26
H. Khozyem
The biosphere is very sensitive to the climatic and environmental change and has
three different types of response to these changes; 1—Mass extinction, 2—Evolution,
and 3—Rising of new genera. Five major mass extinction events took places through
the geologic history, as well as several hyperthermal events led to the evolution and/or
introducing new creatures to the Earth’s record.
During the Mass extinction events, and based on the High-resolution palaeoecological and geochemical studies indicates extensive ecological stress conditions
led to turnover and recovery of different marine genera extended through intervals
lasting millions of years and extends upheavals affecting terrestrial vegetation.
4 Major Mass Extinction Events
4.1 The Ordovician-Silurian Mass Extinction Event (Fig. 3)
A global extinction event is occurring during the Hirnantian Age (445.2–443.8 Ma)
of the Ordovician Period and the subsequent Rhuddanian Age (443.8–440.8 Ma) [50]
of the Silurian Period. Eighty-five percent of life species were extinct. In which onethird of all brachiopod and bryozoan families were disappeared, as well as numerous
groups of conodonts, trilobites, and graptolites [51]. Two main reasons led to the endOrdovician extinction; the first wave of extinction may be linked to rapid cooling
occurred at the end of the Ordovician [5, 52, 53, 10] and the second is caused by
the sea-level fall associated with the glaciation. The drop in sea level would have
drained the large epicontinental seas and reduced the available habitat for organisms
that favored those settings. The CO 2 level is decreased from 5000 to 3000 ppm
during the glaciation, whereas the sea level is lowered by about present level [54].
The combination of the sea-level drop, and reducing ecospace on continental shelves
due to the glaciation, are likely driving agents for the Ordovician mass extinction.
4.2 Late Devonian (Frasnian-Fammenian)
A global extinction event is occurring during 375–360 Ma close to the Devonian–
Carboniferous transition and lasted about 20 Ma [10]. At the end of the Frasnian
Age (Fig. 3). About 19% of all families, 50% of all genera and at least 70% of all
species were extinct [55]. The end of Devonian was marked by a large multi extraterrestrial impacts (Bolide also called fir bale; Fig. 3) Woodleigh, Alamo, Charlevoix,
Warburton and Siljan with diameters of 120, 100, 54, 52 400 km respectively [16,
17, 56]. Late Devonian mass extinction was a series of extinction events [54]. The
first was around 387 Ma extinction in which about 30% of Genera was extinct. The
second, around 374 Ma and about 58% of the pelagic Genera were extinct including
several species of Ammonoids, Cricoconaids, Placoderms, Conodonts, Agnathans,
H. Khozyem
The biosphere is very sensitive to the climatic and environmental change and has
three different types of response to these changes; 1—Mass extinction, 2—Evolution,
and 3—Rising of new genera. Five major mass extinction events took places through
the geologic history, as well as several hyperthermal events led to the evolution and/or
introducing new creatures to the Earth’s record.
During the Mass extinction events, and based on the High-resolution palaeoecological and geochemical studies indicates extensive ecological stress conditions
led to turnover and recovery of different marine genera extended through intervals
lasting millions of years and extends upheavals affecting terrestrial vegetation.
4 Major Mass Extinction Events
4.1 The Ordovician-Silurian Mass Extinction Event (Fig. 3)
A global extinction event is occurring during the Hirnantian Age (445.2–443.8 Ma)
of the Ordovician Period and the subsequent Rhuddanian Age (443.8–440.8 Ma) [50]
of the Silurian Period. Eighty-five percent of life species were extinct. In which onethird of all brachiopod and bryozoan families were disappeared, as well as numerous
groups of conodonts, trilobites, and graptolites [51]. Two main reasons led to the endOrdovician extinction; the first wave of extinction may be linked to rapid cooling
occurred at the end of the Ordovician [5, 52, 53, 10] and the second is caused by
the sea-level fall associated with the glaciation. The drop in sea level would have
drained the large epicontinental seas and reduced the available habitat for organisms
that favored those settings. The CO 2 level is decreased from 5000 to 3000 ppm
during the glaciation, whereas the sea level is lowered by about present level [54].
The combination of the sea-level drop, and reducing ecospace on continental shelves
due to the glaciation, are likely driving agents for the Ordovician mass extinction.
4.2 Late Devonian (Frasnian-Fammenian)
A global extinction event is occurring during 375–360 Ma close to the Devonian–
Carboniferous transition and lasted about 20 Ma [10]. At the end of the Frasnian
Age (Fig. 3). About 19% of all families, 50% of all genera and at least 70% of all
species were extinct [55]. The end of Devonian was marked by a large multi extraterrestrial impacts (Bolide also called fir bale; Fig. 3) Woodleigh, Alamo, Charlevoix,
Warburton and Siljan with diameters of 120, 100, 54, 52 400 km respectively [16,
17, 56]. Late Devonian mass extinction was a series of extinction events [54]. The
first was around 387 Ma extinction in which about 30% of Genera was extinct. The
second, around 374 Ma and about 58% of the pelagic Genera were extinct including
several species of Ammonoids, Cricoconaids, Placoderms, Conodonts, Agnathans,