A keystone in a changing world - Antarctica: Global Science from a Frozen Continent - page 48

Figure 2.15 The Carboniferous Ice World showing how
a large ice sheet covered much of the Gondwana
supercontinent about 300million years ago. (Credit:
Bryan Storey)

Carboniferous Ice World
289 Ma

ancient Gondwana supercontinent during
the Carboniferous period about 300million years
ago. A thick ice sheet covered much if not all of
Antarctica, waxing and waning and depositing
glacial moraines, now preserved as thick glacial
deposits in the Ellsworth Mountains and in the
Transantarctic Mountains. As the ice moved over
the underlying land surface, boulders locked in the ice cut furrows and grooves,
providing a further record of the passage of these great ice sheets long after they
disappeared.
After the Carboniferous ice world, climate warmed and there was rapid
evolution of a rich

Ice sheet

flora. Extensive cool-temperate swamps with thriving plant
communities formed coal deposits, which can now be seen as thick coal seams
stretching along the length of the Transantarctic Mountains. In fact, over 100 years
ago, Edward Wilson, as he made his way up the Beardmore Glacier as a member
of Scott ' s Polar party, realised from these conspicuous coal horizons and from

finding fossil leaves that Antarctica had been very different from today and not
always the cold barren icy landscape that he was experiencing. Some of the most
beautiful and distinctive fossils entombed in these Gondwana coal measures are the
leaves of the ancient deciduous tree, Glossopteris . Early Ginkgos and conifers also
appeared in the fossil record in Antarctica and the once neighbouring continents of
Gondwana (e.g. Australia, India, etc.). They colonised the drier hillsides and were
not restricted to swamps. Tree ferns similar to those alive today were abundant.
The climate warmed up gradually after the ice age. Nevertheless it was a cold
climate for much of this period. The Permian Glossopteris flora is one of the most

characteristic fossil assemblages of the Gondwana supercontinent. The discovery
of these fossils on the now widely distributed Gondwana continents of South
America, Africa, Australia and India provides important supporting evidence
for the theory of continental drift and plate tectonics. Unfortunately, you will not

find any descendants of the glossopterids alive today. They were wiped out by the
end-Permian extinction event, the Earth s most severe extinction event, with up to

96% of all marine species and 70% of terrestrial vertebrate species becoming extinct.
There are several proposed mechanisms for the extinctions; an earlier peak was
likely due to gradual environmental change (including sea-level change, anoxia
and increased aridity), while a later peak was probably due to a catastrophic event

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