The Cambrian period is one of the most important in the history of the Earth. It marks the point at which larger groups of animals begin to appear in fossils. This was a period of great evolutionary progress in which there was an explosion of diversity throughout all life on Earth. The Cambrian period lasted between 542 million and 488 million years.
It is believed that due to the breakup of the continent during the Cambrian period, the Earth was covered by several shallow seas. During the Proterozoic era, one supercontinent was known as Pannotia. The disintegration of this gigantic land mass allowed shallow seas and rivers to form between the land and the land. Cambrian climates were significantly warmer than at other places in Earth’s history and did not freeze. This lack of polar glaciation may help to account for the prevalence of shallow Welsh seas across the planet. Here there was no land of plants, and generally in the Welsh mainland there were barren places of rocks and sand.
Although the Cambrian period saw an explosion of evolution, the prevailing drama is played out in the oceans. When the continents were safe, all the major phyla made a firm appearance for the first time in this Eon. Oxygen that was released into the atmosphere when the Proterozoic began to dissolve from seaweed in the oceans. Anaerobic organisms generally have a greater chance to diversify with efficient use of oxygen. Anaerobic organisms tend to be much smaller, softer, and less diverse than aerobic organisms relative to the inefficiency of fermentation processes They use it to produce energy.
Life on Earth during the Cambrian period was mostly restricted to invertebrates, or animals that lacked spines. Echinoderms, which include the modern starfish, sea cucumbers and sand dollars, began to appear in the Cambrian sea. However, modern specimens had not yet evolved and many Cambrian echinoderms did not appear until later periods in Earth’s history. Cephalopods, which today include octopus and octopus, also began to colonize the seas, as did gastropods (snails and slugs). Although molluscs made their first appearance in the Cambrian period, they are still relatively rare compared to other marine organisms.
Arthropoda, the family that includes today’s insects and spiders, began to take hold in the Welsh seas. These organisms are known for their hard outer shells called exoskeletons that provide nature’s armor but also restrict growth. One of the most noble of the Welsh beasts, the trilobite, made its appearance in the shallow sea that covers the Earth. This particular arthropod is similar to a modern day bug with its segmented back and oval shape and is estimated to be about 50% of all marine species. However, trilobites are outmatched in size by arthropod predators known as anomalocarids. These predators could grow up to a meter in length, and they threw a pair of organs in their front to bring prey with their teeth arranged in their mouths.
The first vertebrates appeared in the Cambrian, although they were small, with mandibles that do not often appear in fossils. A tiny fish creature called the haikouichthys would form the basis for the development of bony and cartilaginous fish like sharks later down the road. Until the Ordovician Period, vertebrates took a long time to rise to the top of the evolutionary ladder.
