Hyper Evolution -

The Early Cambrian, a Game Changer

Prologue

We have traversed our way through the first four billion years of life on our planet as we explore our Forgotten Origins. The farther back in time we travel, the less factual evidence we find, meaning we fill in the gaps with speculation and theories. But the arrival of the Cambrian ushered more certainty into the geological record.

All We See

The start of the Cambrian Period 541 million years ago marked the point in time when mother nature was done with dawdling around. Evolution struggled for billions of years to produce single-celled bacteria and eukaryotes. They were an inauspicious start to the complex biosphere we enjoy today. Finally, in the Ediacaran, complex multi-celled creatures made their way onto the stage of life. But they were just the warmup act, and evolution went into hyperdrive with the arrival of the Cambrian.

Today we recognize 36 animal phyla, but nine major phyla contain most of the extant species in our biosphere — Mollusca, Porifera, Cnidaria, Platyhelminthes, Nematoda, Annelida, Arthropoda, Echinodermata, and Chordata. All these major phyla appeared in the fossil record during the early Cambrian. So after four billion years of struggling, the key branches of the animal kingdom evolved during a 10 to 15 million year period.

If we reduce Earth’s history to a single day, then all major branches of life appear during a five-minute interval at about 9:30 in the evening. It’s an extraordinary observation given our tendency to view evolution as a slow march over time, with life steadily moving toward increasing complexity.

The reality is that life exploded onto the scene during an incredibly short period of hyper evolution. Sponges of the Porifera phylum appear to be the single member of our modern major phyla with a definable history before the Cambrian explosion. Evolution is not a steady flow of rising excitement. Instead, it is long periods of boredom punctuated by brief episodes of frantic change.

Focus on Success

A focus on success defines evolution. Organisms best suited for the available ecological niches will thrive and come to dominate their ecosystem. We know of them because of their success. The greater the species population, the better its chance of preservation in the fossil record.

If we want to understand the winners in early Cambrian evolution, we should note the rise of trilobites. For 55 million years, these creatures dominated the Cambrian biosphere, making them one of biology’s great success stories. Their reign continued for another 230 million years after the end of the Cambrian, until their demise during the end Permian mass extinction — the Great Dying.

Trilobites had hard exoskeletons for protection and limbs for motion and predation. The closest modern-day analog is a horseshoe crab.

Their wild success was due to evolutionary innovations and species diversity. The term trilobite refers to a class of animals with over 20,000 different species. They ranged in size from under a millimeter to over several feet in length and adapted to a vast range of habitats.

It is said that in the land of the blind, the one-eyed man is king. Trilobites were early innovators in the field of vision, with some species developing enlarged eyes. Imagine two critters searching for the same dinner, and one can see it, but the other can’t. You get the picture.

When the available ecological niche required swimming, fast bullet-shaped swimmers appeared. But when burrowing was the ticket to survival, trilobite species evolved to live in the sea-bottom mud. Some lost their eyes because they spent all their time ‘underground.’

Trilobites possessed a key ingredient of success, evolutionary adaptability.

Life in the Cambrian

The Cambrian was a great time to be alive if you were a trilobite. Living on land was not an option, and life remained submerged below the ocean surface. Shallow marine environments were the hip place to be. There, you found sunlight and shallow water where oxygen from the atmosphere constantly seeped into the surface waters. These two combined benefits translated into ‘plenty of food.’

Earlier, in the Ediacaran, the Rodinia supercontinent broke apart, and by the mid-Cambrian, two large landmasses existed. The Gondwana supercontinent covered a large area near the South Pole, and Laurentia hovered closer to the equator. The shallow Cambrian seas along the continental shelves existed in the coldest and warmest areas on the planet. Adaptability was a must-have for species survival. But cold is a relative term.

Global temperatures were on the rise during the Cambrian. Previously, during the Neoproterozoic, Earth was in a deep freeze during the Cryogenian Period. The planet warmed during the Ediacaran, but average global temperatures at the beginning of the Cambrian were probably slightly lower than today. However, the Cambrian world kept warming, and the average global temperature throughout the Cambrian was 22 Celsius as opposed to our modern-day average of about 15 Celsius.

For context, Cambrian temperatures rose an average of 0.5 degrees C per million years. In the Anthropocene, we have managed to achieve about a 1 degree C rise in a mere 150 years. The world is unfortunately still on course towards Cambrian conditions. We are finding out the hard way that awareness of climate change is not enough. Action to mitigate global warming needs follow our newfound awareness.

(The Forgotten Origins series is also available on ArcheanWeb)