Daonella beds from QZ480, Aring

Daonella beds from QZ480, Upper Anisian, Middle Triassic
Telong Formation, Aring, Kelantan

Kenali Bumi Anda : Era Mesozoik

Era Mesozoik adalah salah satu era dalam sejarah bumi yang berlansung dari 245 hingga ke 65 juta tahun lampau. Era Mesozoik merangkumi masa antara dua peristiwa penting kepupusan hidupan dalam sejarah bumi iaitu kepupusan Permian dan kepupusan Kapur (Cretaceous). Kepupusan Permian mengakhiri era Paleozoic manakala kepupusan Kapur pula mengakhiri kehidupan dinasor yang juga mengakhiri era Mesozoik. Ahli geologi yang mengkaji bumi membahagi era Mesozoik kepada tiga zaman geologi iaitu Triassik (245-208 juta tahun), Jurassik (208-146 juta tahun), Kapur (146-65 juta tahun).

Pada ketika itu bumi hanya mempunyai satu kerak benua besar sahaja atau dikenali sebagai Pangea. Mesozoik adalah ketika di mana bermulanya pemecahan kerak benua besar tersebut bermula sekitar 225-200 juta tahun lampau yang akhirnya membahagikan kerak benua besar tesebut kepada 13 benua moden seperti yang terdapat hingga kini. Pemecahan ini adalah akibat tindakan pergerakan bahan-bahan magmatik dalam perut bumi dan menjadi punca utama terhadap kejadian gunung berapi dan gempa bumi akibat perlanggaran tektonik antara benua-benua. Pemecahan ini juga meninggalkan kesan yang mendalam terhadap kehidupan bumi yang menyumbang terhadap kepupusannya. Proses pemecahan ini masih berlangsung sehingga sekarang.

Hidupan laut Mesozoic menyaksikan kemunculan semula sepalopod atau haiwan sotong bercangkerang seperti ammonoid (seperti ceratites) yang akhirnya diganti pula oleh ammonit. Terumbu karang, ikan bercangkerang pula terevolusi dan bersaing dengan ammonit sebagai pemangsa.

Hidupan daratan pula menyaksikan kemunculan beberapa kumpulan tetrapod atau haiwan berkaki empat seperti dinasor, reptilia dan mamalia yang mendominasi persekitaran daratan. Tumbuh-tumbuhan baru telah muncul seperti pokok paku pakis (saikad), conifer dan gingko. Tumbuhan berbunga pula mula muncul sekitar 140 juta tahun lampau dan mendominasi banyak kawasan di dunia sehingga kini.

Era Mesozoik berakhir dengan kepupusan massa sekitar 65 juta tahun lampau yang menyaksikan hampir 75% spesies kehidupan bumi pupus sama sekali termasuklah dinasor, reptilian dan ammonit. Punca kepupusan ini telah lama dibahaskan tetapi belum ada konklusi yang tepat boleh ditafsirkan. Namun begitu punca utama yang sering diketengahkan oleh ahli geologi adalah berpunca dari hentaman meteorit-meteorit dari angkasa lepas.

The Mesozoic : The age of dinosaurs

The breakup of Pangea

The Mesozoic era covers the time between two great extinctions: the Permian extinction that closed the Paleozoic era, and the Cretaceous extinction that ended the reign of the dinosours (as well as the Mesozoic). The Mesozoic era is divided into three geologic periods;

• Triassic (245-208 m.a)
• Jurassic (208-146 m.a)
• Cretaceous (146-65 m.a)

The Mesozoic was the time of the beginning of the breakup of Pangea about 225-200 m.a, eventually fragmenting that supercontinent into the modern continents that what we have today. This break had profound consequences for living things, as had the earlier formation of Pangea during the later Paleozoic. The breakup continues today!

Mesozoic seas saw a rise and spread of another iteration of the cephalopods, the ceratites, eventually to be replaced by the ammonites. Coral reefs, which had been decimated by the Carboniferous extinction returned to prominence with the evolution of new groups of reef-building animals and algae. Modern bony fish evolved and began to compete with the ammonites as swimming predators.

Terrestrial animals saw the rise of major groups of tetrapods: dinosaurs and mammals and the later advent of birds. Tetrapods took to new environments in the air as well as a secondary return to the waters. Forests took on an increasingly modern look, with the evolution of cycads and cycadeiods, conifers and gingkgoes. Flowering plants finally appreared about 140 m.a and have risen to become the dominant floral component of many areas of the planet.

The Mesozoic ended with the great mass extinction that eliminated nearly 75% of all species, including dinosaurs, swimming anf flying reptiles and ammonites. The causes of this extinction have long been speculated on and are not presently conclusively settled.

The Kinds of Fossils

Paleontologist are people who study ancient life. They study life forms that are now extinct, they rely on fossils to learn about life in the past.Fossils are the remains of living things that have transformed into stone over millions of years.

Most fossils are found in the sedimentary rock. The Fossils are made when living things die and get buried by sediments quickly before the hardest parts of the animal have a change to decay. As sediments accumulate, pressure causes the sediments to harden into rock: Sand sediments become sandstone, clay sediments become shale or mudstone and shell sediments become limestone.

Groundwater carrying minerals seeps into the sedimentary rock and helps the fossils form in one or two ways. Sometimes the minerals fill in all of the empty places of the once living thing and form crystals. These crystals cause the remains of the living thing to harden along with the sedimentary rock that it is encased in. Petrified wood is an example of this process, which is called permineralization.

At other times, the minerals in the groundwater actually replace the minerals that make up the remains. So over time the hard parts are completely replaced by other minerals. This process is called replacement.

Other important fossils are impressions and molds. These are made when a hard part such as a shell, fills up with sediments that harden, and then the actual shell dissolves leaving nothing but the sediment mold. These mold can tell us much about the body structures of animals and plants.

As well, insect also get trapped in amber, which is fossilized tree sap. In the movie Jurassic Park, scientists use dinosour DNA from the stomachs of mosquitoes trapped in amber to genetically engineer dinosours.

Some animals have even been trapped in ice, too, preserving them extremely well. Woolly mammoths and mastodons have been found with hair intact and bones in good condition. Likewise, some animals and plants have been mummified in hot arid conditions like those found in deserts.

Finally, paleontologist can learn about ancient life from trace fossils. Trace fossils are things like footprints or animal droppings, which can tell us about the animal's behaviour.

How fossils are made

Living things (usually aquatic) die and then get buried quickly under sand, clay or ash sediments. Usually, the soft parts decay or rot away, leaving the hard parts behind. These are ammonoids, one of the most common fossils that are found.

As time goes on more and more sediment accumulates. Pressure, heat and chemical reaction cause the sediments to harden into rock called sedimentary rock. Movement in the earth's crust, pushes the layers of sedimentary rock back up to higher ground.

Finally, through erosion caused by weather, wind and water, the fossils become exposed at the surface again.-IYPE