Učitava se

Kucajte za pretragu

Pet velikih masovnih izumiranja na Zemlji, počelo i šesto

Svet uPoMoc

Pet velikih masovnih izumiranja na Zemlji, počelo i šesto

Podeli

Brojni naučnici procenjuju da se Zemlja nalazi na početku novog „masovnog izumiranja“, fenomena koji karakteriše nestanak vrsta u alarmantnom broju za relativno kratko vreme, ovog puta izazvanog ljudskim aktivnostima.

U proteklih 500 miliona godina, planeta je pet puta bila svedok perioda tokom kojih je u treptaju oka geološke istorije nestalo više od polovine živih bića.

Sveukupno, više od 90 odsto vrsta koje su nekada hodale, plivale, letele ili puzale Zemljom sada je izumrlo.

Prvo masovno izumiranje odigralo se pre oko 445 miliona godina. U takozvanom „Ordovicijsko-silurijskom izumiranju“ nestalo je izmedju 60 i 70 odsto vrsta.

Veruje se da je do tog istrebljenja dovelo kratko ali veoma snažno ledeno doba.

U to vreme se živi svet najvećim delom nalazio u okeanima. Naučnici smatraju da je brzo formiranje glečera zamrzlo najveći deo vode na planeti i dovelo do drastičnog pada nivoa mora. Morski organizmi poput sundjera i algi su najviše stradali, kao i školjke, primitivni glavonošci i ribe bez vilica zvane ostrakodermi.

Zatim je pre oko 360 do 375 miliona godina usledilo tzv. „Kasnodevonsko izumiranje“, u kom je nestalo do tri četvrtine živog sveta. Ponovo su najviše stradali morski organizmi, usled smanjenja količine kiseonika u okeanima.

Kao najverovatniji uzroci takvog razvoja dogadjaja navode se variranje nivoa okeana, klimatske promene ili čak udar asteroida. Prema jednoj teoriji širenje kopnene vegetacije dovelo je do manjka kiseonika u vodama. Verovatno najpoznatija žrtva „Kasnodevonskog izumiranja“ bili su trilobiti, artropodi koji su živeli na okeanskom dnu.

Posebno razorno bilo je „Permsko-trijasko izumiranje“, pre oko 252 miliona godina. Taj period, nazvan i „majka svih izumiranja“, odneo je 95 odsto vrsta.

Izazvana po svoj prilici udarima asteroida i vulkanskom aktivnošću, ta biološka kriza je opustošila i okeane i kopno. Neki naučnici veruju da je trajala milionima godina, dok drugi smatraju da je trajala samo 200.000 godina.

To je bio jedini put da su masovno nestali insekti. Nestale su i poslednje preživele vrste trilobita, kao i neke vrste ajkula i riba. Na kopnu, istrebljeni supored ostalih i mošopi, više metara dugi gmizavci biljojedi.

Naredno je usledilo „Trijasko-jursko izumiranje“ i nestanak 70 do 80 odsto vrsta, zbog brojnih i ne do kraja razjašnjenih razloga. Prema jednoj teoriji, okidač su bile masivne erupcije lave usled razbijanja superkontinenta Pangee, što je pratilo i oslobadjanje velikih količina ugljen-dioksida koje je dovelo do brzih klimatskih promena. Iako neki naučnici sumnjaju i na asteroide, do sada nije pronadjen nijedan krater.

Na prelazu iz perioda trijasa u juru nestale su brojne vrste velikih kopnenih životinja, medju kojima i najveći broj arhosaurusa, predaka dinosaurusa ali i današnjih ptica i krokodila. Istrebljen je i najveći deo vrsta džinovskih vodozemaca.

Za sada poslednje, i verovatno najpoznatije masovno izumiranje desilo se na kraju perioda krede, pre 66 miliona godina, po svoj prilici zaslugom asteroida koji je udario područje današnjeg meksičkog poluostrva Jukatan i ostavio ogroman krater. Izumrli su svi neleteći dinosaurusi, ali su na kopnu preživeli najveći broj vrsta sisara, kornjače, krokodili, žabe i ptice. U morima su opstale ajkule, morske zvezde i ježevi.

Nestanak dinosaurusa je omogućio širenje sisara, koje je na kraju dovelo do nastanka homosapijensa, vrste odgovorne za izvesno šesto masovno izumiranje.

U Parizu je trenutno u toku skup naučnika i diplomata iz više od 130 zemalja koji posle 15 godina rade globalnu procenu ekosistema.

Autor/Izvor Beta

23 Komentara

  1. I just want to tell you that I am just very new to blogging and site-building and honestly liked you’re web site. Most likely I’m planning to bookmark your site . You certainly come with tremendous writings. Thank you for revealing your blog site.

    Одговори
  2. I your writing style truly enjoying this website .

    Одговори
  3. health and fitness 28/09/2019

    What i do not understood is in reality how you’re not actually a lot more well-appreciated than you may be right now. You are so intelligent. You already know thus considerably in relation to this subject, made me individually consider it from numerous varied angles. Its like men and women are not fascinated unless it’s one thing to do with Girl gaga! Your individual stuffs great. At all times deal with it up!

