9.00pm Thursday 22nd February 2001
NARRATOR (DILLY BARLOW): There is a theory that scientists once
dismissed as absurd - that long ago the Earth became so cold every
inch of it was entombed in ice. The whole planet became one vast
snowball and it lasted for ten million years.
PROF. JOSEPH KIRSCHVINK (California Institute of Technology): The
image of a frozen, white Earth was probably the worst nightmare
I've personally ever come across. Death to an entire planet.
NARRATOR: For years the snowball theory has been dismissed as impossible.
The critics said if the snowball had struck all life would have
died and we would not exist.
PROF. GUY NARBONNE (Queen's University, Kingston, Ontario): The
problem with the snowball is that this should have been the greatest
environmental calamity of all time and yet we can't find the bodies.
NARRATOR: But a few defiant scientists have adopted the snowball
theory with religious ferocity and if they can prove it, they may
have found something to stun the world, a theory that may explain
the origins of complex life on our planet. Earth has no more terrible
force than an ice age. Only five times in its four billion year
existence has our planet suffered this kind of catastrophe. No one
is certain what started them or why they happened, but there is
one thing about ice ages on which most scientists agree. The conventional
view is that no matter how ferocious the advance of the cold in
any ice age there will always be parts of the world that are safe
and warm. The freeze spreads out slowly from the poles, but never
reaches the hottest part of the planet, the tropics. It has long
been assumed that this is a basic law of nature. The tropics can
never freeze. But then this basic law of nature can't explain what
happened 600 million years ago in Namibia. Paul Hoffman is one of
those defiant geologists who disputes the conventional view. He
has spent years trying to convince his colleagues about the snowball
PROF. PAUL HOFFMAN (Harvard University): As a scientist I was completely
convinced it was right, but I knew I was going to have a struggle
on my hands because any idea as radical as, as this is going to
be difficult to get across and there are going to be sceptics for
NARRATOR: The place Hoffman and his colleague, Dan Schrag, come
back to study again and again is Namibia. It is not an obvious place
in which to seek evidence of a catastrophic ice age. It is a land
of relentless heat, one of those locations that has been in the
ropics for hundreds of millions of years. The conventional laws
of nature say an ice age could never have penetrated here, but lurking
among the sun-baked rocks is something that the conventional laws
of nature cannot explain away. 600 million years ago these hills
were at the bottom of the ocean and lying on the old seabed are
mysterious boulders. Geologists call them drop stones and drop stones
could only have been brought here by one thing: a glacier. To recreate
drop stones in the lab first you need ice.
PROF. DANIEL SCHRAG (Harvard University): This is going to take
NARRATOR: The ice needs to float on shallow water above a sandy
sea floor. This is to simulate a glacier as it flows off the land
onto the surface of the sea. Because it has carved through the landscape
a glacier always collects a huge amount of rock debris.
DANIEL SCHRAG: The ice would then get filled up with all sorts of
boulders and cobbles and in this case we're just using some gravel
which we can form on top of this layer of ice in our tank here.
NARRATOR: Having recreated a boulder-filled glacier, you need to
melt the ice. As the ice melts the boulders are released.
DANIEL SCHRAG: When most of the ice has melted is a point you can
see that all the rocks the glacier's carried out to the ocean are
now dropped to the sea floor. In addition to all of this, in the
real world there'd also be a lot of sand and a lot of much finer
grain sediment and so these rocks would get filled in with very
fine grain sediment as well.
NARRATOR: In a few thousand years the fine grain sediment will cement
itself together to form rocks, with the boulders trapped inside
and that's how drop stones are made. All you need is a glacier.
The message from the drop stones suggests just one thing: Namibia
in the tropics, a place that everyone says has been hot for hundreds
of millions of years, must once have been covered in ice.
