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201922Apr15:15

Impact of cli­mate on global bio­di­ver­sity revealed by new and detailed map­ping of his­tor­i­cal biodiversity

Infor­ma­tion
pub­lished 22 April 2019 | mod­i­fied 22 April 2019

Pale­on­tol­o­gists of the Nat­ural his­tory muse­ums in Copen­hagen and Helsinki have suc­ceeded in map­ping his­tor­i­cal bio­di­ver­sity in unprece­dented detail. For the first time, it is now pos­si­ble to com­pare the impact of cli­mate on global bio­di­ver­sity in the dis­tant past – a result that paints a gloomy pic­ture for the preser­va­tion of present-​day species rich­ness. The study is first pub­lished on 25 March in the jour­nal Pro­ceed­ings of the National Acad­emy of Sci­ences (PNAS).

Polar bear in Hudson BayPolar bear (Ursus mar­itimus) lying on the rocks near the coast­line of Hud­son Bay.
Credit Chris Bobkowski, blog­ger on Earth​watch​.org

The diver­sity of life on Earth is nearly unimag­in­able. There is such a wealth of organ­isms that we lit­er­ally can’t count them all. Nev­er­the­less, there is broad con­sen­sus that bio­di­ver­sity is in decline and that Earth is in the midst of a sixth extinc­tion event – most likely due to global warm­ing. The sixth extinc­tion event reflects the loss of plant and ani­mal species that sci­en­tists believe we are now fac­ing. It is an event that, with over­whelm­ing prob­a­bil­ity, is caused by human activity.

One of the prob­lems with the hypoth­e­sis of global warm­ing is that it is dif­fi­cult to pre­dict what hap­pens to ecosys­tems and bio­di­ver­sity as the planet warms. By exam­in­ing ani­mals of the past and species adapt­abil­ity, we can more accu­rately respond to the ques­tion of what leads to crises in ecosys­tems, and what hap­pens thereafter.

Chris­t­ian M. Ø. Ras­mussen, lead author, Nat­ural His­tory Museum of Den­mark, Uni­ver­sity of Copenhagen

Assis­tant Pro­fes­sor Chris­t­ian Mac Ørum Ras­mussen, who led this ground­break­ing study, fur­ther explains, “thus far, it has been a big prob­lem that some of the largest fluc­tu­a­tions in bio­di­ver­sity through geo­log­i­cal time have been excep­tion­ally tough to grasp and accu­rately date. As such, it has been dif­fi­cult to com­pare pos­si­ble envi­ron­men­tal impacts and their effects on bio­di­ver­sity. Among other things, this is because cli­mate change takes place quite abruptly, in a geo­log­i­cal per­spec­tive. As pre­vi­ous cal­cu­la­tions of bio­di­ver­sity change in deep time have been based on a time-​binning par­ti­tion­ing divided into 1011 mil­lion year inter­vals, direct com­par­isons with cli­mate impacts have not been pos­si­ble. Our new bio­di­ver­sity curves pro­vide unprece­dent­edly high tem­po­ral res­o­lu­tion, allow­ing us to take a very large step towards the under­stand­ing and coher­ence of climate-​related and envi­ron­men­tal impacts on over­all bio­di­ver­sity – both in rela­tion to species devel­op­ment and extinc­tion event intervals.”

A new method
Researchers at the uni­ver­si­ties of Copen­hagen and Helsinki have devised a new method that can pro­vide unprece­dented accu­racy in the por­trayal of bio­di­ver­sity fluc­tu­a­tions on geo­log­i­cal time scales. This has lead to new insight, both in rela­tion to what spurred the largest marine spe­ci­a­tion inter­val in Earth’s his­tory, as well as to what caused our planet’s second-​largest mass extinc­tion event. This method has deployed, among other things, big data and the pro­cess­ing of large quan­ti­ties of infor­ma­tion col­lected on fos­sils, cli­mate and his­toric geo­log­i­cal changes. The study cov­ers a pre­his­toric period char­ac­ter­ized by dra­matic changes to Earth’s cli­mate and envi­ron­ment. Among other things, it doc­u­ments increas­ing lev­els of oxy­gen and heavy vol­canic activ­ity as well as impor­tant events that doc­u­ments the rise in the num­ber of mul­ti­cel­lu­lar marine species, such as dur­ing the Cam­brian Explo­sion.

