Cambrian

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The Cambrian was the first period of the Paleozoic era and the Phanerozoic Eon on the Geologic timeline,^[1] lasting from 541 million years ago to 485 million years ago, with a million year margin of error, give or take. The Cambrian marked an "explosion" of biodiversity; indeed, almost all of today's phyla evolving during the Cambrian period, and evolution was going EVERYWHERE.^[2] This compounded with the comparatively poor record of Precambrian life has given many misinformed people the idea that life sprung out of nothing.^[3] In spite of all this manufactroversy, the Cambrian still holds an important place in Earth's natural history.

Paleogeography[edit]

The supercontinent of Pannotia just a few million years before the start of the Cambrian.

The Cambrian started with the breakup of the supercontinent Pannotia, the eighth supercontinent in the history of planet Earth.^[4] Relatively short-lived, this landmass was centered in the southern hemisphere. Over the course of the Cambrian period, Pannotia broke up. These were the subcontinents of Laurentia (Most of modern North America),^[5] Baltica (modern day Northwestern Eurasia),^[6] and Siberia (Guess what that is today).^[7] These continents were slowly drifting north.

The sea levels were higher than they are today, which provided large amounts of warm, shallow seas, a perfect cradle for the Cambrian explosion to take place. Though the climate was warmer than it was today,^[8] fluctuating sea levels indicate the possibility of "ice ages".^[9]

Life[edit]

The Cambrian saw the emergence of most modern phylum though in primitive forms.^[10] The Arthropods were the most diverse and for many years Trilobites were considered the king among them in terms of numbers.^[11] The Cambrian saw their peak diversity in form and lifestyle with species ranging from tiny blind burrowers,^[12] to massive predators.^[13] They coexisted with many other arthropods including the first large predator Anomalocaris which was a terrifying 1 meter in size.^[14]

The earliest chordates such as Pikaia, Haikouichthys, and Myllokunmingia were also present. The diversity indicates that chordates are an ancient group. Their small stature at the time limited them to minor roles in the Cambrian.^[15]

The unique Cambrian fauna is believed to have been the direct cause of the disappearance of Ediacaran life.^[16] Ironically it was short lived in of itself being replaced in the Ordovician with the marine fauna that would dominate for the rest of the Paleozoic. This turnover event is called the Cambrian-Ordovician extinction event and is the divide between it and the next period, the Ordovician.^[17]

Common Cambrian misconceptions[edit]

Many misconceptions surround the Cambrian time period. One of the major misconceptions is that everything just spontaneously generated in the Cambrian explosion.^[18] This is not true on several fronts. Unicellular bacteria and archaea both emerged long before the Cambrian, emerging at least 4 billion years ago.^[19] There is also the discovery of various Precambrian rocks which have strange multi-cellular organisms.^[20] Although strata this old is rare it has been found in Canada,^[21] South Australia,^[22] and Namibia.^[23] Even if the focus is just on animals several animal phylum emerged prior to the Cambrian including sponges,^[24] jellyfish, and comb jellies.^[25] At least one hard-bodied animal, Cloudina, lived a few million years before the start of the Cambrian,^[26] although the amount of shelled organisms would explode during the Cambrian, with the shelled organisms being much more likely to be preserved than the soft-bodied animals like worms and jellyfish that came before them. There is also evidence of other phyla emerging prior to the Cambrian but the evidence is inconclusive.

Now to be fair to both sides, scientists themselves have made many mistakes regarding Cambrian life. The most famous of these blunders is the former belief that Anamalocaris was in fact two separate animals, a shrimp tail and a jellyfish.^[27]

References[edit]