In the previous article, we introduced the Paleozoic era, now it is time to talk about its first period- the Cambrian. It was the time of the biggest revolution in Earth’s biodiversity, the breakup of the super-continent, and the mass extinction. Let’s take a closer look at the events of the period.
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The Cambrian Explosion
Despite many complex studies, the origin of the Cambrian explosion remains a mystery. The first hypothesis suggest it started due to the melting of ice covering our planet. Secondly, there are theories that relate the revolution to complex body plans or ecological relations between organisms. And finally, the most recent theory suggests the event was triggered by the movement of plate tectonics. Whatever started the 25-million-years event, it led to the appearance of most phylum we know today. The ongoing war between prey and hunters began, leading to the development of complex ecological relations. Moreover, organisms started leading various lifestyles, which led to the development of specialized organs. Lastly, at the end of the event first animals left the oceans and stepped on land.
The End of Cambrian- Mass Extinction
The flourishing life of the Cambrian explosion creates a beautiful vision. However, it couldn’t last forever, and the end of the period is marked with an extinction event. Although it was not the biggest in Earth’s history, it wiped out the conodonts (they appeared again in the Ordovician), and killed a lot of trilobites. We still don’t know how it happened. Most hypotheses focus on probable glaciation and covering oceans with basalt lava. However, there’s a lot of controversy around it, up to the point when some scientists question if it even happened. The explanation is the gap in evidence material, that was interpreted as extinction, despite good conditions. To know the exact order of events we need more studies on the matter. Despite that, we can for sure say, that something about 485.4 million years ago marked the end of the Cambrian period and the beginning of the Ordovician.
Changes On Earth
Climate during most of the period was very hospitable for life. In the beginning, the temperature raised, to 7 degrees higher than today. With passing time Earth recovered from glaciation, which led to ice melting. As a result, the water levels raised, which continued through the Ordovician period. On the continental site, first, the formation of supercontinent Gondwana changed how the lands looked. Afterward, three big landmasses separated from the main continent and drifted north. Due to rising sea levels, some land was covered with water, and the ocean took more space than it does today. Plate tectonics movement might have triggered the Cambrian explosion, so could rising sea levels, or rise in oxygen levels. During the period oxygen took 12.5% of Earth’s atmosphere (21% today). All of those changes in Earth’s climate and geology had an effect on life, some big change probably led to the mass extinction.
The conclusion that most phyla appeared during the explosion event didn’t come from anywhere. It was a conclusion of the fact, that the oldest fossils of most phyla are from that time. The beginning of the period was marked with the appearance of the burrow of an animal and the oldest complex trace fossil. Other evidence includes microbial mats, stromatolites, and of course trilobites. Especially interesting among them is a fossil of Anomalocaris. It was found by the team from Yale University in 2011 in Morocco. The animal was probably the biggest predator of its time. All the evidence led scientists to the conclusion, that during the Cambrian period organisms established body plans familiar today. It also enables studying life cycles and the development of past organisms. Finally, there are some complex biogeochemical models simulating the atmosphere of the period, helping to understand the relations between conditions and organisms.
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