled, yet it's
48:14covered by many layers of sediments, 39 in all.
48:20This was the final piece of evidence that explained the creation of the scablands.
48:25Here was more water over more time.
48:28The catastrophic outburst flood must have happened time and again.
48:34Once each flood had left its mark, the vast glacial dam would advance and the waters of
48:39Lake Missoula would start to rise again, continuing the cycle of flood followed by calm.
48:46Only when the time of the ice was over did the floods stop.
48:54The change from ice age to warmer times is governed by how close the Earth is to the
48:59sun.
49:00Every 100,000 years, the shape of the Earth's orbit around the sun changes.
49:07This has led some scientists to wonder if the recurring cycle of catastrophe and extinctions
49:12on our planet is governed by extraterrestrial forces.
49:17Mass extinctions and the catastrophes that caused them seem to follow a periodicity of
49:21about 30 million years.
49:23It's that cycle that suggests that the cause of a catastrophe lies outside the Earth.
49:28On a clear night here in Africa or in other places where you can see the night sky, we
49:32can see astronomical evidence for the cause of these geological catastrophes every 30
49:36million years.
49:42Our solar system is on a voyage through the disk-shaped Milky Way galaxy.
49:48Every 30 million years, we pass through the densest part of the galactic disk.
49:54During that time, the comets of our solar system can become disturbed and fall inward
49:58toward the inner planets.
50:00During this period, the Earth is more likely to be impacted.
50:13This cycle may explain the catastrophic history of the Earth.
50:17The last major mass extinction was 35 million years ago.
50:20We're in the densest part of the galactic disk now, and the next mass extinction may
50:24include us.
50:40Cataclysms may have caused extinctions and disasters, but they have also shaped the Earth
50:45and produced an environment in which human life could flourish.
50:50The air breathable, the seas are warm, climate mild, the ice rooted firmly at the poles.
50:57In fact, a geological truce.
51:00But that truce may be coming to an end.
51:04With man so widely spread across the planet, cataclysms of nature will turn into human
51:09catastrophes.
51:15The forces that drive the Earth are impervious to our needs.
51:19Every movement of the plates brings the danger of disaster nearer.
51:24We have to learn that our restless planet will never stand still.
52:15Transcription by ESO. Translation by —