Around the year 1000, it's a reasonable guess to assume that emergence of new species and species extinction were roughly in balance, so net extinction rate was indeed around 0.
Today, it's well-established that this net extinction rate is as horrible as is described. A few new species emerging here and there are not enough to compensate for the mess that we are causing on the extinction front, by orders of magnitude.
Around the year 1000, it's a reasonable guess to assume that emergence of new species and species extinction were roughly in balance, so net extinction rate was indeed around 0.
Today, it's well-established that this net extinction rate is as horrible as is described. A few new species emerging here and there are not enough to compensate for the mess that we are causing on the extinction front, by orders of magnitude.