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5195
From: Sciguy, [DNS_Address]
Subject: What Caused the Cambrian Explosion? NT
URL: Link
5199
From: Akira, [DNS_Address]
Subject: also, the Cambrian period existed between 2 ice ages
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this article gives several good reasons for the explosion of life during the Cambrian era. The environment was more hospitable to life, especially with the emergence of increasing oxygen levels in oceans, where the ‘explosion’ occurred. excerpt: “The Cambrian follows the Ediacaran Period, during which time the continents had been joined in a single supercontinent called Rodinia (from the Russian word for "homeland", rodina). As the Cambrian began, Rodinia began to fragment into smaller continents, which did not always correspond to the ones we see today. The reconstruction above shows the rifting of Rodinia during the second stage (Tommotian) of the Cambrian . Green represents land above water at this time, red indicates mountains, light blue indicates shallow seas of the continental shelves, and dark blue denotes the deep ocean basins. (For clarity, the outlines of present-day continents have been superimposed on the map.) World climates were mild; there was no glaciation. Landmasses were scattered as a result of the fragmentation of the supercontinent Rodinia that had existed in the late Proterozoic. Most of North America lay in warm southern tropical and temperate latitudes, which supported the growth of extensive shallow-water archaeocyathid reefs all through the early Cambrian. Siberia, which also supported abundant reefs, was a separate continent due east of North America. Baltica — what is now Scandinavia, eastern Europe, and European Russia — lay to the south. Most of the rest of the continents were joined together in the supercontinent Gondwana, depicted on the right side of the map; South America, Africa, Antarctica, India, and Australia are all visible. What is now China and east Asia was fragmented at the time, with the fragments visible north and west of Australia. Western Europe was also in pieces, with most of them lying northwest of what is now the north African coastline. The present-day southeastern United States are visible wedged between South America and Africa; they did not become part of North America for another 300 million years. Tectonism affected regions of Gondwana, primarily in what are now Australia, Antarctica, and Argentina. The continental plate movement and collisions during this period generated pressure and heat, resulting in the folding, faulting, and crumpling of rock and the formation of large mountain ranges. The Cambrian world was bracketed between two ice ages, one during the late Proterozoic and the other during the Ordovician. During these ice ages, the decrease in global temperature led to mass extinctions. Cooler conditions eliminated many warm water species, and glaciation lowered global sea level. However, during the Cambrian there was no significant ice formation. None of the continents were located at the poles so land temperatures remained mild. In fact, global climate was probably warmer and more uniform than it is today. With the retreat of Proterozoic ice, the sea level rose significantly. Lowland areas such as Baltica were flooded and much of the world was covered by epeiric seas. This event opened up new habitats where marine invertebrates, such as trilobites, radiated and flourished. Plants had not yet evolved, and the terrestrial world was devoid of vegetation and inhospitable to life as we know it. Photosynthesis and primary production were the monopoly of bacteria and algal protists that populated the world's shallow seas. Also during the Cambrian, the oceans became oxygenated. Although there was plentiful atmospheric oxygen by the beginning of the period, it wasn't until the Cambrian that there was a sufficient reduction in the number of oxygen-depleting bacteria to permit higher oxygen levels in the waters. This dissolved oxygen may have triggered the "Cambrian Explosion" — when most of the major groups of animals, especially those with hard shells, first appeared in the fossil record." |
5200
From: Sciguy, [DNS_Address]
Subject: “…Here’s looking at you, kid.”
URL: Casablanca
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“Of all the gin joints, in all the towns, in all the world, she walks into mine…” “Welcome back to the fight. This time I know our side will win.” Ok Akira, (I like the sound of that), I'm taking a long break. Sappy exit, but I'm tired of sadistic trolls, ego-addled morons, brain-dead pseudoscientists, and non-thinking bible thumpers. What the heck are you and Snodrop doing in a place like this? |
Responses:
[5202]
5202
From: BJ, [DNS_Address]
Subject: Re: “…Here’s looking at you, kid.”
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Don't be so tough on yourself. Your projection tells much about you. |
Responses:
None
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