PAUL HOFFMAN: The most compelling evidence here is the juxtaposition
of a large boulder like this enclosed within very fine and delicately
layered sediment and so it's difficult, if not impossible, to imagine
any way to account for this other than a very extensive glaciation.
NARRATOR: But for 50 years, since the idea that an ice age must
have smothered the tropics was first proposed, it has been deemed
so radical that most scientists have dismissed it as absurd. The
theory has its roots in the 1940s when a young geologist called
Brian Harland made a series of intrepid field trips deep into the
BRIAN HARLAND (Cambridge University): Conditions were very different
then - manhauling in the old Scots tradition. It was cold but you
get used to it, you can get used to anything really.
NARRATOR: In the Arctic Harland had ample opportunity to learn all
there was to learn about that telltale sign of glaciation - drop
BRIAN HARLAND: Glacial deposits were very dramatic, currents very
distinctive, easy to identify and when I saw them I knew from my
own experience that this is glacial. I didn't have to think very
hard about it.
NARRATOR: But it was when he returned from the Arctic, armed with
this new-found knowledge, that Harland made his scientific breakthrough.
With his now expert eye, he analysed rocks from all over the world.
What he discovered amazed him. Almost everywhere he looked, in rocks
formed about 600 million years ago, he found drop stones: classic
evidence that there had once been thick ice even on the hottest
BRIAN HARLAND: There's no continent really without some glacial
record. You have them in different parts of Europe, in Africa, plenty
in Africa, not so well known in South America, but they have been
known later in North America.
NARRATOR: The drop stones were so widespread that Harland began
to contemplate the unthinkable.
BRIAN HARLAND: The fact is we've got evidence of a global glaciation.
NARRATOR: He knew it made no sense. He knew that at the peak of
the last Ice Age, which ended just 10,000 years ago, ice spread
down to where New York is today, but no further, but the evidence
was staring Harland in the face, evidence which seemed to flout
the laws of nature. 600 million years ago the drop stones said ice
had spread over every continent, right across the tropics to the
Equator itself. It meant there must have been an ice age of unimaginable
ferocity, in fact too unimaginable. When Harland presented his theory
of global glaciation colleagues dismissed it as laughable.
BRIAN HARLAND: There was a lot of scepticism. I don't think I was
ever shaken by it because I was pretty confident in my own observations,
but I was interested and a bit annoyed in a way that, that so many
people were hostile to the idea.
NARRATOR: The sceptics had a whole host of reasons why Harland had
to be wrong, reasons that were utterly convincing, as they were
based on the most basic rules about how the world works. For a start,
it's given that the tropics, that wide belt around the Earth, has
always received the full glare of the sun. As they have always basked
in sunlight, so they must always have remained warm. Even during
the last Ice Age geological evidence suggests the tropics were pleasantly
hot and they had another reason why the snowball theory must be
wrong. There was a far simpler explanation for drop stones in the
tropics, one that was absolutely consistent with scientific knowledge
and which didn't involve a ludicrous idea like the tropics freezing
over. Continents drift. They scrape across the surface of the Earth
at about the same pace that your fingernails grow. This means that
in about 400 million years continents can shift from one end of
the globe to the other. Obviously, the doubters said, 600 million
years ago all the continents had drifted into icy, polar regions.
Once there, glaciers would have formed and drop stones would be
common in all rocks of this era, and after those drop stones had
been formed at the poles the land, and the drop stones, would have
been carried back down to the tropics by continental drift. For
years this remained the accepted explanation for why drop stones
appeared everywhere. The only way to make the theory of a global
glaciation credible was for someone to make the impossible possible.
They would need to find a way for the tropics to freeze over, and
this is just what happened next. (RUSSIAN COUNTDOWN) It was the
1960s, the height of the Cold War. The world was obsessed with calculating
the odds of surviving a nuclear Holocaust. It was known that a series
of massive nuclear explosions would create clouds of dust, smoke
and soot. Sunlight would be blocked out. Hypothetically the Earth
would enter a nuclear winter, a man-made ice age. In the Soviet
Union finding out how severe this man-made ice age could be became
the task for one climatologist. Mikhail Budyko was that man.
