Question

Explain some of the ways in which mass extinctions of organisms may have occurred.

Answer 1

​Mass extinction refers to a complete ruling out/disappearance of a particular genus, or species or family of an organism or in otherwords a branch in the phylogenetic tree getting vanished.

Examples of mass extinctions and assumptions on how they would have occured:

1. Ordovician-silurian extinction where small marine organism were gone extinct 440 million years ago

It thought to be occured due to massive icing of water, which drastically led to the decreased sea levels with serious consequence on shelled brachiopods, trilobites and conodonts

2. Devonian Extinction in which many marine species went extinct 365 million years ago

Several reasons like Global anoxia, tectonic plates violent movement, drastic sea level changes, asteroid impacts and climatic changes are named for this mass extinction

3. Permian-Triassic Extinction which can be describeda as the largest mass extinction that resulted in extinction of large range of species that comprised of many vertebrates which took place 250 million years ago

The reason for this mass extinction was believed to be due to asteroid/ comet collison (eventhough there was no evidence of crater found). Hence there is one more assumption for the explanation of this extinction that atttributes to Flood volcanism arised from Siberia in Russia. Some also believe that a high impact served as the reason for the volcanic eruption.

4. Triassic-Jurasic Extinction that occured 210 million years ago resulted in extinction of most vertebrate species that led to the predominance of Dinosaurs

Floods of lava in central Atlantic Magma filled province or an asteroid impact are attributed as the reasons for this extinction.

5. Cretaceous-tertiary extinction that cleared as many as 50% of plants and animals from the face of the earth occured 65 million years ago.

Huge crater in Mexico's Yucantan peninsula is taken as an evidence which explains an extraterrestrial impact that led to the cretaceous extinction. Second assumption is that, Global warming caused due to volcanic eruptions from Deccan regions in India is responsible for this extinction.

Sixth and rapidly evolving extinction is emanating due to man made causes(ex.pollution, disruption of ecosystem,overexploitation of natural resources, deforestation, extensive agriculture techniques) which if calculations were to be proven right, thought to be by the year 2100, can take away most of the plants and animals from the face of the earth.