Jelaskan Peristiwa kepupusan utama dari Peristiwa kepupusan dalam bahasa melayu

Dalam satu kertas kerja penting yang diterbitkan pada tahun 1982, Jack Sepkoski dan David M. Raup telah mengenal pasti lima kepupusan besar-besaran. Mereka pada asalnya dikenal pasti sebagai penyebab terpisah ("outliers") kepada trend umum penurunan kadar kepupusan semasa Fanerozoik, tetapi ketika ujian statistik yang lebih ketat telah digunakan pada data yang terkumpul, ia didapati bahawa kehidupan haiwan multiselular telah mengalami lima kepupusan besar-besaran utama dan banyak yang lebih kecil. "Lima Kepupusan Besar" tidak boleh ditakrifkan dengan jelas, tetapi sebaliknya kelihatan mewakili yang terbesar (atau yang paling besar) dari suatu peristiwa yang secara berterusan dalam kontinum rata peristiwa kepupusan.

Peristiwa kepupusan Silures-Ordovic (Akhir Ordovic atau  O–S): 450–440 Ma (juta tahun yang lalu) di peralihan Silures-Ordovic. Dua peristiwa berlaku yang membunuh 27% daripada semua keluarga, 57% daripada semua genera dan 60% hingga 70% daripada semua spesies. Secara keseluruhan ia disenaraikan oleh ramai ahli sains sebagai yang kedua terbesar dari lima kepupusan utama dalam sejarah Bumi dari segi peratusan genera yang menjadi pupus.

Kepupusan Ordovic Akhir: 375–360 Ma berhampiran perubahan Karbon-Devonian. Pada akhir zaman Frasnian di bahagian akhir Tempoh Devon, satu siri kepupusan yang berpanjangan menghapuskan kira-kira 19% daripada semua keluarga, 50% daripada semua genera dan sekurang-kurangnya 70% daripada semua spesies.  Peristiwa kepupusan ini berlangsung mungkin selama 20 juta tahun, dan terdapat bukti untuk beberapa siri denyutan kepupusan dalam tempoh ini.

Peristiwa kepupusan Trias-Permian (Permian Akhir): 252 Ma at the Permian–Triassic transition. Earth's largest extinction killed 57% of all families, 83% of all genera and 90% to 96% of all species (53% of marine families, 84% of marine genera, about 96% of all marine species and an estimated 70% of land species, including insects). The highly successful marine arthropod, the trilobite, became extinct. The evidence regarding plants is less clear, but new taxa became dominant after the extinction. The "Great Dying" had enormous evolutionary significance: on land, it ended the primacy of mammal-like reptiles. The recovery of vertebrates took 30 million years, but the vacant niches created the opportunity for archosaurs to become ascendant. In the seas, the percentage of animals that were sessile dropped from 67% to 50%. The whole late Permian was a difficult time for at least marine life, even before the "Great Dying".

Triassic–Jurassic extinction event (End Triassic): 201.3 Ma at the Triassic–Jurassic transition. About 23% of all families, 48% of all genera (20% of marine families and 55% of marine genera) and 70% to 75% of all species became extinct. Most non-dinosaurian archosaurs, most therapsids, and most of the large amphibians were eliminated, leaving dinosaurs with little terrestrial competition. Non-dinosaurian archosaurs continued to dominate aquatic environments, while non-archosaurian diapsids continued to dominate marine environments. The Temnospondyl lineage of large amphibians also survived until the Cretaceous in Australia (e.g., Koolasuchus).

Cretaceous–Paleogene extinction event (End Cretaceous, K–Pg extinction, or formerly K–T extinction):  Ma at the Cretaceous (Maastrichtian) – Paleogene (Danian) transition interval. The event formerly called the Cretaceous-Tertiary or K–T extinction or K–T boundary is now officially named the Cretaceous–Paleogene (or K–Pg) extinction event. About 17% of all families, 50% of all genera and 75% of all species became extinct. In the seas all the ammonites, plesiosaurs and  mosasaurs disappeared and the percentage of sessile animals (those unable to move about) was reduced to about 33%. All non-avian dinosaurs became extinct during that time. The boundary event was severe with a significant amount of variability in the rate of extinction between and among different clades. Mammals and birds, the latter descended from theropod dinosaurs, emerged as dominant large land animals.

Disebalik popular bagi lima peristiwa ini, tidak ada garis pasti yang memisahkan mereka daripada peristiwa-peristiwa kepupusan lain; menggunakan kaedah yang berbeza untuk mengira kesan kepupusan boleh membawa kepada peristiwa lain yang menonjol di lima teratas.

Rekod-rekod fosil yang lebih tua adalah lebih sukar untuk mentafsir. Ini adalah kerana:

Fosil lama lebih sukar dicari kerana ia biasanya tertanam pada kedalaman yang besar.

Memberi tarikh fosil yang lebih tua lebih sukar.

Lapisan fosil yang produktif diteliti lebih daripada yang tidak produktif, dengan itu meninggalkan tempoh tertentu yang kurang dikaji.

Peristiwa alam sekitar prasejarah boleh mengganggu proses pemendapan.

Pemeliharaan fosil berbeza-beza di tanah, tetapi fosil marin cenderung lebih baik terpelihara daripada ia yang dicari oleh rakan-rakan di daratan.

It has been suggested that the apparent variations in marine biodiversity may actually be an artifact, with abundance estimates directly related to quantity of rock available for sampling from different time periods. However, statistical analysis shows that this can only account for 50% of the observed pattern, and other evidence (such as fungal spikes) provides reassurance that most widely accepted extinction events are real. A quantification of the rock exposure of Western Europe indicates that many of the minor events for which a biological explanation has been sought are most readily explained by sampling bias.

Research completed after the seminal 1982 paper has concluded that a sixth mass extinction event is ongoing:

6. Holocene extinction: Currently ongoing.  Extinctions have occurred at over 1000 times the background extinction rate since 1900. The mass extinction is considered a result of human activity.

More recent research has indicated that the End-Capitanian extinction event likely constitutes a separate extinction event from the Permian–Triassic extinction event; if so, it would be larger than many of the "Big Five" extinction events.