PROF. MIKHAIL BUDYKO (State Hydrological Institute, St. Petersburg):
Long ago, probably 25 or 30 years, I compiled a number of studies
which could be used to describe origin of ice ages.
NARRATOR: What Budyko was to uncover would fly in the face of conventional
wisdom. He would show how those predictions that the tropics couldn't
freeze over were complacent and unfounded. Budyko knew that because
the land and oceans are dark they absorb most of the heat coming
from the Sun's rays and that is how our planet is warmed up; but
sheets of ice are white. They reflect sunlight like a mirror, so
an ice-covered Earth absorbs far less solar heat. During an ice
age as the freeze spreads the Earth grows whiter, more heat is reflected
away so less and less heat is absorbed and so the Earth grows ever
colder. It means that potentially the Earth could be caught in a
vicious circle of unstoppable freezing. Budyko converted this hypothetical
scenario into a mathematical formula and that formula produced a
terrifying prediction: the Earth's climate has a theoretical breaking
point. As long as the ice sheets remain close to the poles the Earth
is safe, but if the freeze continues, such as might happen in a
nuclear winter, they could advance down to about where Texas is
today. Once the freeze had reached that point so much of the Earth
would be covered in white ice that over half the solar heat that
normally warms the planet would be reflected back into space. At
that point there wouldn't be enough heat left to warm up the Earth.
Once this happens there could, in theory, be a runaway freeze, a
freeze that nothing can stop. Temperatures plummet, ice sheets spread
across all the continents, the oceans, and eventually even the tropics.
If this was ever to happen the entire planet would be trapped in
ice. There would be a snowball Earth. What was most disturbing about
Budyko's calculations was that an Earth encased in ice would reflect
so much solar heat it could never warm up enough to thaw, ever.
A snowball Earth would mean a world entombed in ice for eternity.
MIKHAIL BUDYKO: It was my opinion twenty years ago that such a system
will be stable for very long time and possibly all life will disappear.
NARRATOR: This was Budyko's paradox. He had shown that a runaway
freeze could ice over the tropics in theory, but he had also shown
that it could never have happened in practice because, if it had,
the world would still be a snowball today and that would mean we
would never have existed. For 15 years nobody could solve the paradox
of the runaway freeze. The snowball Earth theory remained a logical
impossibility. To resurrect the theory believers would have to do
two things. First, they had to prove that ice really had reached
the hottest parts of the planet, the tropics, and that the drop
stones hadn't arrived there merely through continental drift. Second,
they had to come up with a theory that offered an escape from the
runaway freeze. That was when a new scientist entered the picture.
In the late 70s Joe Kirschvink was one of geology's rising stars
and back then he thought the idea of a snowball Earth was mad.
JOSEPH KIRSCHVINK: The willingness to accept a nutty idea like freezing
the whole planet really needs to be supported by incredibly strong
evidence and overall if you had asked me to place a wager back in
the late 70s I would have been on the conservative side on that
NARRATOR: Kirschvink's conservatism came about because he believed
the simple, conventional explanation for why there were drop stones
at the Equator today. 600 million years ago, he thought, all the
continents must have been up near the icy poles when the drop stones
were formed. There was, however, only one technique for testing
their theory and it just so happened that Kirschvink had dedicated
his entire professional career to that technique. It involved magnets
and Kirschvink is a man in love with magnets.
JOSEPH KIRSCHVINK: I have wiped out my credit cards so many times
by playing with strong magnets I, I don't like to remember it.
NARRATOR: Few people realise it, but every rock is a weak magnet.
Each one contains magnetic minerals and the direction these minerals
pull in is fixed for ever the moment the rock is first formed and
what gives these minerals their magnetic direction is the magnetic
field round the Earth's core. This means that rocks formed at the
poles will always have a magnetic direction that points up and down.
