Primeval 8 – Ordovician Period

 

The Great Ordovician Biodiversification Event (GOBE) was a diversification of animal life throughout the Ordovician period,(1)Axel Munnecke et al. (2010). “Ordovician and Silurian sea-water chemistry, sea level, and climate: A synopsis” Palaeogeography, Palaeoclimatology, Palaeoecology, Volume 296, Number 3–4, Pages 389–413 just 40 million years after the Cambrian explosion.(3)Thomas Servais et al. (2008) “The Ordovician Biodiversification: revolution in the oceanic trophic chain” Lethaia, Volume 41, Number 2, Page 99 During the GOBE, the distinctive Cambrian animals died out to be replaced with Palaeozoic animals, most of which were alga-eaters and coastal fish.(2)Thomas Servais et al. (2010) “The Great Ordovician Biodiversification Event (GOBE): the palaeoecological dimension” Palaeogeography, Palaeoclimatology, Palaeoecology, Volume 294, Number 3–4, Page 99 It followed a series of extinction events at the Cambrian-Ordovician boundary, and the resulting animals went on to dominate the Palaeozoic relatively unchanged.(4)Mary L. Droser and Seth Finnegan (2003) “The Ordovician Radiation: A Follow-up to the Cambrian Explosion?” Integrative and Comparative Biology, Volume 43, Page 178 Marine diversity increased to levels typical of the Palaeozoic,(5)Charles R. Marshall (2006) “Explaining the Cambrian “explosion” of Animals” Annual Review of Earth and Planetary Sciences, Volume 34, Pages 355–384 and morphological disparity was similar to today’s.(6)Andrew M. Bush et al. (2007) “Changes in theoretical ecospace utilization in marine fossil assemblages between the mid-Paleozoic and late Cenozoic” Paleobiology, Volume 33, Page 76

Earth 470 Million Years Ago

Earth 470 Million Years Ago

The Ordovician Period existed between 485 and 443 million years ago, and was a time that most of Earth’s current classes and lower-level taxa of animals appeared in the fossil record. The oldest known fossilized plants also date to the Ordovician Period, and it is generally believed that they covered coastal regions of the ancient continents of Gondwana, Laurentia, Baltica, and Avalonia. The earliest fungi to colonize the surface of the continents played a crucial role in facilitating the colonization of land by plants through mycorrhizal symbiosis, which makes mineral nutrients available to plant cells. Fossilized fungal hyphae and spores from the Ordovician have been found dating back to about 460 million years ago, a time when the land plants most likely only non-vascular bryophytes.(7)Dirk Redecker et al. (2000) “Glomalean fungi from the Ordovician” Science, Volume 289, Number 5486, Pages 1920–1921

It is possible that the GOBE was caused by the establishment of an extraterrestrial agricultural colony, however this is not a requirement; evolution could have accomplished the same. The one unique thing that appeared during the GOBE that was missing from the Cambrian Explosion was the presence of terrestrial plants, mosses, and fungi. It is possible that these were planted as part of an agricultural colony, however it is also possible they evolved from sea-mosses. If this was a point of alien intervention, then these aliens appear to have been either amphibious or terrestrial.

Pterygotus

Pterygotus

These early terrestrial plants, mosses, and fungi seem to have reduced the carbon-dioxide levels of the atmosphere(8)Timothy M. Lenton et al. (2012) “First plants cooled the Ordovician” Nature Geoscience, Volume 5, Pages 86–89 causing an ice age at the end of the Ordovician Period. Gondwana had started the period in equatorial latitudes and as the period progressed drifted toward the South Pole. As it approached the Antarctic region it began to glaciate, and eventually the large continent was mostly covered in glaciers. This amplified the effects of the onsetting ice-age that led to some of the coldest global temperatures in the past 600 million years.

This ice age was part of the Ordovician–Silurian extinction events, which was collectively the second-largest of the five major extinction events in Earth’s existence in terms of percentage of species that went extinct, and second largest in overall loss of life. They happened between 450 to 440 million years ago, and constitute two pulses of extinction, separated by one million years.(9)Ricard V Solé and Mark Newman (2002) “Extinctions and Biodiversity in the Fossil Record – Volume Two, The earth system: biological and ecological dimensions of global environment change” Encyclopedia of Global Environmental Change Pages 297-391 They were the second biggest extinction of marine life, ranking below only the Permian–Triassic extinction event. More than 60% of marine invertebrates died(10)Peter M Sheehan (2003) “The Late Ordovician Mass Extinction” Annual Review of Earth and Planetary Sciences Volume 29, Pages 331-364 including two-thirds of all brachiopod and bryozoan families. Brachiopods, bivalves, echinoderms, bryozoans and corals were particularly badly affected. One of the causes of extinction events appears to have been the movement of Gondwana into the south polar region. This increased global cooling, glaciation, and consequently sea level fell worldwide. The falling sea level disrupted or destroyed habitats along the continental shelves. Evidence for the glaciation was found through deposits in the Sahara Desert. A combination of lowering of sea level and glacially driven cooling are likely primary causes for the Ordovician mass extinction.

