Final answer:
The Cambrian explosion, a major diversification of life approximately 542 million years ago, is explained by theories involving environmental changes, such as increased oxygen and calcium levels, and genetic developments, notably the evolution of Hox genes. Ecological changes and the aftermath of a mass extinction may also have played roles. This event is fundamental to the diversity of modern animal phyla.
Step-by-step explanation:
Theories Explaining the Cambrian Explosion
The Cambrian explosion refers to the relatively short period of time in Earth's history, roughly 542 million years ago, when there was a rapid diversification of multicellular life. Two predominant theories attempt to elucidate this phenomenon:
- Environmental changes such as a rise in atmospheric oxygen and in oceanic calcium levels, creating conditions conducive to complex life.
- Genetic developments, including the evolution of Hox control genes, which increased the morphological complexity of organisms.
Additional factors might involve ecological relations, as predator-prey dynamics and competition could have stimulated diversification. Moreover, the prior mass extinction at the close of the Precambrian may have cleared the ecological slate, allowing new life forms to emerge and evolve rapidly. The combination of these theories suggests that the Cambrian explosion was likely a multi-causal event, involving intricate interactions between environmental, genetic, and ecological factors.
Following the Precambrian mass extinction, primitive animals like sponges and a diverse array of trilobites became abundant. This period of rapid diversification has left a lasting impact on the biodiversity we see today, with many modern animal phyla tracing their origins back to the Cambrian.