-
- As the twentieth-century comes to a close,
a recent number of studies looking at a wide range of life suggest one
irrevocable conclusion when viewed in tandem: The world may be on the brink
of a sixth mass extinction.
-
- Scientists have used fossil records in
efforts to piece together the development and death of many long-ago species,
but cutting across this tumultuous evolution of life is a succession of
mass disappearances - at least five globally in the past 500 million years
- followed by rebirth.
-
- The causal agent of past mass extinctions
varies. It is theorized that one such extinction, some 250 million years
ago, was caused by a volcanic outpouring of super-heated rock that rose
from the Earth's lower mantle, some 1,800 miles deep, and broke through
the crust near present-day Siberia, resulting in a vast flood of lava up
to a million times the material spewed out by an eruption such as that
of Mount St. Helens. In fact, the one million cubic kilometers of molten
volcanic rock that is believed to have broken through the surface would've
been enough lava to cover the entire Earth to a depth of 10 feet [1]. The
most recent mass extinction of some 65 million years ago, the popular theory
goes, occurred when an asteroid slammed into the Yucatan area of Mexico.
The dinosaurs, and most everything else living on the planet at the time,
perished in the disastrous ecological aftermath.
-
- While such past worldwide extinctions
have been linked to sudden, catastrophic events, the most recent signs
pointing to a possible "sixth mass extinction" suggest the following
- while the end result would be just as catastrophic, the cause is much
more subtle.
-
- From the land to the sea, and the creatures
both great and small once thriving upon and within, an ever-increasing
number of die-offs are apparently occurring.
-
- Upon the land, close to one out of every
eight plants in the world faces possible extinction due to a loss of habitat
and competition from the introduction of non-native plants. A 20-year study,
by the World Conservation Union, showed some 12.5% of the world's seed-producing
plants and ferns - or nearly 34,000 species in all - to be endangered.
That figure rose to 29% (of plants at risk) in the United States alone.
In the rose family, 14% of species were endangered. In the lily and iris
families, a full 32% were in trouble. Overall, of 270,000 species of vascular
plant (conifers, ferns and flowering plants - but NOT mosses, lichens,
algae & fungi) total, some 33,798 species in 200 countries were found
to be threatened[2].
-
- The world's trees don't fare much better
these days. Some 10% of tree species are at risk of extinction because
of felling, forest fires and poor forest management, a three-year project
by the World Conservation Monitoring Center recently revealed. Specifically,
more than 8,753 of the globe's 80,000 to 100,000 tree species are in danger
of extinction[3].
-
- As the trees go, so does the forest.
More than half of the world's original forest cover has been destroyed,
and that remaining is mostly degraded. Only 22% is considered "frontier"
forest, which is defined (by the World Resources Institute) as "large
intact natural forest ecosystems capable of providing a safe habitat for
all its indigenous species."
-
- Tropical rainforests are disappearing
at an alarming rate. If present rates of deforestation continues, some
experts estimate all such forests will be cleared in about 177 years. Already,
Latin America has lost some 37% of its tropical forests, Asia has lost
42% and even Africa has 52% less [4]. A mere 3% of the world's remaining
frontier forests are in the temperate zone. Originally covering 0.2% of
the Earth's land area, more than half of the planet's temperate rainforests
have already been destroyed. Those remaining are mainly located in two
regions - southern Chile, and an area extending from northern California
to British Columbia and southeast Alaska. A small percentage is spread
throughout the southern hemisphere[5].
-
- Animal species are also in decline. According
to a World Conservation Union study, about one in four vertebrate species
surveyed up to this point is in serious trouble. According to the study's
estimates, some 25% of mammals and amphibian species, 11% of birds, 20%
of reptiles, and 34% of fish species surveyed so far are threatened with
extinction. Another 5% to 14% of species in these groups are nearing "threatened
status" [6]. Scientists estimate that extinction rates are now 100
to 1000 times greater than normal - and rising. Either declining sharply
in numbers or limited to very small populations, species face pressure
from land clearance, excessive hunting or fishing, and the help humanity
- both intentionally and unintentionally - gives to invasive species, further
threatening native fauna.
-
- As people use more water, less is left
for vital ecosystems on which humans and other species depend. Globally,
more than 20% of all freshwater fish species are endangered or vulnerable,
or recently have become extinct. A growing number of saltwater fish are
also facing extinction, due in part to overfishing.
-
- Even human birthrates, in the industrialized
world at least, are in a rapid, sustained decline. Due primarily to prosperity
in the developed world, millions of women are staying in school longer,
working harder and marrying later -- and having fewer children than ever
before.
-
- Never before, except in times of war,
plague and economic depression, have birthrates fallen so low, for so long.
In Europe, there is not one country where people are now having enough
children to replace themselves when they die. Even in the U.S., the birth
average of slightly below 2.1 children per woman, the number needed to
keep the population from beginning to shrink. And while populations in
Africa, India and Asia do continue to sustainably grow, since 1965 the
birthrate has been cut in half, a bigger drop than in the two previous
centuries[7].
-
- Across the globe, species of all kinds
are in decline. Many as a result, directly or indirectly, of the long-reaching
hand of humankind. So, are we on the brink of a "sixth mass extinction"?
According to a recent survey, of 400 biologists, some 7 out of 10 answered
a resounding "yes". They predicted that up to one-fifth of all
living species could disappear within 30 years [8]. Nearly all surveyed
attributed the losses to human activity.
-
- -
-
- [1] "Earth Extinctions Linked to
Lower Mantle Eruptions" A. Basuo, R. Hannigan & S. Jacobsen (University
of Rochester/Harvard University), 'Geophysical Research Letters', July
1998.
-
- [2] "Red List of Threatened Plants"
World Conservation Union, April 1998.
-
- [3] "World List of Threatened Trees",
World Conservation Monitoring Center, August 1998.
-
- [4] International Wildlife Education
& Conservation Factsheet
-
- [5] "Forests in Trouble: Review
of the Status of Temperate Forests Worldwide" N. Dudley, WWF, 1992.
-
- [6] Worldwatch Institute, World Conservation
Union study "Higher Animals Facing Major Declines" May 30, 1998
-
- [7] "World put out fuse on population
bomb" New York Times, July 19 1998.
-
- [8] "Mass Extinction Underway",
Discovery Online, April 20 1998
|
