Salon] Earth has already witnessed five mass extinctions — devastating events that wipe out the majority of life on the planet. The Cretaceous-Tertiary extinction event (known as the K/T extinction, for short), was likely caused by an asteroid colliding with Earth, and caused the dinosaurs to disappear. A more recent extinction event, “The Great Dying,” was likely caused by a volcanic event.
we are likely at the brink of a sixth mass extinction. By 2070, the
majority of coral reefs on Earth could vanish, killing 25 percent of all
fish species in the process. Earth’s wildlife population has decreased
by 50 percent in the last 40 years alone. With a drastically changing
climate already taking its toll on our environment, we can expect to see
many more changes like these in the near future.
Salon spoke with evolutionary biologist and host of the documentary “Mass Extinction: Life at the Brink,” Sean B. Carroll to learn more about our (possibly) impending doom.
This interview has been lightly edited.
What exactly is a mass extinction?
there are some definitions out there, but let’s just say that when the
majority of species on the planet disappear in a relatively short period
of time. Here comes the parentheses part … Some define it as 75 percent
but it’s very hard to know what 75 percent of life on Earth is at a
given time. You know, just because of the sparsity of the fossil record
and things like that. You can ask me more technically. But so let’s just
say it’s the majority and they stand out against sort of the background
pattern of extinction. So, if you just plot the known diversity of life
on the planet at any given time there are these pretty dramatic drops
and they’ve been known for a long time in the rock record, because it
turns out they coincide with pretty dramatic changes in the rocks
themselves. So, you can sort of see from the rock record that
something’s happened on the planet and it turns out that those tend to
be boundaries where there’s a pretty dramatic change between life before
and life after that phase in time. Geologists have been naming rocks
for a long time. This goes back a couple of centuries and it just turns
out that the boundaries between the big phases of time often are
boundaries between eras of life marked by the extinction of the previous
era and in the appearance of new kinds of things. Read More