Wanted: Oscar Obsidian - Auckland Museum

Background
As the land area reduced, species that had
evolved here faced advancing waters and
destruction of habitats, creating a biotic bottleneck.
The original Gondwanan flora and fauna
was considerably reduced. Later the survivors
diversified and new species evolved. Wrens, moa
and giant weta were all affected. Some modern
birds are probably descendants of a single surviving
species.
New Zealand did not remain a small archipelago
for long. About 25 million years ago, a plate
boundary started to develop through New
Zealand between the Australian and Pacific
plates.
The collision between these two plates has pushed
up our mountain ranges within the last 6 million
years. Sediments from the continuous erosion of
the mountains has extended our coastlines to create
new land.
Coal and Oil
Coal and oil are evidence of former widespread
lowland swamps with rich plant growth and a
warm climate. Until the beginning of the
Oligocene 35 million years ago, New Zealand's
climate was warmer than today's. Oil is produced
from the breakdown of dead animals and plants
after burial and moderate heating.
Coal results from the accumulation of dead plant
material in swamps which has then been deeply
buried and heated to higher temperatures. There
are a number of coalfields around New Zealand
including the West Coast of the South Island and
the Hauraki Plains area of the North Island.
In the late Cretaceous to Paleocene (70-60 million
years ago) organic matter accumulated, was
buried and turned into oil. During this process, the
oil moves underground to find a reservoir, a
porous rock that soaks the oil up like a sponge.
Reservoir rocks in New Zealand range in age
from Paleocene to Miocene. The Taranaki oilfields
are the most productive in New Zealand.
Climate Change and the Ice Ages
In the course of its history, New Zealand has
changed many times in both location and climate
from subtropical to subantarctic. All have had a
great influence on its plants and animals. The climate
changes are mediated by tectonic movements
as well as more cosmic events. The current
distribution of many indigenous animals is a lega-
Auckland Museum 13
cy of the Pleistocene glaciations which ended
some 10,000 years ago.
During the last 64 million years there has been a
global trend towards a cooler climate. In the
Paleocene and Eocene the oceans were sluggish
and Antarctica had no ice cap. During the
Oligocene the movement of Australia away from
Antarctica and the opening of the Drake Passage
at the bottom of South America allowed the formation
of a cold circumpolar current around
Antarctica. This thermally isolated Antarctica,
allowing an ice cap to form. There was a warming
trend in the late Oligocene- Middle Miocene.
The drop in temperature at the end of the
Miocene is due to the isolation and evaporation of
the Mediterranean Sea. This event decreased the
salinity of the oceans, allowing them to freeze at
higher temperatures. The polar ice cap increased
in size. The uplift of the Himalayas drove drier
winds over Northern Africa, and affected rainfall
in Asia.
Three million years ago, North and South America
joined, terminating warm currents around the
equator and promoting the warm Gulf Stream in
the North Atlantic. The Gulf Stream is responsible
for snowfall on the North Pole, creating the
Northern Hemisphere Ice cap.
A Touch of the Tropics
25 -14 million years ago warm currents from
tropical seas washed New Zealand shores and the
climate was subtropical. Coconuts, corals and
cone shells flourished. Warmth-loving plants
established. Some died out later when the climate
cooled again, others adapted and stayed.
The Ice Ages
Earth's climate has swung between warm and cold
about 50 times in the last 2.6 million years.
During particularly cold periods called Ice Ages
or Glaciations, ice sheets grew on the continents
causing sea levels to drop up to 120 m. The frequency
and regularity of the oscillations tell us
that it is changes in Earth's orbit that controls the
amount of heat reaching Earth's surface
The ice age climate had a large impact on New
Zealand's flora. This included the expansion of
grasslands in both islands and the growth of
alpine shrubs and herbs at much lower elevations
than today.