Their most common line is that the leap of evolution during the Cambrian involved too many changes too quickly, that the Cambrian therefore represents a gap in the fossil record best filled by a supernatural explanation.
There is obviously a tremendous gap between one-celled microorganisms and the high complexity and variety of the many invertebrate phyla of the Cambrian. If the former evolved into the latter, it seems impossible that no transitional forms between any of them would ever be preserved or found.
A much more likely explanation for these gaps is that they represent permanent gaps between created kinds. Each organism has its own structure, specifically designed for its own purpose, not accidentally evolved by random processes.
IDC became a safe front for creationists to espouse scientific terminology while repeating religiously-motivated attacks on evolution. Creationist rhetoric has changed, but their indignation toward the Cambrian explosion is the same. Nearly all the animal phyla appear in the rocks of this period, without a trace of the evolutionary ancestors that Darwinists require. Why are creationists so obsessed with this aspect of paleontology, and not, say, the fascinating fossil record of sloths?
What special appeal does the Cambrian explosion have for them? Right there: creation. The ancient lineages that eventually diversified extend far back in time, a long fuse leading to the eventual explosion.
While the rapid evolution during the Cambrian is described as geologically brief, it is important to define what that means. On human timescales, the shortest estimation for the length of the Cambrian explosion, about 10 million years, is incomprehensibly long. Moreover, the tiny Cambrian arthropods likely had much faster maturations and much shorter lifespans than humans. Our anthropocentric perception of the flow of time, in which a family might have only three or four generations per century, is very different from the number of generations Cambrian critters produced.
Ten million years provides plentiful time, as Lee et al. Then the Nama biota—a so-called wormworld that ushered in tubular animals, including some with hard shells. When the Cambrian fauna eventually arrived, Wood thinks it appeared in two pulses. That makes at least five distinct bursts of diversification that straddle the divide between the periods.
Did only a few Ediacaran lineages survive the transition to the Cambrian, or did many of them do so? Lidya Tarhan from Yale University is more convinced. Others have argued that the Cambrian explosion was sparked by a rise in oxygen , which fueled the evolution of active behaviors and larger, gas-guzzling bodies. Instead, for much of the Ediacaran, levels of the vital gas fluctuated over time, and across different layers of the oceans.
Read: Earthquakes and volcanoes may have helped intelligent life evolve. One of the earliest known groups of arthropods the phylum which includes all modern-day insects, arachnids and crustaceans , trilobites were wildly successful in the ancient oceans, with some 20, species spread over ten orders.
They're also known from their extensive fossil record. But their evolution is something of a mystery. At one point during the Cambrian Period, trilobites suddenly went from being soft-bodied animals to developing hard shells.
And they were rapidly found in shallow seas all around the world. Greg explains, 'There is a certain point at about million years ago when you start to get trilobite body fossils in different parts of the world. What happened to allow this sudden shift has long been debated. It is thought that something changed in the chemistry of the oceans at around this point in time, allowing soft-bodied animals such as early trilobites and echinoderms to suddenly be able to build solid biomineralised shells, but that isn't the whole story.
That is what we wanted to test. The Cambrian explosion, considered a crucial event in the evolution of animals, was in full burst by million years ago. There is no one aspect that can be held up as the cause of this period of rapid evolution, but it is best viewed more as a swirling together of factors. It was around this time that massive amounts of nutrients that had eroded from continental rocks on land were washed into the oceans, providing the calcium and phosphorus needed to build skeletons and hard shells.
Animals start burrowing into the sediment, aerating beneath the seafloor and stirring these nutrients up. This helped plankton take off in a big way, which in turn formed the basis of ever more complex food webs, ushering in the first major predators. This gives us a better understanding of which animals were eating each other. These environmental changes were combined with changes in the development of animals, where new genes that regulate body patterning and segmentation appear.
Hard exoskeletons, jointed legs and compound eyes emerged during this time in organism. Animals also evolved some of the earliest biting jaws, as well as antennae, during the time period. Researchers have long debated exactly how animals could have evolved so quickly during the period. Creationists have even used the Cambrian explosion to raise doubts about the theory of evolution, suggesting some divine hand must have played a role. So the team tallied anatomic and genetic differences between living creatures and then used dates from the fossil record to estimate how fast evolution proceeded, or how quickly those changes came about.
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