The Solar System-6.
Spanning the floor of the city around the vents are carpets of yellow bacteria.
They form the foundations of the ecosystem that flourishes there.
Tiny shrimp like creatures called amphipods feed directly on the bacteria.
Larger organisms visit the city from the shallows, creating a complex food chain,
that supports a web of animals from snails and crabs to tube worms and octopuses.
Tube worms play an important role in the ecology of these environments.
These strange creatures can grow up to 2.5 metres long and live kilometres beneath the ocean.
They have well developed nervous system.
Their circulatory system uses complex haemoglobin, similar to the ones in our blood,
to transport oxygen around their bodies.
This creates the striking red plumes from the tip of the worms to their base.
They have no mouth or digestive tract.
They absorb nutrients directly into their tissues through a symbiotic relationship,
with the bacteria that lives within them.
Over half the body weight of a tube worm is bacteria.
This biological marriage is consummated by the exchange of molecules,
that are essential for each of these organisms to survive.
It is a relationship dependent on a chemical that is abundant around all hydrothermal vents,
and is essential to allow this ecosystem to survive.
Hydrogen sulphide, which smells of rotten eggs, is produced when sea water comes into contact,
with sulphate in the rocks below the ocean floor.
The bacteria living around these vents have evolved to use this molecule instead of sunlight,
as their energy source in a process known as chemosynthesis.
Reacting hydrogen sulphide with carbon dioxide and oxygen,
these unique bacteria create organic molecules, that all other organisms around them can feed off.
They also produce solid globules of sulphur that gives the ocean its vivid yellow colour.
The oxygen, carbon dioxide and hydrogen sulphide are delivered to the bacteria,
by the tube worm’s extraordinary circulatory systems.
The red plume filters these chemicals from the seawater,
then the blood transports them to the mass of bacteria in the worm’s bodies.
The bacteria then provide the organic compounds which are food for the worm’s.
This extraordinary relationship reveals the sheer adaptability of life,
in the most unlikely of environments.
These biological renegades have found a completely novel way of bioforming without sunlight.
The fascinating thing about finding this form of life, is that the conditions on the deep ocean floor,
are more similar in many ways to the conditions on worlds,
hundreds of millions of kilometres away in the Solar System,
then they are to the conditions just 2 kilometres above on Earth’s surface.
If life can not only survive but flourish in these conditions,
then it is reasonable to speculate that life might survive and flourish out there in the Solar System,
if similar conditions are present.
Life is a difficult thing to define.
One of the simplest definitions, is that life is a self sustained system,
capable of undergoing Darwinian evolution.
Reduced to the most basic building blocks, life is nothing more than chemistry.
First, you need the right chemistry set.
A human is made up of about 40 elements.
96% of humans are made of only four elements, carbon, nitrogen, oxygen and hydrogen.
Secondly, you need an energy source: a battery that generates a flow of electrons,
to power the processes of life.
Here on Earth, most of the life uses the power of the Sun.
Around the hydrothermal vents on the ocean floor, sunlight is not essential.
Energy can be harvested, for example,
from the chemosynthesis of hydrogen sulphide liberating the binding energy stored within molecules.
Thirdly, and seemingly universally, you need a medium through which the chemical process of life,
can play themselves out.
On Earth the solvent of life is water.
The Atacama desert is widely considered to be the driest desert in the world.
There are river valleys here that have been dry for 120,000 years.
There are rocks that haven’t seen rainfall for 20 million years.
Scientists have searched for bacteria, the most basic form of life, in the Atacama,
and they have found absolutely nothing.
It is the starkest evidence that even the most primitive form of life, means water to survive.
This seemingly fundamental link between water and life,
is driving the search for life in the Solar System.
Earth is the only planet that has standing liquid water on its surface.
In planets too close to the Sun, and too hot like Venus, the water is evaporated long ago.
In Mars the only surface water is locked in polar ice caps.
Many of the moons around the gas giants, and even the rings of Saturn,
are made of large quantities of water.
However in the depths of space, it is frozen into solid ice.
Water may be hiding below the surface of a moon or planet.
It is also possible that liquid water once flowed across the surface of some planets,
at some point in Solar System’s history.
If it did it should be able to find the evidence, because wherever water goes it leaves its footprint.
A normal river valley leaves behind a characteristic V shaped cross section,
that is replicated in river systems across the globe.
The other commonly observed effect of water are U shaped valleys carved by glaciers.
