Scientists talk about the 6th mass extinction happening right now. What is it, and how is it different from the last 5?

Five
mass extinctions have already been recorded throughout Earth's history, and we are in the midst
of a sixth. Scientists are not always certain of the cause, but most agree with the idea that
extinctions resulted from climate change. The six mass extinctions are:

• End Ordovician (-444 million years), during which sea levels and temperatures dropped,
  resulting in extinction for 86% of species.
• Late Devonian (-375 million
  years), in which many new plant species evolved and changed the composition of the seas, killing
  75% of species.
• End Permian (-251 million years), called "the great
  dying" and considered the worst mass extinction to date. 96% of species perished, including
  all the corals, nearly ending life on Earth completely.
• End Triassic (-200
  million years), in which Earth lost 80% of species, but scientists are puzzled as to the exact
  reasons why it occurred.
• End Cretaceous (-66 million years), the end of
  most dinosaurs and ammonite sea species. Likely caused by an asteroid impact; 76% of species
  died.
• Present Day: the Sixth Mass Extinction.

It is incredible to think that we are in the midst of a mass extinction today, but all
the evidence is pointing in that direction. Like the others, this one is caused primarily by
rapid climate change. However, there are some significant differences between this sixth
extinction and the other five. Notably, it is occurring all over the world in every climate. No
pockets of life are being spared the effects of this extinction. Countless species of plants and
animals are under threat. Scientists estimate that as many as 50% of all species could become
extinct by the middle of the century.

The most important thing to remember
about this current mass extinction is that humans have made the largest contribution to it.
Human activities have hastened global warming, destroyed habitats, and eliminated endangered
species. At no other point in Earth's history has a species actually, knowingly contributed to
the extinction of others. However, just as humans are the major cause of this crisis, humankind
also has the possibility of moderating it. If humans come together and take action, it is
possible to limit the effects of this extinction and perhaps prevent the worst of it. In that
respect, the sixth extinction is both more frightening, and more inspiring, that the five that
preceded it.

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