Rocks formed at the Equator will always have a magnetic direction
that points from side to side.
JOSEPH KIRSCHVINK: Rocks have the ability to preserve magnetic direction
because of magnetic minerals in them. They act like little compass
needles and will line themselves up.
NARRATOR: By finding out a rock's magnetic direction Kirschvink
is able to identify where in the world it was originally formed,
no matter where continental drift might have taken it in the millions
of years that followed. In the 1980s Kirschvink heard of a team
of Australians who had run tests which, they claimed, showed evidence
of glaciers in the tropics. Ever the sceptic, Kirschvink decided
to duplicate their tests on his own, more sophisticated equipment.
It meant examining drop stones from some of the hottest parts of
the Earth. The question was: were they already at the Equator when
they were formed by the ice, or had they been created at the poles
and then carried to the tropics by continental drift? To answer
the question Kirschvink turned to his pride and joy: a custom built,
JOSEPH KIRSCHVINK: It's, it's an incredible instrument. You lower
the sample into the actual magnetometer chamber. The weak magnetic
field of the sample generates an electric current and so it allows
us to measure the magnetic moment of an extraordinarily weak magnet,
one billionth, say, the level of an ordinary hand magnet I think.
NARRATOR: Attached to the magnetometer was a computer which plotted
each rock's origin on an electronic outline of Earth as seen from
above. The centre of the circle represented the poles, the circumference
the Equator. If the drop stones had been formed at the poles, as
Kirschvink and everyone else thought, they would show up at the
centre of the circle on the computer. If they had been formed at
the Equator they would show up at the circle's edge. The machine
gave its answer: the drop stones had been formed in the tropics.
600 million years ago there must have been a snowball Earth. In
the late 80s Kirschvink adopted the snowball Earth theory with fanaticism
and if his findings flew in the face of existing theories about
the laws of nature then stuff those theories.
JOSEPH KIRSCHVINK: There's a fundamental theorem in science: if
the theory is in conflict with data modify the theory. There's so
many wonderful, beautiful theories that have been slaughtered by
a nasty little fact.
NARRATOR: But Kirschvink was racked by the insurmountable paradox
of the runaway freeze, that if a snowball Earth had ever happened
then science said we should still be entombed in ice today.
JOSEPH KIRSCHVINK: How do you get out of it? Obviously the climate
modellers had assumed that that was an irreversible step and that
you would never get out of it and yet we're out of it now and if
we had been in it before some point we must have gotten out of it.
NARRATOR: To get out of the deep freeze what Kirschvink needed was
a power that would stay hot, even when the whole planet had frozen
over, something that Budyko hadn't thought of, something that could
burn for ever, something like hell.
JOSEPH KIRSCHVINK: Looking at an active volcano you realise that
magma tens or hundreds of kilometres below the surface couldn't
care less whether there was a thin layer of ice over the oceans.
It will still emerge.
NARRATOR: Volcanoes survive ice ages because they have a direct
channel to the molten rock deep within the Earth, rock that reaches
temperatures of over 1,000 degrees, but that would only melt ice
in their immediate area. Kirschvink had spotted something else about
volcanoes: they also produce gas, ten billion tons a year. One gas
volcanoes emit in huge quantities is carbon dioxide, a gas that
causes the greenhouse effect and global warming. Today carbon dioxide
is being pumped into the atmosphere by both volcanoes and industrial
activity, but what stops the Earth from overheating is that we have
a natural way of removing the excess carbon dioxide from the atmosphere.
Rain is the Earth's natural cleaning agent. As it falls through
the atmosphere each droplet of rain absorbs carbon dioxide and cleans
the air, but Kirschvink realised that on a snowball Earth there
could have been no rain. The snowball was so cold all the water
on the planet's surface was frozen solid. Without liquid water nothing
could have evaporated into the air, so there would have been no
clouds and without clouds there can be no rain and without rain,
Kirschvink realised, there would have been nothing to cleanse the
atmosphere of carbon dioxide.
