Question

The Cambrian explosion happened about 542 million years ago.

• What was the main significance of the twenty million years or so that they call the Cambrian explosion?
• Experts think that this explosion happened because of an "evolutionary arms race," once some animals evolved protective shells or exoskeletons. Describe what they mean by "evolutionary arms race".
• For protective shells or exoskeletons to evolve, there must first have been a "new" version of a gene that helped animals make these protective coverings. How did that "new" version of a gene arise?
• How did that new version of a gene for, say, an exoskeleton then become more common in the population?

Answer 1

The Cambrian explosion or Cambrian radiation was an event approximately 540 million years ago in the Cambrian period when practically all major animal phyla started appearing in the fossil record. It lasted for about 13 – 25 million years and resulted in the divergence of most modern metazoan phyla.The Cambrian explosion, as it is called, produced arthropods with legs and compound eyes, worms with feathery gills and swift predators that could crush prey in tooth-rimmed jaws. Biologists have argued for decades over what ignited this evolutionary burst.Some think that a steep rise in oxygen sparked the change, whereas others say that it sprang from the development of some key evolutionary innovation, such as vision.

The Cambrian Period marks an important point in the history of life on Earth. It is the time when most of the major groups of animals first appear in the fossil record. This event is sometimes called the "Cambrian Explosion," because of the relatively short time over which this diversity of forms appears.It was once thought that Cambrian rocks contained the first and oldest fossil animals, but these are now found in the earlier Ediacaran (Vendian) strata.

A lot can happen in 40 million years, the approximate length of the Cambrian Period. Animals showed dramatic diversification during this period of Earth's history. This has been called the "Cambrian Explosion". When the fossil record is scrutinized closely, it turns out that the fastest growth in the number of major new animal groups took place during the second and third stages (generally known as the Tommotian and Atdabanian stages) of the early Cambrian which are un named yet, a period of about 13 million years. 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.

Some scientists described the “explosion” as an evolutionary arms race, a period in which the evolutionary process; the diversification of organisms accelerated from 0 to 60 in a “relative blink.” An arms race between predator and prey have been commenced . A modest increase in oxygen levels enabled the evolution of predacious lifestyles, which in turn sparked an evolutionary arms race.In evolutionary biology, a process in which two or more lineages coevolve such that each, in turn, evolves more and more extreme/efficient defenses and weapons in response to the other parties' evolution is called an evolutionary arms race.

Arthropods are defined by the presence of an exoskeleton. Exoskeletons resemble armor, protecting the organism’s delicate internal organs from danger. From lobsters to ants to scorpions, the phylum Arthropoda displays incredible diversity. Most species of arthropods first appeared during the Cambrian Explosion, a period of rapid evolution about 550 million years ago. Dependence on fossilized skeletons also significantly limits the understanding of evolution. Only the parts of organisms that were already mineralized are usually preserved, such as the shells of molluscs. It helps that exoskeletons often contain "muscle scars", marks where muscles have been attached to the exoskeleton, which may allow the reconstruction of much of an organism's internal parts from its exoskeleton alone.

It is certainly no accident that insects are the most abundant and most diverse group of organisms on earth. They have maintained a position of ecological pre-eminence for over 400 million years: they have witnessed the rise and fall of dinosaurs; they have survived at least four major cataclysms that resulted in planet-wide extinctions; and they continue to thrive despite mankind's best efforts at eradication. While no single ecological or physiological attribute can account for this unparalleled success, the insects do have a unique combination of characteristics which, as a whole, have given them an unusual survival advantage. In brief, these attributes include an exoskeleton, small body size, the ability to fly, a high reproductive potential, complete metamorphosis, and adaptability in an ever-changing environment. As a "suit of armor", the exoskeleton can resist both physical and chemical attack.