The Silurian (443.7 to 416.0 million years ago)* was a time when the Earth underwent considerable changes that had important repercussions for the environment and life within it. One result of these changes was the melting of large glacial formations. This contributed to a substantial rise in the levels of the major seas. The Silurian witnessed a relative stabilization of the Earth's general climate, ending the previous pattern of erratic climatic fluctuations.

Coral reefs made their first appearance during this time, and the Silurian was also a remarkable time in the evolution of fishes. Not only does this time period mark the wide and rapid spread of jawless fish, but also the highly significant appearances of both the first known freshwater fish as well as the first fish with jaws. It is also at this time that our first good evidence of life on land is preserved, such as relatives of spiders and centipedes, and also the earliest fossils of vascular plants.

Life

The Silurian is a time when many biologically significant events occurred. In the oceans, there was a widespread radiation of crinoids, a continued proliferation and expansion of the brachiopods, and the oldest known fossils of coral reefs. As mentioned earlier, this time period also marks the wide and rapid spread of jawless fish, along with the important appearances of both the first known freshwater fish and the appearance of jawed fish. Other marine fossils commonly found throughout the Silurian record include trilobites, graptolites, conodonts, corals, stromatoporoids, and mollusks.

It is also in the Silurian that we find the first clear evidence of life on land. While it is possible that plants and animals first moved onto the land in the Ordovician, fossils of terrestrial life from that period are fragmentary and difficult to interpret. Silurian strata have provided likely ascomycete fossils (a group of fungi), as well as remains of the first arachnids and centipedes.

Perhaps most striking of all biological events in the Silurian was the evolution of vascular plants, which have been the basis of terrestrial ecology since their appearance. Most Silurian plant fossils have been assigned to the genus Cooksonia, a collection of branching-stemmed plants which produced sporangia at their tips. None of these plants had leaves, and some appear to have lacked vascular tissue. Also from the Silurian of Australia comes a controversial fossil of Baragwanathia, a lycophyte. If such a complex plant with leaves and a fully-developed vascular system was present by this time, then surely plants must have been around already by the Ordovician. In any event, the Silurian was a time for important events in the history of evolution, including many "firsts," that would prove highly consequential for the future of life on Earth.

Tectonics and paleoclimate

Although there were no major periods of volcanism during the Silurian, the period is marked by major orogenic events in eastern North America and in northwestern Europe (the Caledonian Orogeny), resulting in the formation of the mountain chains there. The ocean basins between the regions known as Laurentia (North America and Greenland), Baltica (central and northern Europe and Scandinavia) and Avalonia (western Europe) closed substantially, continuing a geologic trend that had begun much earlier. The modern Philippine Islands were near the Arctic Circle, while Australia and Scandinavia resided in the tropics; South America and Africa were over the South Pole. While not characterized by dramatic tectonic activity, the Silurian world experienced gradual continental changes that would be the basis for greater global consequences in the future, such as those that created terrestrial ecosystems. A deglaciation and rise in sea levels created many new marine habitats, providing the framework for significant biological events in the evolution of life. Coral reefs, for example, made their first appearance in the fossil record during this time.

The Silurian Period's condition of low continental elevations with a high global stand in sea level can be strongly distinguished from the present-day environment. This is a result of the flood of 65% of the shallow seas in North America during the Llandovery and Wenlock times. The shallow seas ranged from tropical to subtropical in climate. Coral mound reefs with associated carbonate sediments were common in the shallow seas. Due to reduced circulation during the Ludlow and Pridoli times, the process of deposition of evaporites (salts) was set in motion. Some of these deposits are found in northern Europe, Siberia, South China and Australia.

The Complete History of the Earth: Silurian Period :hex-crab:

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  • spectre [he/him]
    ·
    2 years ago

    Weren't some pirates basically lifestylist anarchists? Thought I saw like a "pirate's code" a few years back that was almost kinda good in some ways

    • Frank [he/him, he/him]
      ·
      2 years ago

      It's really, really complicated because there was a huge range of ideologies and beliefs among pirates, and a lot of them were just "Steal a bunch of shit so I can buy slaves and a plantation in America".

      But a few pirate groups undertook radical experiments in direct democracy, directly and violently opposed slavery, fought against what they perceived as an unjust society, or just did their best to destroy British shipping. One of the most common reasons people went pirate were the absolutely horrific conditions on merchant and navy ships of the time, where sailors were sometimes violently kidnapped and essentially enslaved, subjected to horrible conditions including disease, bad food, isolation at sea, and frequent disciplinary torture.

      Being a pirate was a rough, dangerous, and nasty occupation that often ended in a violent death, but for many people serving on a Navy or merchant ship was worse and they took the opportunity to go pirate when it presented itself. I don't think it's too much of a stretch to say that pirates were no more immoral or unethical than contemporary "legitimate" shipping, and in some cases were clearly morally superior in their actions as they were simply stealing from colonial thieves and slavers instead of directly engaging in the slave trade and other contemporary horrors.

      That said, pirates shouldn't be overly romanticized. Many were happy to engage in the slave trade or were rich men who bought a ship and used it to prey on people weaker than them. Many engaged in all sorts of violence and bloodshed.

      • spectre [he/him]
        ·
        2 years ago

        Thanks for filling all that in comrade, it's been a long ass time since I've seen the "are pirates anarchist?" discussion, would have been back on the old sub or r/C@