JOSEPH KIRSCHVINK: You can't have rain if you don't have evaporation,
so I couldn't see anything that would scrub out the carbon dioxide
from the atmosphere under those conditions.
NARRATOR: It meant there would have been nothing to stop the carbon
dioxide from the volcanoes from building up over millions of years.
It would have caused global warming on an inconceivable scale. Kirschvink
came across calculations showing that after ten million years without
rain the atmosphere would have been 10% carbon dioxide. Today it
is far less than 1%. This extra carbon dioxide would have created
a greenhouse effect that raised the temperature to an average of
50 degrees Centigrade, hotter than the Earth has ever been, hot
enough to melt the ice.
JOSEPH KIRSCHVINK: And that seemed to be a natural and possible
escape, certainly enough to break the snowball, the ice condition.
NARRATOR: Joe Kirschvink had cracked it. He had found the way out
of the runaway freeze, a way that made perfect scientific sense,
a way that was consistent with the laws of nature.
JOSEPH KIRSCHVINK: The realisation that we may have found the way
out of the snowball was wonderful.
NARRATOR: By 1990 Kirschvink had evidence that the tropics had frozen
over for ten million years and he'd come up with a theoretical escape
route from the runaway freeze, but the problem was it was just a
theory. He had no physical evidence to prove the ice had melted
because of an extreme greenhouse effect and without that evidence
the snowball Earth theory continued to be ignored. But all that
was about to change. In 1992 Paul Hoffman entered the story. One
of geology's most respected, but open-minded figures, he was to
turn into one of the snowball Earth theory's most fervent disciples.
PAUL HOFFMAN: I love the snowball Earth theory. I mean it's almost
a religious ferocity with which I want to get across this, this
saga of Earth history with so many twists and turns and, and events
that, that are, are, are so far outside the, our own experience.
NARRATOR: Hoffman's mission was to find that hard evidence that
had alluded Kirschvink, the final piece of the puzzle that would
prove the snowball had ended because of the greenhouse effect and
he knew just where to start looking: Namibia. Hoffman was drawn
to Namibia first by the drop stones, but even more by what sat immediately
on top of them. Towering directly above were huge formations called
cap carbonates, calcium carbonate crystallised into rock. These
bizarre structures seemed to appear right out of the blue.
PAUL HOFFMAN: Above this line right here... creates... on top no
more stones whatsoever, so the glaciation must have come to an abrupt
end and sitting directly on top is a thick pile of carbonate and
it's puzzled geologists for generations.
NARRATOR: What really puzzled geologists was that caps made from
calcium carbonate are usually formed in warm water, but in Namibia
they had suddenly appeared on top of an ice-cold glacier.
PAUL HOFFMAN: What this indicates is that you go from glacial conditions
to an ocean that is warm in a flash.
NARRATOR: To most geologists this instant change from cold to hot
rock defied their understanding, but Hoffman suspected it might
be a huge clue, that the sudden appearance of mountains of calcium
carbonate must somehow be linked to the death of the snowball in
a colossal greenhouse effect, but how? Hoffman needed someone who
could explain why calcium carbonate would be formed not just because
of warm conditions in general, but specifically in the conditions
created by a melting snowball Earth, so he turned to a geochemist,
PAUL HOFFMAN: I talked about this problem with a number of people
but the one person who grabbed this problem with both hands right
from the outset was my colleague, Dan Schrag.
NARRATOR: Painstakingly they analysed the snowball's theoretical
final moments stage by stage, working out what chemical and climatic
processes were at work. First they realised that as the ice melted
it would produce liquid water. The water would then evaporate and
create clouds and those clouds would cause a change in the weather
the likes of which has never been seen by human eyes.
