The vast majority of all species who have ever lived on earth no longer exist. far more organisms have become extinct than are currently alive. why? a. species are continually being replaced or changed into other species by evolution. this process is currently very rapid compared to how long life has existed on earth. b. over the past two million years, human interference has continually and significantly decreased animal and plant biodiversity. c. mass extinction events like meteor impacts and climate changes have destroyed most life on earth. d. the biodiversity of life on earth continually decreases as natural selection eliminates species that are less fit for survival.