The stud­ies we have been engaged with for over four years have, for the first time, made it pos­si­ble to com­pare devel­op­ments related to bio­di­ver­sity with cli­mate change, for exam­ple. We are now able to see that pre­cisely when ocean tem­per­a­ture fell to its cur­rent level, there was also a dra­matic increase in bio­di­ver­sity. This sug­gests that a cooler cli­mate – but not too cold – is very impor­tant for con­serv­ing bio­di­ver­sity. Fur­ther­more, we find that the very large extinc­tion event at the end of the Ordovi­cian period (485443 mil­lion years ago), when upwards of 85% of all species dis­ap­peared, was not “a brief ice age” – as pre­vi­ously believed – but rather a sev­eral mil­lion years long cri­sis inter­val with mass extinc­tions. It was most likely prompted by increased vol­canic activ­ity. It took nearly 40 mil­lion years to rec­tify the mess before bio­di­ver­sity was on a par with lev­els prior to this period of vol­canic caused death and destruc­tion,” empha­sizes Chris­t­ian Mac Ørum Rasmussen.

Extinc­tion events
It is widely accepted that there have been a con­sid­er­able num­ber of large extinc­tion events through­out Earth’s his­tory, with five major extinc­tion events in par­tic­u­lar, the “Big Five”. These are the three largest:

  1. The largest extinc­tion event occurred 250 mil­lion years ago, at the end of the Per­mian geo­logic period. 95% of all species are believed to have dis­ap­peared as a result of a cat­a­stro­phe sus­pected to be due to vol­canic activity.
  2. The sec­ond largest extinc­tion event occurred 443 mil­lion years ago, at the end of the Ordovi­cian geo­logic period. Until now, it was believed that a sud­den global cool­ing pre­cip­i­tated this event, dur­ing which up to 85% of all species became extinct. The new study pub­lished in PNAS does away with this assump­tion and points at vol­can­ism as the main reason.
  3. The most recent major extinc­tion event took place 66 mil­lion years ago, when dinosaurs and other forms of life on Earth became extinct. Vol­can­ism and meteor-​impact events on Earth are thought to have caused the dis­ap­pear­ance of up to 75% of all species.

Today, researchers are talk­ing about the planet being in a sixth extinc­tion event prompted by human-​induced change, includ­ing global warming.

Work­ing meth­ods
Among other things, the researchers have made use of a large data­base known as ‘the Pale­o­bi­ol­ogy Data­base ‘. It con­tains data about fos­sils col­lected from across the planet and from dif­fer­ent peri­ods of Earth’s geo­log­i­cal his­tory. Until now, pulling data to pro­vide an over­all pic­ture and assess­ment of the global sit­u­a­tion with high tem­po­ral res­o­lu­tion has not been pos­si­ble due to the ardu­ous nature of the process. The new study has over­come this obsta­cle by first con­struct­ing a glob­ally defined schema of ‘time inter­vals’ that divided a 120 million-​year-​long period into 53 ‘time bins’. They then jux­ta­posed these bins of time with rock for­ma­tions in which fos­sils were found. Then, the researchers analysed their data using a sta­tis­ti­cal method typ­i­cally used by biol­o­gists to cal­cu­late the preva­lence of ani­mal life in a given area. The pale­on­tol­o­gists used the method to cal­cu­late the diver­sity of gen­era per time bin, as well as ‘to pre­dict’ how many gen­era ought to occur in sub­se­quent time bin. Not only did this method­ol­ogy allow for researchers to achieve an unprece­dented high tem­po­ral accu­racy, it also let them account for any lack­ing fos­sil remains over geo­log­i­cal time.

(Source: Uni­ver­sity of Copen­hagen press release, 04.04.2019)


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