This is Greenhead Moss’s story, but
it isn’t just about the bog or about the plants
that grew around it. The peat can also tell us about
our own history, long before written records: how
people used the land and transformed the area around
Wishaw from woodland to farmland and then to
industry.
You can see how this story relates to
the moss by visiting the stratigraphic stairway which
has been built up the south-western corner of the
bog, where open-cast mining has removed peat down to
the underlying bedrock. Each step tells you how old
the peat is at that level and this is the same as the
timeline to the left/right, which links the
environmental record on these web pages to the slowly
accumulating peat beneath your feet on Greenhead
Moss.
Stratigraphic
Stairway with dates on each step relating to
how old the peat is at that level
|
Plan
showing the route that the stratigraphic
stairway takes through the moss
|
Out of the Ice Age: the start of the
journey
We hear a lot about the Greenhouse
Effect and how the climate will change in the future.
This is caused by the way we are using the
earth’s resources now, but changes in the
Earth’s climate are nothing new. Ice cores are
especially good at recording changes in the
Earth’s climate over many thousands of years
because the ice traps gas bubbles and dust particles
in each annual layer of ice, so we can tell how the
Earth’s atmosphere has changed.
Evidence like this tells us that the
climate has been very variable throughout the history
of the planet, fluctuating between ice ages (glacial
periods) and warmer interglacial periods, each
lasting up to sevral hundred thousand years. But even
in each glacial or interglacial, the climate didn't
just stay the same - there were smaller fluctuations
in rainfall and temperature.
Each glacial and interglacial period has
a name to make it easier for scientists to discuss:
we are living in an interglacial called the Holocene.
The end of the last Ice Age and start of
the Holocene – about 11200 years ago - takes us
back to the time when Greenhead Moss started to form.
These last glaciers only came as far south as Loch
Lomond, having spread from Rannoch Moor, but areas
near the margin of the ice sheet were too cold for
trees to grow. Places like Glasgow and Wishaw were
covered by open low alpine scrub and tundra
vegetation which is made up of grasses and herbs like
dock and wormwood that are adapted to broken soils
because freezing makes the ground crack and buckle
unevenly. These types of plants are now found on high
mountains and north of the Arctic Circle.
Greenhead Moss wasn’t a bog then at
all: it was a lake lying in a depression in the
land’s surface.
At the start of the Holocene, the
climate began to warm quite quickly and the ice sheet
retreated northwards. Within 500 years, the climate
had warmed from mean January temeratures of -20oC and
mean July temperatures of less than 10oC to
conditions similar to the present day. Plants which
need warmer weather to grow began to migrate north
and all plants grew more abundantly in the warmer
conditions. As fragments of dead plants accumulated
in the lake underneath Greenhead Moss, it became
overgrown and was filled in by fen peat.
For more detail see ‘How
bogs form’
Things
were also changing on the dryland around the lake.
Soils were still adapting to the new climate and were
quite unstable, so the most common plants are ones
which we see now growing on disturbed waste ground,
like dock, nettles and grasses. There were some
patches of scrub – willows on wetter soils near
the lake and juniper on drier ground.
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