tv PBS News Hour Weekend PBS July 20, 2014 5:30pm-6:01pm EDT
richard smith: over four billion years in the making. an island adrift in southern seas. it's australia, the giant down under. step ashore and you'll find a young nation with all the gifts of the modern age. but move beyond the cities and an ancient land awaits, one nearly as old as the earth itself. australia is a puzzle put together in prehistoric times.
and the clues that unlock the mystery can be found scattered across australia's sunburnt face. i'm richard smith, and this is an amazing country. i'll show you that every rock has a history, every creature a tale of survival against the odds. join me on an epic journey across a mighty continent and far back in time. of all continents on earth, none preserve the great saga of our planet and the evolution of life quite like this one. nowhere else can you so simply jump in a car and travel back to the dawn of time. in this episode, the beginning of it all.
from a cosmic maelstrom, a planet is born. this is no paradise, but somehow, life gains a toehold, then is nearly frozen out. this is the tale of the first australians, how they survived and flourished. from australia's ancient stones comes the story of our world. "australia's first four billion years: awakening," right now on nova. major funding for nova is provided by the following:
boeing-- where the drive to build something better inspires us every day. supportinova and promoting public understanding of science. and by the corporation for public broadcasting. and by contributions to your pbs station from: smith: the best way to understand the story of australia is to get out into it. feel the sun beating down on its ancient bones.
and i do mean ancient. to get a true appreciation of how old australia really is, you need to get a sense of deep time. okay, so this looks like a pretty ordinary four-wheel drive, but imagine just for a moment that it's fitted with a deep time drive. i simply dial up the time i want to go to, and by the magic of time-shifted gps, it does the rest. gps voice: you have selected "the beginning." smith: i've set the controls for a million years per minute. that's 60 million years of history for every hour we travel down the road. you want to see the real, old australia? it's quite a ride.
at a million years per minute, a blink of an eye sees us in an australia before europeans. a few seconds later and we pass the first aboriginal footprints. within minutes, you're dodging marsupials the size of minivans and dragons far longer. gps voice: caution, hazardous wildlife. smith: worried about roadkill? it gets worse. an hour down the road, and suddenly the land is dominated by dinosaurs. it will stay this way for the next three hours as we barrel back deep into the past. gps voice: recalculating deep time.
smith: over 250 million years down the road of time, about four hours at this speed, and it's the world before dinosaurs. even further and there is no life on land at all. i drive on. at 500 million years, about eight hours since we left the present day, all life is underwater and distinctly weird. but time is deep. there's still 90% of history to go. while the entire history of humanity occupied only the first few seconds of this journey and complex animals the first nine hours, i have to travel back over two and a half days at this speed
to reach the first stirrings of life. gps voice: caution: destination approaching. smith: finally, after over three days traveling at 60 million years an hour, i've driven back four and a half billion years. i have run out of road. we have arrived in the darkness at the edge of time. smith: when the first rays of the newborn sun shone out into space, they illuminated a scene of untold cosmic violence. swirling around the young star was a disc of dust and debris,
every fragment locked in mortal gravitational combat with every other lump of rock, metal, ice and dust in orbit. this is the process of gravitational cannibalism that marked the formation of all the planets, and the earth grew bigger and hotter with each conquest. the heat came not only from collision but from the natural radioactivity building up inside. then, just as the outer crust was beginning to harden, it's thought our planet was almost wiped out. another competitor, this one the size of mars, crossed earth's path. (explosion)
the aftermath was the formation of our pale airless companion, the moon, and the red-hot iron-rich ball of rock we know today as home. understanding the fiery birth of the earth really helps explain how the engine of our planet works. the crust i am sitting on might have cooled down, but the planet below all of us is still a hot ball of rock spinning around in cold space. and it's still trying to cool down. and as long as it cools, the continents we sit on continue to move. this is the engine of plate tectonics that's driven the story of our world since day one.
and for australia, we can pretty much date that first day. nearly two thousand billion sunrises after that first dawn, i'm heading west to one corner of the country that has faithfully kept a record of the earliest days of planet earth. so we're almost there. just in front of us there. smith: for decades, geologist simon wilde has been climbing the jack hills in western australia, date stamping the rly earth. wilde: this is the famous discovery outcrop.
this is the site where the world's oldest zircon crystals have been recorded. smith: though ancient, it's not the rocks themselves that are so old here, but the microscopic crystals of zircon within them. known in the gem trade as poor man's diamonds, zircon crystals form when molten rock cools in the earth's crust. and just like diamonds, zircons are forever. if you ever wanted to find a spot to ponder your oneness with the great age of the earth, you couldn't do better than this rock, because within it are the oldest remnants from the early earth ever found. older than you and i by a mere 4.4 billion years. at just a whisker younger than the age of the planet itself, this tiny treasure, zircon w74,
is the ultimate aussie survivor. recycled from rock to rock, zircons like w74 have resisted everything the planet has thrown at them. and yet they've somehow managed to keep a diary of the earliest days locked deep within their crystal lattice. reading that diary in the lab has been a revelation. (explosions) the oldest zircons, it seems, crystallized inside molten, continental granite that cooled rapidly in the presence of abundant liquid water. waves were probably breaking against the cooling shore of the future western australia within 150 million years of the earth's formation.
today's sun beats down here on tiny fragments of what may be our planet's oldest continent and much of the earth's most ancient rock. it's no surprise then that australia feels like an old, tough country. within a stone's throw of the jack hills is nearby mileura station. here, third-generation rancher patrick walsh ekes out a living from the oldest corner of an ancient land, a red and rocky heritage from the dawn of time. the geologists are up there getting terribly excited, bashing rocks.
