About 500 million years ago, there was a relatively short time period, about 20 million years, in the planet's history where an explosion of innovation occurred. This period, called the Cambrian Explosion, saw the appearance of the first vision, the first hard skeletons, and the first predators, among other critical foundations of modern ecosystems.
Before the Cambrian Explosion, organisms were mostly simple. They included single-celled and small multicellular organisms with limited complexity. The fossil record from this time, specifically from the preceding Ediacaran Period, primarily shows soft-bodied organisms. However, the beginning of the Cambrian period saw a significant increase in the complexity and diversity of life forms.
There are several theories proposed to explain the causes of the Cambrian Explosion. One theory suggests that increases in oxygen levels in the Earth’s atmosphere and oceans enabled more complex metabolic processes necessary for more extensive and diverse organisms. Another theory points to the development of the genetic toolkit for building complex body plans, with genes regulating the growth of tissues and organs evolving rapidly during this time.
The truth is that we don’t know the actual reason, but what is clear is that evolution can run at different speeds. This period represents less than 0.5% of Earth's age, but it happened to be a time when huge changes occurred. It seems that the phrase “There are decades where nothing happens; and there are weeks where decades happen” also applies to evolution.
Craving more? Check out the source behind this Brain Snack!