The Scablands are a unique geological formation,
that stretch across a vast area of the state of Washington.
They demonstrate on a spectacular scale how water can carve its signature into rock.
The valleys of Scablands have a rectangular cross section.
When first studied, this could not be explained by any known geological phenomena.
Later, geologists concluded that the unique geometric erosion patterns of the Scablands,
was caused by a vast quantity of water, hundreds of cubic kilometres in volume,
passing through the area in a short period of time.
It was revealed that the unique features of the landscape bear witness,
to the largest flood the Earth has ever seen.
Between 13,000 and 15,000 years ago, at the end of the last Ice age, a huge glacier lake,
known as lake Missoula, lay 320 kilometres to the east of the Scablands.
It was held in place by a vast wall of ice.
It was a dam that held back millions of cubic metres of water,
for thousands of years during the ice age.
As the water levels increased behind the dam, the ice wall was put under more and more strain,
until eventually it failed.
When it ruptured, over 2,000 cubic kilometres of water swept out in a single catastrophic event.
The flood waters were at least a kilometre deep, travelling at 130 kilometres an hour.
The energy released was equivalent to 4,500 megatonnes of TNT.
As the flood waters tore across the landscape, they carved out a 30 kilometre long canyon.
This was the largest waterfall the world had ever known.
This flood was 10 times larger than all the rivers in the world put together.
Current estimates suggest that this vast and complex landscape was created in a week or less.
The Scablands reveal one of the characteristics signatures that water can carve into a landscape.
We must be able to look for similar evidence of water’s mighty work on the surfaces of other worlds.
For over a century, Mars has been held up as a prime candidate on which alien life might be found.
We are still searching diligently for the tell-tale signs of waterways on Mars.
Images taken by the Mars exploration rover Opportunity, in 2004,
reveal that Mars has features cut into its surface, that is almost identical to those in the scam lands.
This suggests that similar huge floods might have torn across the surface of the planet.
This implies that vast amounts of water rapidly flowed over the surface of Mars,
at some point in the past.
This alone does not point to the existence of the conditions require for life.
The floods that created the landscapes in Mars may have lasted only for a few days.
For life to get a foothold we need standing water, lakes and rivers that persists for millions of years.
Robotic explorers are now looking for such evidence in the surface of Mars.
The Opportunity rover while examining a impact feature call the Endurance crater,
detected deposits of a remarkable mineral: gypsum.
This is a very soft mineral that has been discovered in large deposits on the surface of Mars.
Gypsum can be harvested from seawater.
The discovery of gypsum in Mars tells us something fundamental about the story of water in Mars.
The chemical formula of gypsum is calcium sulphate dihydrate.
The dihydrate refers to the two molecules bonded closely to the calcium sulphate.
This requires calcium and sulphate ions to be in the presence of liquid water for long periods of time.
With large deposits of gypsum found at multiple locations across the surface of Mars,
we can conclude that there must have been standing water on Mars at some point.
This suggests that the factors needed for life existed at some point in Martian history.
Mars was once a warmer and wetter planet.
It was a planet with oceans and floods, vast areas of standing water,
and hydrological cycle of a familiar Earth-like landscape.
The liquid water has long since disappeared from its surface.
About 3 billion years ago, Mars died as a planet.
Its core froze and the volcanoes that had produced its atmosphere seized up.
The solar winds then stripped away the rest of the atmosphere.
Any liquid water left would have evaporated or soaked into the soil, where it froze.
This left the surface of Mars too cold, too exposed, and too dry to support life.
We don’t know for sure whether life existed on Mars.
In 2007, the Mars Odyssey spacecraft discovered 7 strange circles,
on the Martian volcano, Arsia Mons.
Scientists deployed Odyssey’s infrared cameras to record the temperature swing,
of the holes across a series of Martian days.
Surprisingly the temperature change from day to night in these holes,
were much less than the change in the surrounding area.
Such stable temperatures are seen in caves on Earth.
Caves on Earth maintained a constant temperature.
The deeper they are, the more they can resist the effect of the passing Sun outside.
This is why many life forms use caves as shelter on Earth.
NASA scientists call these holes as seven sisters.
These holes open up another front in the search for life on Mars.
There is a possibility that some caves could have protected life from the hostile environment outside.
The conditions may not be perfect for life to exists,
but our experience shows that all living things are not so fussy.