oh, yeah, they're very excited. i always joke with them and say that that's the new g-spot in geology because you get a good laugh out of it and it is important. it did rewrite the geology books. that doesn't happen every day. smith: this new picture of the young earth is of a landscape you might have recognized-- rich in water, clouds and raw geology, but almost totally devoid of oxygen. if you were lucky enough to be able to travel back to the very earliest days of the planet, you would have been treated to some of the greatest shows on earth. but you would have needed a lot more than a hard hat and a gas mask
because this was a very dangerous world. we can tell from the heavy cratering on the moon at this time that the early earth must have been pounded to within an inch of its life. you can get a sense of what this must have been like by visiting wolfe creek crater in the kimberley. the great thing about wolfe creek crater is because it's so fresh, relatively speaking, it's a terrific place to see what sort of impact a big impact can make. when the object hit over there, it released so much energy that it set off an explosion the equivalent of an almighty nuclear blast. as the material came out, it literally flipped the rock
back onto itself around the edges. this sandstone is now leaning back, and everything that was in there either vaporized or was hurled out into the surrounding countryside. but wolfe creek crater was formed only recently by an object probably only a few yards across. combine at least one 30-mile-wide asteroid striking the earth every century with a corrosive, acidic atmosphere, and you probably have the reason why so little of the early earth survives. the craters of the moon show that the great bombardment slowed about 3.8 billion years ago. but while the moon's face has changed little, the archaean earth looked nothing like the world today.
none of our familiar continents. no green blush of life on land. but dive into those ancient australian seas and you would have found the first stirrings of life. it probably looked like this: slime. some of the earliest tantalizing signs of what could be fossilized bacteria appear in western australian rocks around 3.5 billion years ago, not long after the meteor bombardment ended. while the details of the origin of life remain shrouded by the mists of time, scientists are starting to get a fix on when and probably where it happened.
and one thing is for sure: the early earth had plenty of the raw ingredients. a reliable supply of water, heat and biologically useful chemicals could all be found close to volcanic vents, like in these hydrothermal pools in new zealand. this blistering water contains no free oxygen. instead, it's rich in poisons like hydrogen sulfide and arsenic. and rich in life, too. the orange scum lining the rocks is a jungle of primitive bacteria and archaic microorganisms, all feeding on the noxious goodies oozing from the hot earth below.
similar environments have existed in the sunless deep sea for billions of years. both habitats are home to the most primitive life-forms we know, and both are closely linked to the dynamic, tectonic world we now live on. wherever it started, life soon took hold in the sunlit shallows. and to see what it looked like, we need to head to the beach. the australian outback: bone dry and baking hot. hardly the sort of conditions you'd associate with the origin of life. but it's precisely because of this tough environment that down at the end of this road,
we can find a unique glimpse into the world at the dawn of life. if you ever wanted to pay a visit to your most distant ancestors, then shark bay in western australia is the place to do it. the high rates of evaporation here in hamelin pool make the shallow water twice as salty as the open sea, just the sort of tough, preserving conditions for slow-growing old-timers who prefer to be left alone. meet your most distant living relative: the stromatolite, still going strong here in the salty waters of shark bay. now, these guys might look more like rocks than your relatives, but you shouldn't be easily fooled.
on the outside is a vast living community of microscopic bacteria that have developed the knack of gluing mud into mounds. and they've achieved this with the revolutionary trick of harnessing the power of sunlight. photosynthis changed the world. no longer slaves to volcanic energy, light-harvesting bacteria began to spread to any sunlit surface in the sea. and growing as stromatolites, they could even make their own. it's the ultimate living rock. how the bacterial colonization of those distant shores began is a puzzle that scientist david flannery is keen to solve,
and a simple living algal mat offers a remarkable clue. it's much easier to interpret things in the fossil record if you have a modern example. here's a piece of rock from western australia in the pilbara that's 2.7 billion years old, and it has a very similar structure and it comes from a very similar environment. you can see the modern example is made up of these tuf and ridges and this polygonal pattern, and the fossil example is made up of the exact same stuff. smith: they may come in a range of shapes and sizes, but these high-rise bacterial communities have barely changed in billions of years. to swim here is to take a dip deep into the past. this is a time tourist's trip to a three-billion-year-old beach.
we know that stromatolites dominated the ancient australian shorelines because you can still visit them, preserved in the rocks of western australia's pilbara region. the town of marble bar, population about 350 plus a few dogs, claims the dubious distinction of being the hottest town in australia. it's probably why some joker dubbed this torrid little spot a few hours out of town "north pole."
geologists can read perhaps the oldest preserved planetary landscape in the rocks here: a coastline with beaches and sandbars. and something else. the gentle laminations in these rocks have been interpreted as the first tangible evidence of life. visible to the naked eye, these may be the world's oldest fossilized stromatolites, dated to nearly three and a half billion years. though the biological origin of the oldest fossils is still debated, the pilbara's rocky ranges are clearly awash with once-living stromatolites that in places must have formed extensive coastal reefs. as far as we can tell, this was the australian seaside circa three thousand million years ago.
stromatolites in the shallows. smoke on the horizon. fire in the sky. (bird cawing) these simple life-forms made their mark on the world in a far bigger way than as fossils in a landscape. they started making the landscape themselves. south of north pole lies another pilbara treasure: karijini national park. i'm taking a shortcut to the distant past.
the deeper i drop into iron-rich hancock gorge, the further back in time i travel. okay! down here, you can look back at one of the earth's great turning points. two and a half billion years ago, the atmosphere was still without oxygen. but beneath the waves, stromatolites and their photosynthetic kin were steadily releasing this reactive waste product into the water. it didn't get far. the oceans were full of dissolved iron left over from the planet's formation.