Giant Orthocone

Giant Orthocone

In 2005 researchers at NASA and the University of Kansas produced a study indicating the Ordovician–Silurian extinction events could have been triggered by a star explosion called a gamma-ray burst. The scientists calculated that gamma-ray radiation from a relatively nearby star explosion, hitting the Earth for only ten seconds, could deplete up to half of the atmosphere’s protective ozone layer. Recovery would take at least five years. With the ozone layer damaged, ultraviolet radiation from the Sun would kill most of the life on the land and near the surface of the oceans and lakes, disrupting the food chain. Gamma-ray bursts in the Milky Way galaxy are rare, but the scientists estimate that at least one hit the Earth in the past billion years.(11)Christopher Wanjek (2005) Explosions in Space May Have Initiated Ancient Extinction on Earth NASA Goddard Space Flight Center

Through the Late Ordovician out-gassing from major volcanism was balanced by heavy weathering of the uplifting Appalachian Mountains, which sequestered carbon-dioxide.(12)Seth A. Young et al. (2009) “A major drop in seawater 87Sr/86Sr during the Middle Ordovician (Darriwilian): Links to volcanism and climate?” Geology, Volume 37, Number 10, Pages 951–954 In the Hirnantian Stage the volcanism ceased, and the continued weathering caused a significant and rapid draw down of carbon-dioxide. This coincides with the rapid and short ice age. The end of the second event occurred when melting glaciers caused the sea level to rise and stabilize once more. The rebound of life’s diversity with the sustained re-flooding of continental shelves at the onset of the Silurian Period saw increased biodiversity within the surviving species.

References   [ + ]

1. Axel Munnecke et al. (2010). “Ordovician and Silurian sea-water chemistry, sea level, and climate: A synopsis” Palaeogeography, Palaeoclimatology, Palaeoecology, Volume 296, Number 3–4, Pages 389–413
2. Thomas Servais et al. (2010) “The Great Ordovician Biodiversification Event (GOBE): the palaeoecological dimension” Palaeogeography, Palaeoclimatology, Palaeoecology, Volume 294, Number 3–4, Page 99
3. Thomas Servais et al. (2008) “The Ordovician Biodiversification: revolution in the oceanic trophic chain” Lethaia, Volume 41, Number 2, Page 99
4. Mary L. Droser and Seth Finnegan (2003) “The Ordovician Radiation: A Follow-up to the Cambrian Explosion?” Integrative and Comparative Biology, Volume 43, Page 178
5. Charles R. Marshall (2006) “Explaining the Cambrian “explosion” of Animals” Annual Review of Earth and Planetary Sciences, Volume 34, Pages 355–384
6. Andrew M. Bush et al. (2007) “Changes in theoretical ecospace utilization in marine fossil assemblages between the mid-Paleozoic and late Cenozoic” Paleobiology, Volume 33, Page 76
7. Dirk Redecker et al. (2000) “Glomalean fungi from the Ordovician” Science, Volume 289, Number 5486, Pages 1920–1921
8. Timothy M. Lenton et al. (2012) “First plants cooled the Ordovician” Nature Geoscience, Volume 5, Pages 86–89
9. Ricard V Solé and Mark Newman (2002) “Extinctions and Biodiversity in the Fossil Record – Volume Two, The earth system: biological and ecological dimensions of global environment change” Encyclopedia of Global Environmental Change Pages 297-391
10. Peter M Sheehan (2003) “The Late Ordovician Mass Extinction” Annual Review of Earth and Planetary Sciences Volume 29, Pages 331-364
11. Christopher Wanjek (2005) Explosions in Space May Have Initiated Ancient Extinction on Earth NASA Goddard Space Flight Center
12. Seth A. Young et al. (2009) “A major drop in seawater 87Sr/86Sr during the Middle Ordovician (Darriwilian): Links to volcanism and climate?” Geology, Volume 37, Number 10, Pages 951–954