The Cueva de Villa Luz, a cave in Mexico,
is a good example of a hostile environment to a human being.
It is full of hydrogen sulphide gas, pumped into the cavern rich in this corrosive gas.
The gas dissolves in water to produce sulphuric acid,
that has eaten its way through the limestone rock to create the cave system.
It is incredibly toxic to humans.
However, the cave is teeming with life.
There is a type of fish which has adapted to tolerate these conditions.
They have large quantities of haemoglobin in their blood that allows them to move around,
using the sparse quantities of available oxygen in the water.
Deeper in this toxic cave, is a profoundly interesting organism, called snottites.
This life form derives its energy not from the Sun, but from noxious gases around it.
These tiny creatures use hydrogen sulphide to drive their metabolism.
They react hydrogen sulphide with oxygen to produce sulphuric acid.
They breathe in hydrogen sulphide and oxygen to produce sulphuric acid.
The highly concentrated sulphuric acid has a pH of almost zero, and is highly corrosive.
Such creatures exist just below the surface of our planet.
Organisms that can extract energy from the minerals around them, are found under the ground,
all over the world.
In fact, this way of life is so successful that it is thought,
that there may be more life mass living beneath the Earth’s surface, then there is on it.
This raises a intriguing possibility.
Why can’t such organisms survive and flourish beneath the surface of mass.
Living below the surface in Mars is a good idea, because the surface is incredibly hostile.
Any form of life on the Martian surface will be subjected to ultraviolet radiation from the Sun.
Mars is also very cold place,
and the atmospheric pressure doesn’t allow water to exists on the surface.
There seems to be one tantalising clue,
that suggests that there might be something below the Martian surface.
In 1768, the scientist Alexander Volta was still 30 years away, from inventing the first battery.
He collected gases from the Marshes around his home in Italy.
One of the gases he collected and studied was methane, or CH4.
Volta demonstrated that methane could be ignited with a electric spark.
Today we use methane as one of our main sources of fuel,
because methane is the main component of natural gas.
Its abundance makes it widely available and relatively cheap.
The deposits of methane under the Earth’s surface are generated by the decay of organic material.
They are often linked to sites containing other fossil fuels.
Methane is also present in our atmosphere.
Termites are unusual organisms who eat dead organic matter.
There primary diet is wood.
There are many species of these insects.
In the process of digesting wood, they produce vast quantities of methane.
They pump an estimated 50 million tonnes of it into the Earth’s atmosphere.
There is a lot of methane in our atmosphere, produced either biologically or by geological processes,
such as mud volcanoes.
Surprisingly methane has been detected in the atmosphere of Mars,
a planet we thought as both geologically and biologically dead.
There is no geological process that could produce and sustain the levels of methane,
we observe in the Martian atmosphere.
In 2009, Scientists at the Keck observatory,
announced that they have discovered substantial pockets of methane on the surface of Mars.
In the warmer summer months, thousands of tonnes of the gas are released from vents on its surface.
This can only mean one of two things.
The methane plumes are emanating from previously unknown geological processes.
This would mean that Mars is a geologically active planet.
The other option is that the methane is being produced from a biological source,
just like termites on Earth.
The interesting thing about termites, is the way they digest wood.
They use symbiotic micro organisms called Archaea, which live in their guts,
to do the methane producing work for them.
Archaea used to be thought of as an unusual group of bacteria.
We now know that these basic living units are in fact a completely distinct branch of life.
Along with bacteria, and the more complex cellular units called Eukaryotes,
Archaea are one of the three separate branches of life on Earth.
They are found all over our planet.
They fill the soil, the oceans and the guts of humans, cows and termites.
They are also the most common organisms found beneath the surface of Earth.
Archaea thrive in many of the Earth’s most extreme environments.
The snottites in the Cueva de Villa Luz are members of the Archaea.
So are many of the micro organisms found living around deep sea hydrothermal vents,
producing millions of tons of methane which is pumped into the atmosphere.
This raises the possibility that the methane we see in Mars might be produced by organisms,
living below the Martian surface.
Mars is not the only place in the Solar System that we think could harbour alien life.
The far flung reaches of the outer Solar System provide a plentiful source of water.
Half a billion kilometres away from the Sun, water can be expected to be frozen as hard as steel.
Jupiter, the gas giant, is surrounded by 63 moons.
Many of them contain vast amounts of ice.
Callisto is the most distant of Jupiter’s moons.
