20 April 2019 | NewScientist | 37Earth’s crust to create a low-lying subsiding
basin that filled with sediment: Mesopotamia.
The Harappan civilisation emerged along
the Indus valley at around the same time as
the Sumerians in Mesopotamia, and did so
in an essentially identical tectonic scene.
The Indus flows along the foreland basin that
sags down alongside the mighty Himalayas,
which were created by the crashing of India
into Eurasia. Active plate tectonics therefore
provided not only the cradle for the very
evolution of humanity in Africa, but also the
spawning points for our first civilisations.HOW WE ARE RISKING IT ALL
Today, the power dynamic between Earth
and humanity has flipped. Human-driven
climate change is the most severe jolt in
global temperatures in 55 million years.
That earlier climatic spasm was crucial to
the development of our early ancestors, but
a similar event today would have catastrophic
consequences for our present way of life.
The effects of global warming will be far
from uniformly distributed, and different
regions will experience opposite effects.
Many will see increasing droughts or the loss
of fertile land as deserts form, while others
will experience more intense bursts of rainfall
and flooding. Both these extremes threaten
to severely disrupt reliable agriculture.
Melting polar ice caps will raise sea levels and
risk inundating coastal areas and cities, while
the disappearance of mountain glaciers will
significantly affect water availability. All the
while, tropical diseases will reach further from
the equator, and intensifying heatwaves will
kill more vulnerable members of society.
Taken together, these factors will drive
widespread displacement of people and mass
migration. Left unchecked, human-driven
climate change will shape our future as much
as the planet itself has shaped our past. To
navigate it safely, we must understand the
deep connections that tie us to our planet,
and come to terms with how Earth made us. ■Lewis Dartnell is an astrobiology researcher at the
University of Westminster, UK, and author of Origins:
How the Earth made us (originsbook.com)“ Plate tectonics provided
the spawning points for
our first civilisations”Blue belt
A crescent of Democratic voters in the southern US reflects the unique geology of the ground they live on.
Rocks laid down during the Cretaceous period millions of years ago created soils perfect for cotton farming.
This resulted in the forced migration of slaves from Africa, whose descendants favour liberal politiciansMississippi
river
Cretaceous-
aged rocks2016 presidential election results Hillary Clinton (Democrat) Donald Trump (Republican)SOURCE: USGS.GOV; ORIGINS: HOW THE EARTH MADE USA geological legacy
THE INNER SEA
Throughout history, the
Mediterranean has buzzed
with a multitude of notable
cultures and civilisations.
Many flourished on its
northern shores – the Greek
islands or Italy – more so than
on the southern lip along the
African coastline. This may
be because the northern
Med has an intricate geometry
full of natural harbours and
islands, perfect for early
sea-faring societies, whereas
the coastline to the south
is mostly smooth and less
accommodating. This
fundamental difference is
due to continental drift:
Africa is being subducted
underneath the Eurasian
plate as it rides north,
crumpling up the European
coastline and leaving that of
Africa smoother.ISLAND NATION
The UK’s island status is a
defining part of its identity.
The natural moat that
surrounds it has protected
it from most invasions and
so maintained the balance
of power on the continent
by making it hard for any
one state to consolidate a
European empire. All the
while, its relative proximity
has allowed it to prosper
from trade. But Britain hasn’t
always been an island – it
used to be joined to France
by a land bridge. This physical
connection was eroded
away by a megaflood that
began almost half a million
years ago, as a glacial lake
rapidly drained away during
a previous cold spell. The
iconic white cliffs of Dover
are this land bridge’s
northern stumps.BEDROCK OF DEMOCRACY
The impact of the planet’s
geology is even visible in how
people vote. Running through
the staunchly Republican
south-eastern US states, for
example, is a distinct crescent
of Democrat-voting counties
(see “Blue belt”, below).
This curve closely follows an
exposed band of 75-million-
year-old rocks laid down
during the Cretaceous period.
These have produced a very
rich, fertile soil, which was
found to be perfect for
growing cotton. In the
mid-1800s, cultivation of this
crop led to a boom in slave
labour. A high proportion
of African-Americans still
remain in these areas, where
they favour the more liberal
policies of the Democratic
party, and continue to vote for
its presidential candidates.Lewis Dartnell will be speaking at
New Scientist Live in London
newscientistlive.com