DANIEL SCHRAG: When the ice is retreating this is probably the most
spectacular climate change in our history. In some ways we're going
from the coldest climate the Earth's ever experienced to the warmest
climate the Earth's ever experienced. We immediately said that this
was the mother of our climate changes.
NARRATOR: The most elemental powers of nature would be unleashed
upon the Earth.
PAUL HOFFMAN: One would predict hurricanes of such intensity that
our unimaginable, so it's quite possibly you could have had waves
of, you know, 100 metres in, in, in amplitude coming in and crashing
in on the shoreline, so it would just be unbelievably violent.
NARRATOR: And above all there would be rain, the first rain storms
for millions of years, rainstorms that would last at least a century
and it wouldn't be just any rain. The rainwater would react with
the vast quantities of carbon dioxide in the atmosphere and form
carbonic acid. This acid rain would then deluge the Earth. The acid
rain would pound the exposed rocks, producing a violent chemical
reaction. It would break the rocks down into their consistuent parts,
one of which was calcium. This would then fuse with the carbon in
the acid rain. The result: mountains of calcium carbonate exactly
as they could see right above the drop stones in Namibia.
DANIEL SCHRAG: Suddenly it became clear that the natural expectation
of a prolonged global glaciation ending in extremely high levels
of carbon dioxide was that you would expect these very unusual thick
carbonate rocks should immediately follow the glacial deposits.
NARRATOR: Hoffman and Schrag had found the final evidence.
PAUL HOFFMAN: The beauty of the snowball Earth theory is exactly
that it links the chemistry, the geology, the planetary science
and bam-bam-bam, all of the facts are, are consistent with the predictions
of the theory.
NARRATOR: In 1998 Hoffman and Schrag made a triumphal tour of the
world's universities promoting the snowball theory, and then someone
threw a spanner in the works. An entire scientific discipline, the
biologists, took one look at the ten million year long snowball
Earth and said it was quite simply impossible. One scientist who
had problems with the snowball was Guy Narbonne. He, like many other
biologists, could see there was a fundamental problem reconciling
the snowball Earth theory with what he knew.
GUY NARBONNE: The geological evidence speaks very strongly of ice
sheets marching on the Equator. The biological evidence speaks very
strongly of open water being available at this whole time.
NARRATOR: Narbonne's problem was another set of nature's laws, nothing
less than the laws that govern life itself. 600 million years ago,
when the snowball was said to have struck, there was nothing living
on the land. It all existed in the sea, and it was not life as we
know it. The most common organism on the planet was this: cyano-bacteria.
This mass of fossilised cyano-bacteria is so ancient it predates
even the snowball.
GUY NARBONNE The oldest fossils that we have in the world are stromatalytes
and these are colonies like you see here and they're made out of
literally billions of cyano-bacteria.
NARRATOR: What made cyano-bacteria and more sophisticated ancient
organisms like green algae central to the snowball debate was that
they photosynthesised. Just like plants today under the water these
life forms absorbed sunlight and converted it into energy, so these
species' chances of surviving the snowball would have depended on
whether there was enough sunlight for photosynthesis in the snowball
seas at a time when every inch of the planet was allegedly covered
in thick ice.
GUY NARBONNE: Light penetration through ice is not great if the
ice is more than a couple of tens of metres thick.
NARRATOR: And that was the problem biologists pointed to in Hoffman
and Schrag's work. Their calculations had reckoned on the snowball
producing ice sheets up to a kilometre thick and even in the warmest
places around the Equator they would have been tens of metres thick,
more than enough, biologists believe, to block out any sunlight
from the oceans and that meant death to most things that depended
on photosynthesis for life.
GUY NARBONNE: You cut off photosynthesis and within a few years,
let alone a few million years, mass extinction.
