Travel Reference
In-Depth Information
power of earthquakes has made the true nature of Earth's geological history
far more real to me.
As the Earth's tectonic plates slide and crash into each other in exquisite
slow motion, they produce many local disasters that kill enormous numbers
of individual animals and plants. Nonetheless, most of the volcanic eruptions
and tidal waves have not wiped out whole species. Commonly, extinctions
happen when a species becomes adapted to a narrow ecological niche and
then the niche disappears. Before humans, such niches usually disappeared
because of climate change or the invasion of new species.
If a species inhabits a broad range of niches and is spread over a large geo-
graphic range, then it is unlikely to go extinct. We humans, I suspect, were
already occupying so many ecological niches in dif erent parts of the Old
World at the time of the Toba event that we could easily have survived an
ordinary volcanic eruption, no matter how spectacular.
Even if my earthquake had somehow killed all the manta rays of Yap,
other populations of this widely distributed species would not have been
af ected. A few days after the earthquake I dove on a manta cleaning station
on the island of Pohnpei, 250 kilometers to the east of Yap. The mantas of this
thriving population were being cleaned by wrasses that darted in and out of
their gill slits. It is unlikely that even a force 9 earthquake on Yap would have
af ected the Pohnpei population.
Extinctions are also common when two tectonic plates approach each
other for the fi rst time and a fl ood of new animals and plants pour into a
region. The invaders may ruthlessly take over the niches of the previous
inhabitants. Such encounters happened when North and South America
joined together through the Isthmus of Panama between three and two mil-
lion years ago, ending South America's long isolation. A similar encounter
is taking place in the Indo-Pacifi c as the Australasian and Southeast Asian
plates continue to approach each other. Eventually, even in the absence of
humans, Wallace's Line would have been breached and a fl ood of placental
animals would have reached Australia.
Humans, of course, have accelerated the process. The invasion of Austra-
lia by Europeans and their domestic and wild animals has triggered repeated
ecological disasters. Grazing and urbanization, along with the depredations
