re life on earth or elsewhere in article may julian uwo ca jdnicoll prism ccs uwo ca james davis nicoll writes in article c z ax kcx cs cmu edu tm msu edu tom writes what evidence is there that there is a trend towards greater species diversity over time what i see going on right now is a major extinction event and it isn t clear to me that the diversity k years ago was necessarily greater than million years ago well there are several bursts in species diversity i can think of the cambrian and ordovician explosions resulted in a vast increase in animal diversity likewise after the one two punch of the permian and triassic extinctions the number of marine animals rose steadily to an all time high just prior to the spread of humans biggest exception being the k t bye bye dinos extinction about families also plants arose from green algae and colonized the land in succesive sweeps mosses colonized very wet environments first ferns who had evolved vascular tissues took over more territory when they evolved these were eventually mostly replaced by gymnosperms pines and the like and then mostly displaced by angiosperms flowering plants now the dominant plant group on the planet fungi also radiated greatly with the invasion of the land around the carboniferous up to about families around the triassic up to maybe families starting in the cretaceous rising to about families currently it s unclear to me at least what the max equilibrium number of species the earth can hold and if it has ever hit this in the past it could be warning speculation alert that diversity has never reached a peak because mass extinctions happen often enough to keep the total number down this would depend a great deal on how fragmented specific ecosystems were see cowen s book history of life for a not too technical run down on well like the title sez the history of life or see wilson s diversity of life for a view centered more on current ecology this is imho the best popular biology book of what the hell i ll say it all time james nicoll follow ups to t o chris colby email colby bu bio bu edu my boy he said you are descended from a long line of determined resourceful microscopic tadpoles champions every one kurt vonnegut from galapagos
