What does “empirically derived” mean?

http://advances.sciencemag.org/content/1/5/e1400253.full

Questions for summary (discussed in class):

1.Which questions were addressed by the authors for this particular paper?

2.What does “empirically derived” mean?

3.How do the authors justify the questions asked?

4.What is considered to be “modern extinction”?

5.What are the five vertebrate taxa considered in this study?

6.The authors focused on using conservative rates of modern extinction in
order to avoid skepticism and to see if the use of the term “6th mass
extinction” is still justified. They used two different categories: “highly
conservative rates” and “conservative rates”. What were the criteria used
for each category (see Table 1)?

7.Why is 1900 considered separately from 1500 as the time for modern
extinction rates?

8.What was the range found for modern extinction rate in relation to
background extinction rates?

9.How many years would it have taken for the vertebrates that went
extinct in the last century to go extinct if the background extinction rate
had prevailed?

10.According to the authors, how does the loss of biodiversity affect
human well-being?

11.Outside of human well-being, why do you think we should care about the
loss of biodiversity?

12.What do the authors conclude from this analysis?

13.On a human time scale, do the authors consider the loss of biodiversity
(and biodiversity benefits) permanent? Why or why not?

14.What suggestions do the authors make to avoid such loss (specifically,
what are three notably important issues that must be urgently dealt with)?