Extinctions can occur on a large
scale with many different species, which is known as a mass extinction. Which of the following is a
potential cause of a mass extinction event? (A) An increase in available
sunlight. (B) A decrease in human activities,
such as traveling between countries. (C) Toxic or harmful gases released
from a large volcanic eruption. Or (D) a disease specific to one
species being passed through a population.
A mass extinction refers to the
termination of a large number of species in a relatively short period of time. So, we are talking about a
situation that widely affects all life on Earth and quickly reduces the number of
species all over the world. Common reasons for mass extinctions
include natural disasters, changes in climate, and man-made causes. These all can change an
environment, cause death themselves, and/or make it more difficult for organisms to
find food or reproduce. As a result of any of these, there
may be few-to-no offspring produced by a particular species. Eventually, if no offspring are
produced, once the existing individuals have died, the species will become
extinct. If this is happening for many
species at once due to drastic changes in the world that make survival or
reproduction difficult, we have a mass extinction event.
Let’s look through the answers to
see which describes a situation likely to result in a mass extinction event. An increase in sunlight, as
described in answer option (A), would likely increase photosynthesis and therefore
allow more plant growth. These plants will be available food
for other species. So, this situation would support
more life and would be unlikely to result in many species becoming extinct at the
same time. So, we can eliminate (A).
A decrease in human activities, as
described in answer option (B), would be likely to reduce environmental change. This would allow most species to
continue to live as they always have. Less travel between countries would
likely result in lower carbon emissions, which would reduce the climate change
induced by such emissions. Again, this would result in less
change to the environment. A stable environment is not likely
to cause a mass extinction, quite the opposite. So, we can eliminate (B).
Toxic or harmful gases released
from a large volcanic eruption, as described in answer option (C), describes a
natural disaster with toxic or poisonous effects. This sounds like something that
could cause the death of organisms in the environment where it occurred. Since it is a large eruption, this
could potentially cause enough death to result in many species becoming extinct at
once. So, this looks like it could be our
answer, but let’s check the last choice to be sure.
A disease, like the one described
in answer option (D), can cause an extinction. However, a mass extinction refers
to the extinction of many species at once. Since the disease described would
only potentially result in the extinction of a single species, it would not produce
a mass extinction. So, we can eliminate (D).
Therefore, the only listed
situation likely to be the cause of a mass extinction event is (C): toxic or harmful
gases released from a large volcanic eruption.