Geology Reference
In-Depth Information
Asteroid impact:
Recently, scientists have presented evidence for a possible im-
pact event that may have led to the extinction of North American megafauna. Re-
searchers are still hotly debating this possibility and looking for evidence (such as
where such an impact may have occurred) to support their hypotheses.
Climate change:
Other scientists claim that climate changes occurring at the same
time, such as ice age glaciers melting and global conditions becoming warmer,
were significant enough to lead some species into extinction. However, the climate
change hypothesis leaves skeptics wondering why large mammal species didn't
migrate to new habitats as the environments changed. And others suggest that the
climate didn't change quickly or dramatically enough to result in extinctions.
Reducing biodiversity
The human effect on megafauna, or large mammals, is far from over. Today, many of the
animals listed as threatened or endangered by humans are the largest existing mam-
mals, including the American bison, Asian elephants, mountain gorillas, various species
of whales, and many species of bear. As humans continue to dominate the earth, the pat-
tern of humans moving into new regions and leading species to extinction is ongoing.
Human population growth and expansion into new ecosystems threatens many species
with extinction. While a background rate of extinction is normal and expected, some
eco-
logists
(scientists who study ecosystems) suggest that humans have increased the ex-
tinction rate by up to 10,000 times its normal rate.
The existence of multiple species is called
biological diversity
or
biodiversity.
Scientists
realize that biodiversity is very important because ecosystems with high biodiversity
are more likely to adapt in response to disturbances (such as wildfires). Richly biodi-
verse regions like the rainforests of South America are also home to species of plants, in-
sects, and animals that may have important and undiscovered medicinal properties.
The most damaging effect humans have on biodiversity is the destruction, fragmenta-
tion, and pollution of ecosystems. Many of the most biodiverse regions are also the
most fragile and are easily damaged by the building of roads, introduction of non-native
species (or farm animals), industrial pollution, and deforestation. If these species be-
come extinct, whether due to human-caused climate change or development and land
use, humans may lose something of great value that they didn't even know they had!
