Brief History, Destructive Impact: Geologists Debate 'Human Epoch'

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by
The Independent/UK

Brief History, Destructive Impact: Geologists Debate 'Human Epoch'

Mankind Leaves Mark on the Planet with the End of the 12,000-Year Holocene Age

by
Steve Connor

Biologists have their principles of evolution, physicists have their laws of thermodynamics and chemists have their periodic table.
For geologists, perhaps the most hallowed reference source is the
Geological Time Scale, a complex timeline depicting the entire history
of the Earth as a series of distinct periods, epochs and ages, from the
birth of the planet 4.7 billion years ago to the present day.

The
Geological Time Scale is quite literally set in stone. As geologists
dig down through the different sedimentary layers of rock, they go back
in time to periods when prehistoric humans with stone tools hunted
mammoths, to an earlier time 100 million years ago when dinosaurs
roamed the land, and even to a distant era 3.8 billion years ago when
life first arose in the ancient oceans of a more primitive world.

Changes to the Geological Time Scale resulted from natural events, whether it was the mass extinction of life from a giant asteroid
impact, or an ice age resulting from changes to the orbit of the Earth
around the Sun. Now, however, geologists are about to consider whether
humans themselves have started to influence the geological history of
the world.

They cite human-induced changes to the geology of
the Earth in support of such an almost heretical position, pointing to
alterations in the landscape caused by the growth of global agriculture,
the mass extinction of animals and plants caused by hunting and habitat
loss, differences in the composition of the atmosphere resulting from
the burning of fossil fuels, and to a corresponding change to the
global climate, including rising sea levels and increasing ocean acidity.

On
the immense scales of geology, time is measured in tens of thousands,
and indeed hundreds of millions of years. By comparison, human life and
history are imperceptibly short.

So it is
almost inconceivable that the Geological Time Scale should be changed
to accommodate the effect that such short-lived human activity has had
on the long history of the planet. Yet a significant number of
scientists believes there is now a strong case to justify the
modification of the Geological Time Scale to take into account the
impact of humans on the Earth.

They believe
that the current geological epoch, called the Holocene, which has
existed since the end of the last ice age some 12,000 years ago, should
now be amended. They suggest that the Geological Time Scale should be
formally changed to include the start of a new phase called the
Anthropocene, meaning the "human epoch".

Next
month the International Commission on Stratigraphy (ICS), the body
responsible for guarding the integrity of the Geological Time Scale,
will meet in Prague where it will receive a preliminary report from its
Anthropocene Working Group, a collection of experts charged with the
task of considering the case of introducing the new, man-made
sub-division. It will be the start of a long process that began in 2008
when the Stratigraphy Commission of the Geological Society of London
decided that there "was merit" to the idea of formalising the term.
But, ultimately, it will be for the disinguished members of the ICS to
decide the matter years of heated debate.

To
gauge opinion among the 50 or so members of ICS, The Independent
conducted a straw poll by email asking whether or not these experts
believed there was a strong case for making the Anthropocene into a new
formal division of the Geological Time Scale - and why. We received
just over 20 replies and nearly half of them - nine - agreed that the
case was already strong enough to consider the Anthropocene as a new
division. Most of them believed it should be classified as a new
"epoch", the same classification as the Holocene, which is a
subdivision of the Quaternary Period, the most recent of the three
periods of the Cenozoic Era.

"There is no doubt
the fingerprints of the Industrial Revolution will be clearly marked by
distinctive changes in the planet's biotas and environments in the geological record," said David Harper, professor of palaetontology at the University of Copenhagen in Denmark.

Mark
Hounslow of Lancaster University, and member of the ICS, agreed:
"Wherever future generations look back, be it in climate change, in
ice-sediment, or changes to the character of sediments... it will
appear to be a dramatic juncture of earth history."

Jan
Zalasiewicz, a geologist at Leicester University and chairman of the
Anthropocene Working Group, said the case for considering the
Anthropocene rests on the changes to biodiveristy, caused by habitat
loss and the introduction of invasive species, which is amplified by
global warming and ocean acidification. "Such changes leave permanent
markers, in the future fossil record in this case," he explained.

Barry
Richards of the Geological Survey of Canada agreed: "Human activities,
particularly since the onset of the industrial revolution, are clearly
having a major impact on the Earth. We are leaving a clear and unique
record... in the stratigraphic record."

A small
majority of ICS members disagreed, arguing it is far too early to
decide whether humans will leave a permanent, geological legacy.
Possibly, in some tens of thousand of years from now such a division
will be justified, said Professor Jozsef Palfy, head of palaeontology
and geology at the Hungarian Natural History Museum in Budapest. "Its
signature stratrigraphic record is such a thin veneer just now, that it
is not justifiable to distinguish it as a time-rock unit. The
Anthropocene is a nice and useful informal term, but I see no need for
its formalisation," he said.

Professor Jim
Gehling, a senior palaeontologist at the South Australia Museum in
Adelaide and another member of the ICS, said the present epoch, the
Holocene, began 11,700 years ago and coincided with agriculture, the
domestication of animals and crop plants, and the rise of urban
settlements. "This is effectively what I understand as the concept of
the 'Anthropocene', when humans began the processes that, more
recently, seem to be affecting climate change. The onset of the
industrial revolution is not particularly significant compared with the
shift from nomadic to agricultural lifestyles, and the consequent clearing of woodlands, draining of swamps and burning of fuel."

But
this is not what an increasing number of geologists believe. Professor
Sha Jingeng of the Chinese Academy of Sciences said the appearance of
humans on Earth was the greatest "bioevent" in geological history:
"That is why the Anthropocene must be used in the Geological Time
Scale."

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