Interview with Dr Samantha Gibbs

What is ShapeShift?

The dimensions of the ShapeShift sculpture as it
spreads across the room are based on a record of
diversity along the Devon, Dorset and Isle of Wight
(IOW) coasts. This record has been collated using rock
samples stretching from the Triassic rocks at Lyme Regis
which are approximately 200 million years old through
to Paleogene rocks from White Cliff Bay (IOW) that
are 35 million years old. Diversity, or the number of
different species that were in existence at any given
time, dictates the width of the sculpture, and time runs
the length of the room with the oldest records to the
left as you enter through the front door.

The rock samples were collected in 1989 by a team
of UK micropaleontologists (scientists who study the
skeletal remains of past microscopic life) who made
a count of how many species of each of the major
microfossil groups were present in each sample*. The
surface of the sculpture is comprised of six materials
because six of these microfossil groups were found
along the coast. These are marine and freshwater
plankton species (calcareous nannoplankton,
foraminifera, dinoflagellates, freshwater algae) and
microscopic sea-floor species (shrimp-like creatures
called ostracods, sea-floor dwelling foraminifera).
The number of species in each of these microfossil
groups is represented by the width of each of the
horizontal bands of material that flow down the
length of the room. The combined width of these
bands – the overall width of the sculpture at any given
point – shows the total local diversity, i.e. the number
of species that lived in this area of the south coast at
each time interval. This local diversity is controlled by
a number of different factors, mainly environmental
conditions but also preservation and how many
species existed overall, i.e. global diversity.

What determines the height of the sculpture?

The height of the sculpture represents local
water depth. Water depth was the main factor
controlling local diversity during our study interval,
but temperature was also important, with diversity
generally increasing with increasing temperature. Local
water depth is controlled by a combination of global
sea-level effects, such as melting of ice-caps resulting
in sea-level rise, plus local controls such as how quickly
the seafloor and adjacent land is subsiding and how
much sediment is being added to the seafloor.
The height of the sculpture above the floor shows
how deep the water was at any given time – the
higher the sculpture the deeper the water. As you can
see, water depth along the south coast has varied
dramatically through geological time from deep shelf
seas of upwards of 50 metres depth, to rivers only a
few metres deep. The highest point – where you can
pass under the sculpture – is at Ballard Down. The
water depth here was around 150 metres 80 to 90
million years ago (referred to as Ma). The lowest point
along the sculpture – where you can walk across it – is
at Peveril Point and through to Swanage Bay, at about
125 to 145 Ma.

As a rule of thumb, microfossil diversity is lowest
where water depths are very shallow, such as lagoons,
rivers, estuaries etc, as these environments tend to
be relatively unstable with more variability in salinity,
muddiness, and food availability. Therefore, though
the relatively few species that find these conditions
favourable may exist in high numbers, the overall
diversity is low. Furthermore, diversity may also be
reduced because preservation of these organisms tends
to be poor in sandy, oxidized shallow waters or land
(terrestrial) conditions and therefore fewer organisms
are preserved. Conversely, local diversity is highest in
the warm shelf seas where marine conditions are more
stable and preservation is good.

What causes the changes mapped by the sculpture?

In general, the rocks of the Devon and Dorset coast
are younger from west to east. Therefore, as you walk
along the coast you are travelling through time and
through a pattern of diversity changes. For example,
walking east from Kimmeridge Bay we walk through a
sequence of environments that represent a fall in water
depth. By the time we are at Durlston Bay, waters
are so shallow that we are standing on a mixture of
terrestrial and lagoonal sediments. These have much
lower microfossil diversities than the deep water
Kimmeridge sediments. Continuing east through the
lower Cretaceous, very low microfossil diversities are
associated with the lake and river environments of the
Wealden Beds of Swanage Bay. Sea-level then began to
rise quickly and diversity with it. As we walk up to the
topographic high of the chalk at Ballard Down we are
also walking up to a peak in diversity and water depth.
Local and global microfossil diversity reached its all-time
high in these warm chalk seas of the upper Cretaceous
that covered much of Europe – not just because
species flourished in the stable marine conditions but
also because of the overriding evolutionary trend in
global diversities. This was prior to the massive collapse
in diversity associated with the extinctions of the
Cretaceous-Tertiary boundary at up to 65 Ma. At this
time up to 75% of fossil marine species, as well as a
large number of land plants and animals, disappeared
across a relatively short interval of time, with current
theories for the cause of these extinctions including
meteorite impact, sea-level fall and volcanic activity.

Why is there a gap in the sculpture?

Between approximately 80 and 55 Ma we have a 25
million year gap in our record, which includes the time
interval where the Cretaceous-Tertiary boundary should
be. These rocks are missing because there were large
sea-level changes at this time that caused both a lack
of sediments being laid down and also erosion and
removal of part of the sedimentary record. Therefore,
the chalk of Ballard Down abuts much younger rocks of
the Eocene to the east in Studland Bay and we do not
see the youngest Cretaceous or Paleocene rocks.
Is ShapeShift an accurate biodiversity picture?
We need to remember that this record only shows the
diversity of microscopic organisms that fossilise. This
means we are not recording real, total diversity, as we
are not representing the diversity of larger organisms.
Furthermore, many, perhaps most, animals and plants
never produce fossils because, for example, they do not
have hard skeletons or they live in an environment that
does not allow for good preservation. Fossil diversity
estimates will therefore always be lower than real
diversity. Though we are unable to truly quantify total
diversity, patterns of change in microfossil diversity
would in general mimic the overriding patterns we
would see if we were able to look at total diversity.
Despite these limitations, the diversity patterns
shown in the sculpture highlight the importance of
environmental change on local diversity, and the
superimposed influences of preservation and evolution
on the fossil record.

Why collaborate with an artist to present this
research as a sculpture?

As a scientist, I think it’s too easy to remain within
the confines of scientific language and within the
relatively small communication circles of academia.
We regularly present our research at national and
international meetings and publish in scientific journals,
but communication with the general public is rather
limited and often unimaginative. To be involved in
this project has meant a number of things to me both
professionally and personally.
Professionally, it allows me to address the societal
obligation we have as scientists to communicate to
the general public. This overlaps with the personal
aspects of this project: I get to spend lots of time out
of the office in a beautiful place and share with people
something of the amazing geological story of the rocks
under our feet. Also, with this unique integration of
geological data and art, I’m seeing geological data
in a whole new light. It’s difficult to visualise the
enormity of geological time and the huge biological
and environmental changes that have occurred, but the
sheer scale of ShapeShift brings that into sharp focus.
Finally, my involvement in this project has also allowed
me to communicate something of my deeply felt
concerns of how important our individual role is in
shaping the landscape around us. By improving our
understanding of what controls environment change,
from mountain-building and the closure of oceans on
timescales of millions of years to rapid climate change
like that occurring today, we have the opportunity to
think more clearly about what the future holds for us,
for the landscape around us and for the ecosystems we
share that landscape with.

* Mesozoic and Cenozoic Stratigraphical Micropalaeontology
of the Dorset coast and Isle of Wight, Southern England,
Editors A.R. Lord and P. R. Bown. Field guide for the 20th
European Micropalaeontological Colloquium, published
by the British Micropalaeontological Society, 1987.