New Scientist - USA (2019-06-08)

(Antfer) #1
CHINA’S first farmers liked alcohol
so much they had two different
ways of making it.
Li Liu at Stanford University
in California and her colleagues
analysed the residues left on
pottery shards between 7000 and
8000 years old unearthed at two
early farming sites in north China.
At both locations, some of the

residues contained cereal starch
granules with signs of physical
damage similar to that caused
by fermentation.
A stumbling block when
brewing beer from cereals is to
break down their starches into
fermentable sugars. Significantly,
the ancient brewers at the two
sites appear to have used different
techniques to achieve this, say Liu
and her colleagues.
At Lingkou, tiny mineral particles
from plants, known as phytoliths,
were in the residues. This suggests

the brewers simply let the grains
sprout, which frees up the sugars.
But 300 kilometres to the west
at Guantaoyuan, the discovery
of a mix of phytoliths and fungi
suggests an alternative approach.

Here, the archaeologists say the
brewers triggered the breakdown
of starches by using a fermentation
starter made from mould (PNAS,
doi.org/c6rp).
Collectively, the evidence
suggests the history of these two
distinct fermentation techniques
stretches back to the early days
of farming in east Asia, says Liu.
“Alcohol would be used in feasting,
which helps some individuals to
gain high social status and to form
alliances,” she says. ❚

8 June 2019 | New Scientist | 9

THE Roman Empire lit so many
fires that the resulting air
pollution cooled Europe’s climate.
The finding adds to the evidence
that human societies have been
affecting Earth’s climate for
thousands of years, although
on a much smaller scale than
present-day global warming.
Complex societies can affect
the climate in many ways. People
burn fuel such as wood to heat
their homes, releasing soot and
greenhouse gases. They also cut
down forests to grow food, and
burn what remains once crops
are harvested.
Previous studies have estimated
the impacts past societies made
through releasing greenhouse
gases and converting forests to
farmland. A 2016 study concluded
that, in Europe and South-East
Asia, human-induced temperature
changes can be seen as early as
7000 years ago.
But these studies didn’t look into
the different ways that air pollution
affects climate, especially airborne
particles, or aerosols. Soot
particles from fires trap heat and
have a warming effect, while
particles of organic carbon scatter
sunlight and so do the opposite.

“We looked for the first time at
whether anthropogenic aerosols
had an impact on climate a long
time ago,” says Anina Gilgen of
ETH Zurich in Switzerland. She
and her colleagues estimated the
amount of pollution the Roman
Empire emitted, based on how
much land was used for farms,
homes and other purposes, and

then used this in a climate model.
Deforestation and other land
use changes led to warming of up
to 0.15°C. But the air pollution had
a cooling effect, causing an overall
temperature fall. Gilgen estimates
that Europe’s climate cooled by
0.17°C to 0.46°C, depending on the
true scale of the pollution (Climate
of the Past, doi.org/c6rs).
But Gilgen says the cooling was
probably too small to have a major
impact on Roman society. In fact,
at the height of the Roman Empire,

the European climate went
through a spell known as the
Roman Warm Period, which lasted
from about 250 BC to AD 400. The
cooling effect of the air pollution
may have slightly countered this
natural warming, says Gilgen.
However, the air pollution
from the fires may have been a
health problem for people in cities,

says Gilgen. The pollution might
also have affected rainfall because
water droplets condense around
aerosol particles, says Joy
Singarayer at the University
of Reading in the UK.
Other periods of Roman history
may have been affected by shifts
in climate. It has been suggested
that volcanic eruptions around
250 BC disrupted the African
monsoon, destabilising some
societies that the Romans were
then able to conquer. And rapid
climate shifts later on have been
linked to the collapse of the
Western Roman Empire between
AD 300 and 500. ❚

Roman air pollution caused


cooling across Europe


The Roman Empire
shaped climate as
well as culture

Old pottery
has revealed
how farmers
brewed
alcohol more
than 7000
years ago

Climate change

Colin Barras

Michael Marshall

HB

O/B

BC
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LI^ L

IU

0.46°C
Ancient pollution may have cooled
Europe’s climate by this much

Two ancient ways of


brewing beer found


by analysing old pots


Alcohol


What can we learn
from ancient tech?
newscientistlive.com
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