Travel Reference
In-Depth Information
of rabbits, feral domestic cats, and red foxes have driven about 10% of Aus-
tralia's native marsupial species to extinction. Many more native species are
threatened. Australia is home to about 10% of the world's endangered spe-
cies, even though it makes up only 5% of the planet's land area and much of
it is harsh desert.
Truly titanic events
The many extinctions that have been triggered or aided by climate change
and the movement of tectonic plates, while individually tragic, are an
unavoidable part of the story of evolution. The other side of the coin is that
the destructive power of these events has opened up many opportunities for
evolutionary change.
Ordinary and extraordinary earthquakes and eruptions help to move
the continents along, but for the most part they have little ef ect on evolu-
tion. At the extreme end of this distribution, however, lie geological catas-
trophes that have a truly extreme impact. At least fi ve times in the history of
multicellular life, the Earth has been hit by disasters so immense that even
many widely distributed species have been driven extinct. As we saw ear-
lier, the most dramatic of these extinction events occurred 250 million years
ago, not long before the breakup of Gondwanaland. Straddling the bound-
ary between two great geological periods, the Permian and the Triassic, it is
known as the Permo-Triassic extinction.
There seem to have been two events, closely spaced in time that contrib-
uted to the extinction. They involved massive volcanic eruptions so severe
that the chemistry of the atmosphere and the ocean was changed. The erup-
tions, which racked a vast region of what is now Siberia, covered 2.5 million
square kilometers with lava deposits as much as 3 kilometers thick.
Those events killed most life on the Earth. Some of the lucky survivors
were given unprecedented opportunities, however. It was not long afterward
that both dinosaurs and mammals appeared.
These new groups of organisms were part of a general long-term
