When it comes to geological history
The biggest one of the biological radiation events,
What do you first think of?
(Source: Baidu Encyclopedia)
Congratulations you wrong.
The largest single biological radiation event is the
Ordovician biological radiation event
(The Great Ordovician Biodiversification Event, referred to as GOBE )!
The Ordovician biological radiation events are from the beginning of the Ordovician, and even the late Cambrian, Ordovician late marine biodiversity of large radiation events.
Cambrian eruption is a milestone in the history of the Earth’s life because it achieves a wide range of biological categories from ever-changing, modern almost all animals and plants Of the ancestors are present at this time.
However, the Cambrian ocean is still desolate, because each new class of creatures are only a small number of species, and the shape is relatively simple.
really make the ocean become bustling, is the Ordovician biological radiation events. Ordovician followed the Cambrian, began at 485.4 million years ago, ending at 443.8 million years ago, before and after lasted about 42 million years.
Ordovician biological radiation events almost throughout the Ordovician, is a very long time, the scale is very large “event”.
Ordinary biological radiation events, the lower taxonomic units (head, branch, genus and species level) a large number of diversity, marine life abundance and differentiation reached a peak,
The degree of differentiation is almost three times that of Cambrian
After the Ordovician, the whole Paleozoic in most of the time, marine biodiversity are living in such a high position.
In addition, the activities of new life have become stronger, they are no longer satisfied with the “only play in the sea floor mud”, but to the wider waters into the different depths of the ocean, Have appeared in life activities. The whole ocean has become lively.
With the advent of the Ordovician biological radiation events, ocean hegemony began to change hands.
Ordovician marine dominant cephalopods
In the Cambrian, standing at the top of the food chain, dominating the ocean is known as the shrimp.
At the end of Cambrian, the shrimp is gradually declining, replaced by faster swim, larger, meat-eating cephalopods, such as Orthoceras, the descendants of these cephalopods Is the octopus in the modern oceans, squid, nautilus, they also with super swimming and predation capacity to occupy a place where the sea overlord.
Right angle stone (Photo from Wikipedia)
Why does the Ordovician biological radiation event happen? Unlike the biological extinction, the Ordovician biological radiation events are not caused by significant or dramatic changes in the Earth’s environment, nor are they led by a single factor. It is a long process, a variety of biological environment factors of the complex process of interaction.
The scientists are still discussing the following reasons:
Billion years of history in a long time will be together, for a long time will be points. In the 1.1 million years ago the archaeological period, most of the land on the earth into one, forming a called Rodinia (Rodinia) of the supercontinent. The supercontinent began to disintegrate from about 750 million years ago. To the 480 million years ago, the Ordovician, it is Rodinia supercontinent torn apart, plate activity is very intense period. So what is the connection between the mainland’s diversity and the diversity of the creature?
In fact, the link between continental fragmentation and biodiversity is very complex. Early in 1972, some scholars have found that: super-continental cracking is corresponding to the increase in biodiversity, on the contrary, the formation of the supercontinent corresponds to the reduction of biodiversity.
That is, when the earth on the block polymerization, the earth’s biology are also tend to “world Datong”, and when the supercontinent discrete, each block is inclined to breed the distinctive “tribe” The ecological community).
(The relationship between the supercontinent division and the biological diversity, followed by the descendants of the Rodinian continent, the Gondwana continent, the Panchia supercontinent. Source Servais et al., 2009)
Specifically, on the one hand, the supercontinent disintegrated into a large number of islands and land blocks, these islands and blocks gradually away from, for the biological species to create the conditions.
Exotic species is the most classic species formation:
was originally the same species, geographically isolated, can not communicate with each other, in different environments gradually evolved into different Of the species.
Give a typical example: Dear Darwin’s grandfather went to the Galapagos Islands, found that different islands on the bird’s beak are not the same hey! For example, Australia and New Zealand, on these two separate land to produce a lot of unique species.
On the other hand, when the mainland is disintegrated, a large amount of magma in the mantle gushes out and encounters air or sea water.
On the other hand, It will cool down. In the warm equatorial region, large areas of shallow sea area expansion, for the biological to provide more and more comfortable living environment. Finally, the continental crust is accompanied by frequent volcanic activity, volcanic eruption of a large number of volcanic ash, coupled with the newly formed mountains are weathered erosion, rock and mineral debris continue to be imported into the ocean. And many of these minerals are essential nutrients, which is equivalent to providing a lot of food for marine life, the number of biological naturally appeared explosive growth.
The volcanic activity also releases large amounts of carbon dioxide into the atmosphere.
At the end of the Cambrian, at the beginning of the Ordovician, the earth’s carbon dioxide concentration is about 15 times that of the modern atmosphere.
It can be said that the Ordovician Earth is a large greenhouse!
(Carbon dioxide concentration changes, source https://phys.org/news/)
The greenhouse effect has exacerbated the trend of sea-level rise.
sea level is the highest, even higher than the modern sea level above 200 meters! Shallow sea area so enlarged, which provides a place for the prosperity of the creatures.
At the same time, the Ordovician gradually cool the sea also make the living conditions of marine life better.
Volcanic activity emitted a large number of volcanic ash obscured the sun, coupled with the basalt weathering, so that the sea to cool. Studies have suggested that the Ordovician seawater temperature in the early Ordovician period even more than 40 ℃, until the Middle Ordovician period dropped to 28-32 ℃.
It is precisely because in the early Ordovician earth is too hot, not suitable for a large number of biological breeding, so later the sea cold, which makes the marine life can be happy to reproduce, evolve, resulting in the Ordovician biological radiation event.
The food chain revolution
And the modern ocean in the “big fish to eat small fish, small fish eat shrimp”, the Ordovician ocean in a variety of biological Also constitute a complex food chain and food network.
The bottom of the food chain is all kinds of algae and plankton. As mentioned earlier, the Ordovician plate movement and volcanic activity provide a broad living space for creatures and Adequate source of nutrition, making the ocean of small algae, zooplankton into explosive growth, similar to the current pollution of water cyanobacteria outbreak, but larger. And these small creatures become a food source of high-level creatures in the food chain, and thus provide a rich ecological space for the formation of species diversity.
The internal cause of the organism, such as the way of life, the tolerance to environmental change, the new body configuration , The appearance of tissues and organs, gene mutations, and so on.
Studies have found that the early Ordovician period,
bivalves (modern representatives such as oysters, clams, etc.) evolved out of the filter feeding gills.
This feature makes them more adaptable to the environment where the nutrients are increased, resulting in the diversity of bivalve species.
Source: http: // newsIn addition to the above factors, there are mechanisms for the occurrence of biological events in Ordovician, as well as
stone impulse induced theory, chromosomal variation Theory
and so on.
I believe that one day we can link all the factors to better understand this remarkable biological radiation.
Thomas Servais et. al. (2010) The Great Ordovician Biodiversification Event (GOBE): The palaeoecological dimension Palaeogeography, Palaeoclimatology, Palaeoecology.
Thomas Servais et. al. (2008) The Ordovician Biodiversification: Revolution in the oceanic trophic chain. Lethaia.
Zhan Renbin et al., 2013, Ordovician Biological Radiation Research: Review and Prospect. Science Bulletin