It orbits at a distance of 2 million kilometres from Jupiter.
It takes 16.7 days to complete an orbit, and the same amount of time to turn on its axis.
About half of it is made up of water ice.
The ice is frozen as hard as steel on its surface, at a temperature of minus 155 degrees Celsius.
Ganymede the moon of Jupiter, is the largest moon in the Solar System.
With a diameter of 5200 kilometres, this moon is larger than the planet Mercury.
It is composed of silicate rock and ice.
It surface temperature is minus 160 degrees.
The freezing temperatures on these moons, locked up in thick ice, seems far too hostile to support life.
But looks can be deceiving.
The Jupiter’s moon Europa, is about the same size as our moon.
It orbits at a distance of 671,000 kilometres.
It has a tenuous atmosphere composed of some oxygen.
Europa has the smoothest body in the Solar System.
It surface is made of an unbroken shell of ice, at a temperature of minus 160 degrees.
Beneath its thick layer of ice, Europa holds an astonishing secret.
Images of it reveals deep cracks that criss cross the surface of Europa.
There are areas where ice has been broken into icebergs and jumbled up before refreezing.
When we compare this to the image of sea ice on Earth, a similarity becomes apparent.
They are caused by the movements of the oceans under the ice, that make it bend and crack.
This suggests that something similar is happening in Europa.
There must be liquid water, and ocean, under Europa’s icy shell.
The Galileo probe took high quality images in the 1990’s.
They are being studied by scientists for additional evidence,
for the theory of subterranean ocean on Europa.
Europa orbits around Jupiter, in a slightly eccentric orbit.
The slight eccentricity of the orbit is maintained by the gravitational interaction,
with its neighbouring moons, Io and Ganymede.
Just as for the volcanic moon Io, the effect of the eccentric orbit on Europa is profound.
Europa is stretched and squashed as it moves close to and further away from Jupiter.
This causes the interior of the moon to heat up by friction.
This melts the frozen ice to produce a subterranean ocean.
Europa, like many other moons in the Solar System, including our own,
is tidally locked to its parent planet.
It always keeps the same face pointing towards Jupiter.
Scientists have found that Europa’s surface is rotating at a different rate to its interior.
Measurements of Europa’s magnetic field, and its interaction with the powerful magnetic field of Jupiter, suggests that is ocean may be salt water, 100 kilometres deep.
This means that there is twice as much life giving liquid water, than all the Earth’s oceans combined.
In principle life could exist in the oceans of Europa.
It could be similar to the life we find around the hydro thermal vents, in the oceans of Earth.
It is a tantalising case, for being the most likely habitable environment in our Solar System.
The spectacular ice caves in the Vatnajokull glacier, in Iceland,
are a beautiful demonstration of how the laws of physics can create an awe inspiring cathedral of ice.
The cave tunnels into the heart of the glacier, where ice has been frozen for thousand years.
The walls of the cave tell the story of the eruptions of Iceland’s many volcanoes,
over the millennia it took for the glacier to form.
Scientists have been looking for signs of life, in these caves.
For a long time it was thought that microorganisms found here,
can be present only in a state of deep antibiosis - suspended animation.
It is now becoming clear that some microorganisms are actually actively living in the ice.
Under a microscope one can clearly see living bacteria, taken from samples in the ice.
Some microorganisms are capable of causing the ice to melt,
because they generate essential anti freeze proteins.
They change the temperature at which ice goes from solid to liquid state.
They form little pockets of liquid water, a few microns in diameter.
This is like a ocean for the bacteria, in the frozen glacier.
This suggests that similar microorganisms could exist in Europa.
There are mysterious red stains in Europa.
They are similar to the colours of cyanobacteria found on Earth.
This leads to speculation that microorganisms could be present in Europa.
It is only on Earth that the temperatures and atmospheric pressure,
are just right to allow oceans of liquid water to exists on the surface of the planet.
Earth is big enough to have retained its molten core, that not only powers the geysers and volcanoes,
but also produces our magnetic field that fends off the solar wind,
and protects our thick nurturing atmosphere.
It is a combination of all these factors, that have been stable for long enough,
for life to evolve into magnificent complexity on Earth.
Life on Earth today is the result of hundreds of millions of years of stability.
This has given the time to evolve complex organisms like human beings on Earth.
The rarest combination of chance and the laws of nature, have created our civilisation.
Our civilisation is the wonder of the Solar System.