    Одговори
  4. health and fitness 28/09/2019

    I am not sure where you’re getting your information, but great topic. I needs to spend some time learning much more or understanding more. Thanks for magnificent info I was looking for this information for my mission.

    Одговори
  5. health and fitness 29/09/2019

    You have remarked very interesting details! ps decent internet site.

    Одговори
  6. health and fitness 02/10/2019

    It¡¦s actually a great and helpful piece of information. I am happy that you just shared this helpful info with us. Please stay us up to date like this. Thank you for sharing.

    Одговори
  7. health and fitness 02/10/2019

    I simply wished to say thanks once again. I am not sure the things that I could possibly have used in the absence of the actual suggestions shown by you on such a field. It seemed to be a alarming problem in my view, nevertheless coming across your skilled strategy you treated it forced me to jump over delight. I am happy for the help and thus expect you recognize what an amazing job you happen to be doing instructing some other people via your blog. I know that you have never got to know any of us.

    Одговори
  8. health and fitness 02/10/2019

    Some truly nice and useful information on this internet site, as well I believe the layout holds great features.

    Одговори
  9. health and fitness 02/10/2019

    You can definitely see your enthusiasm in the paintings you write. The world hopes for more passionate writers such as you who are not afraid to mention how they believe. Always follow your heart. „In order to preserve your self-respect, it is sometimes necessary to lie and cheat.“ by Robert Byrne.

    Одговори
  10. health and fitness 03/10/2019

    I definitely wanted to construct a small note to say thanks to you for all the pleasant ways you are showing on this site. My rather long internet look up has at the end of the day been recognized with reliable insight to go over with my classmates and friends. I ‘d declare that most of us site visitors are definitely lucky to live in a remarkable website with so many outstanding professionals with valuable concepts. I feel somewhat blessed to have used your entire weblog and look forward to many more cool moments reading here. Thank you once again for all the details.

    Одговори
  11. asia trip 04/10/2019

    I like what you guys are up also. Such smart work and reporting! Carry on the superb works guys I have incorporated you guys to my blogroll. I think it will improve the value of my site 🙂

    Одговори
  12. dogs food 05/10/2019

    Thanks a bunch for sharing this with all people you actually recognize what you’re speaking approximately! Bookmarked. Please additionally visit my site =). We will have a link exchange arrangement between us!

    Одговори
  13. health and fitness 06/10/2019

    Some really nice and utilitarian information on this web site, as well I think the style has got great features.

    Одговори
  14. health and fitness 07/10/2019

    You made some clear points there. I looked on the internet for the topic and found most persons will approve with your blog.

    Одговори
  15. health and fitness 07/10/2019

    Great ¡V I should certainly pronounce, impressed with your website. I had no trouble navigating through all the tabs and related information ended up being truly easy to do to access. I recently found what I hoped for before you know it in the least. Quite unusual. Is likely to appreciate it for those who add forums or anything, web site theme . a tones way for your customer to communicate. Nice task..

    Одговори
  16. health and fitness 08/10/2019

    Fantastic site. A lot of useful info here. I’m sending it to a few friends ans additionally sharing in delicious. And obviously, thank you on your effort!

    Одговори
  17. mental health 14/10/2019

    I will right away snatch your rss as I can not to find your e-mail subscription link or e-newsletter service. Do you’ve any? Kindly permit me recognise so that I could subscribe. Thanks.

    Одговори
  18. I actually wanted to develop a simple comment in order to say thanks to you for these marvelous secrets you are giving out here. My particularly long internet search has finally been rewarded with pleasant points to talk about with my good friends. I would suppose that many of us readers actually are undeniably fortunate to be in a very good website with very many outstanding professionals with very helpful solutions. I feel extremely blessed to have encountered your website and look forward to some more cool times reading here. Thank you again for everything.

    Одговори
  19. Kasey Swanzy 15/10/2019

    The guidelines you provided here are really useful. It was such an enjoyable surprise to have that awaiting me as i woke up this very day. They are constantly to the point and easy to understand. Thanks for your time for the innovative ideas you’ve shared above.

    Одговори
  20. Security Finance 15/10/2019

    I simply had to say thanks again. I do not know the things I would’ve achieved in the absence of those opinions provided by you regarding that topic. Completely was a very terrifying concern in my view, but being able to see a new skilled style you processed the issue made me to weep over joy. Extremely grateful for this work and trust you comprehend what an amazing job that you’re providing teaching the rest through your web page. I am sure you have never encountered any of us.

    Одговори
  21. Synthia Condi 16/10/2019

    How do you stop yourself from becoming bored when writing a book?

    Одговори
  22. learn this here now 16/10/2019

    I simply want to mention I am beginner to blogs and definitely loved your web-site. Likely I’m planning to bookmark your blog post . You definitely come with exceptional writings. Cheers for sharing with us your web page.

    Одговори
  23. Thaddeus Boenisch 16/10/2019

    I know a person who knows how to solve this. He is a respected professor from the educational site about technology and the internet.

    Одговори

Ostavite komentar

Vaša e-mail adresa neće biti javno prikazana.

Obavezna polja su obeležena sa *

Slušajte program Radio Luna u mp3 formatu

×