NARRATOR: It meant that many of the photosynthesising species should
have become extinct 600 million years ago and the trouble was they
hadn't. Cyano-bacteria grow in rock-like colonies all over the tropics
today, as do other photosynthetic plants dating from before the
snowball like green algae. For many biologists there seemed to be
only one possible conclusion: there may have been a severe ice age,
but not a fully fledged snowball that covered all the oceans because
life forms that should have died out are still with us. Unless someone
could find a way for marine life to survive under a thick sheet
of ice the whole theory would be back in the bin. Then along came
the man from NASA, Chris McKay.
DR. CHRIS McKAY (Space Science Division, NASA): I'm a planetary scientist with an interest in life in extreme environments, in particular environments that are cold and dry. Several years ago I saw the
papers about the snowball Earth indicating the geological evidence
that the Earth was ice-covered and had been ice-covered for millions
of years, plus the evidence that there were organisms, bacteria
and green algae, that survived this ice-covered state and that's
the puzzle: how could these photosynthetic organisms survive?
NARRATOR: McKay was intrigued because it just so happened he had
visited a place on Earth today that was so cold it could actually
be compared with the snowball of 600 million years ago: Antarctica,
the coldest place on Earth. Here temperatures can fall to -30%ordm;C,
almost as severe as the snowball at its warmest point (the Equator)
and deep in Antarctica are the dry valleys where there are lakes
smothered by an ice sheet many metres thick.
CHRIS McKAY: We think these little lakes represent a good model
for looking at the snowball Earth - could there by life underneath
the ice cover on a snowball Earth?
NARRATOR: Scientists were eager to discover if there was enough
light for life to survive in the water below the thick ice. They
were about to be astonished. There was light, lots of it, even though
overhead the ice was five metres thick. There was so much light
the water was filled with plant life and bacteria including two
organisms dating from the time of the snowball that would have needed
sunlight to live.
CHRIS McKAY: When we're diving in the lakes and swimming around
there's life in the water, there's bacteria, cyano-bacteria, but
there's also green algae.
NARRATOR: And McKay had a hunch as to why this photosynthetic life
could survive. It was something about the nature of the ice itself.
It was like glass. It didn't block out sunlight at all.
CHRIS McKAY: The transparency of this ice is very high and it's
due to the fact that it's freezing very slowly underneath this thick
ice cover. Now let's imagine the snowball Earth where there's also
a thick ice cover. The ice on the bottom is freezing very slowly
as well, yet you have the same optical properties as this clear,
NARRATOR: By freezing slowly, water rejects impurities such as salt
or dirt which make it cloudy, so the ice becomes clean and transparent.
Because of this transparency life-giving sunlight would have been
reaching down into the snowball seas. McKay realised that even at
its height there would have been havens around the snowball's Equator
where the ice was thin enough for photosynthetic life to cling on
below. But there was more. Although disciples of the theory accept
the snowball would have been death to most things, they argue whatever
life did survive would have emerged into a new world almost devoid
of competition, the perfect conditions for an explosion of evolutionary
change. These fossils show the new species which appeared soon after
the time of the snowball. All display a massive increase in size
and complexity from the simple organisms that lived before. These
are the first multi-cellular life forms. Even those with some questions
about the snowball theory recognise a new climate after a mass extinction
could be a spur for evolution.
GUY NARBONNE: All we can say for sure is that the complexity of
life dramatically increases after the snowball glaciations. What
we can infer is that the greatest environmental catastrophe to ever
strike the Earth is probably in some way related to the greatest
evolutionary explosions that have ever characterised the Earth.
NARRATOR: It may just be that the snowball saga was the biggest
force for the development of life the world has ever seen. But if
the snowball can change the course of life on the planet there remains
one final question. No one knows why the snowball happened or if
it could happen again. The sun is hotter than it was 600 million
years ago and is getting hotter all the time. Climate trends would
have to change dramatically. If it ever did happen again it almost
certainly wouldn't be for millions of years, but if it ever did
that would mean death to almost everything, including us.
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