Frequently you’ll hear, on the news, on
social media, about the troubles that the environment is facing. The “very
sustainability of our fragile blue-green planet,” they say, is threatened. That
has always seemed quite unlikely to me – after all just how ‘fragile’ is this
planet we find ourselves on? Because it has endured quite a lot throughout its
4.5-billion-year lifetime, and yet…
It took life 700 million years to appear on
planet Earth, and these basic forms of life were quite resilient. It took until
450 million years ago for an event to occur that could threaten it. It was the
start of the Ordovician-Silurian extinction event, lasting for 25 million
years. A burst of volcanic activity occurred, depositing silicate rocks on the
surface of the earth – silicate rocks that drew carbon dioxide from the air as
they eroded. At the time, the earth was a veritable greenhouse, with a thick
atmosphere of carbon dioxide that trapped heat from the sun. As the carbon
dioxide was leeched from the air, heat could escape, and the atmosphere
changed. The planet cooled. At the poles, ice caps started to form.
With glaciers starting to form, sea levels
dropped, and the habitat of sea life was extinguished. But glaciers break up, and
then drift back into the ocean – and as a result, melt and cause sea levels to
rise again. With sea levels rising and falling, populations moved into areas,
just to go extinct when the next wave of glaciers built up and lowered them
again. During this 25 million years, this cycle repeated 5 times. 85% of marine
species went extinct, and those that survived found a different environment to
flourish in once sea levels stabilised.
By 375 million years ago, the land had been
colonised by plants and insects had evolved. Life was flourishing once again, but
life does not commonly have a global view, instead focusing on survival.
Plants, now growing without the intense competition of previous ages, could
grow much larger, increasing in size from 30cm to 30m, and developed seeds,
allowing them to spread much further. They developed massive root systems,
entrenching themselves in the soil, and splitting it up, eroding it. This
released a large amount of nutrients into the water, causing eutrophication –
the wild growth of plants and algae. Unfortunately, that results in the water
being depleted of oxygen – or anoxia.
Anoxia in the water resulted in the mass
extinction of vertebrate species, with 97% disappearing. This Late Devonian
extinction event, as it is termed, devastated marine habitats and sharks, for
example, only survived as a species less than a meter long. It would take 40
million years for them to increase in size again. And yet after this 15 million
years long extinction event, the continents were green, and land life started
to make gains.
Then, 252 million years ago, less than a
hundred million years later, a global disaster occurred. An asteroid impacted
the earth at Araguainha in Brazil. The impact occurred in oil shale, releasing
massive amounts of oil and gas. Massive earthquakes were triggered, releasing
buried coal. This mixture of oil, gas and coal precipitated global fires. The
world burned. Global warming was the result, and with layers of ash on the
oceans, anoxia occurred once again. This allowed sulphate-reducing bacteria to
thrive, producing large amounts of hydrogen sulphide. This poisoned the plants
on the surface, and depleted the ozone layer, allowing fatal levels of UV
radiation to kill much of the life that was left.
96% of all marine species went extinct in
this Permian-Triassic extinction event. Over 70% of vertebrate species went
extinct, and this was the only known mass extinction of insects. So much
biodiversity was lost, that it took life 10 million years to recover. In their
wake, reptiles and eventually dinosaurs began to emerge. But it would take the
Triassic-Jurassic extinction event that occurred 202 million years ago to make
dinosaurs the dominant form of life on the planet. Not much is known about this
extinction event, since it happened in such a short time-frame – less than 10
000 years. It caused the extinction of around half of all known species.
Then, after the universe took a break for a
bit, it happened again. 66 Million years ago, an asteroid struck Central
America, near the Yucatán peninsula, in what is today known as the Chicxulub
crater. This 10 to 15 km rock impacted with the force of 100 teratonnes of TNT
– a billion times more powerful than the atomic bombings of Hiroshima and
Nagasaki. The Cretaceous–Paleogene extinction event had begun. Global
firestorms resulted from the heat pulse – the entire terrestrial biosphere
burned. The dust cloud blocked sunlight for a year, killing all
photosynthesizing plants. The oceans became acidic, killing all shelled
organisms. Over the next 10 years, the dinosaurs died out, along with 75% of
all species. But a new form of life emerged – mammals.
Then, 200 000 years ago, a new species of
mammal emerged – homo sapiens sapiens. This species was remarkably adept at
bending its environment to suit it, instead of adapting to suit its
environment. There appeared the first faint glimmers of intelligence. The
fruits of intelligence were many: fire, tools and weapons. The hunt, farming
and the sharing of food. Families developed, then the village, then the tribe,
until finally this species developed civilisation. Then, 200 years ago, they
developed industrialisation. Soon, the riches below the earth were to be used
as fuel – carbon deposits such as coal, and oil, were burned to power their
burgeoning civilisation. But like life in the first few extinction events, this
species did not have a global view, and focused only on its own survival. A
controlled global fire was underway, and similar to the previous extinction
events, changes started to occur. Two weeks ago, they finally increased the
carbon dioxide levels in the atmosphere back up over 400 parts per million –
for the foreseeable future. Within the next 50 years, this species will have
raised the global temperatures by 2°C, and the next extinction event will have
begun.
So you see, the blue-green planet isn’t
quite as fragile as everyone expects. Life, as Ian Malcolm was so fond of
saying, will find a way. The planet will do fine – it’s the people that are
doomed! As a result of our actions, Namibia has been experiencing the worst
drought in memory – and if we as a species cannot find a solution, it will be
the first of many. It would be quite sad if the monumental feats of our
civilisation are to be swallowed by the mists of time – I, for one, am quite
proud of what we have achieved. But if that is what should happen, I shall
sleep soundly, knowing that the planet has survived, as it always does. After
all, 99% of all species that have ever existed are now extinct. Maybe the next
intelligent species to emerge after 50 to 100 million years will do better. Or
maybe the dinosaurs will make a comeback. I can only dream…
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