Rest of it is believed to be "dark matter" which states -
"Scientists have some ideas about what dark matter might be—exotic and still hypothetical particles—but they have hardly a clue about dark energy. … University of Chicago cosmologist Michael S. Turner ranks dark energy as “the most profound mystery in all of science.”
your quote doesn't say what you implied^^;
also at the mass extinctions, those of the pasts were of a very different nature and more rapide than our influence. additionally we as mankind have a choice, so it shouldn't be treated as just the 6th round of it.