The secrets of Earth’s evolution revealed

An example of excellent fossil preservation of trilobites from the Cambrian Explosion.
An example of excellent fossil preservation of trilobites from the Cambrian Explosion.
An example of excellent fossil preservation of trilobites from the Cambrian Explosion.

Recently, Dr Timothy Raub of the University of St Andrews, joined other international scientists in a quest to hush the hot debate concerning the causation of Earth’s greatest evolutionary event – The Cambrian Explosion.

Approximately 520 million years ago, an unimaginable episode of accelerated evolution occurred in as few as 10 million years on Planet Earth. It was named the Cambrian Explosion, and has been the centre of dispute amongst scientists since Darwin.

One side of the argument focuses on the truth of the unprecedented event, whilst others argue it is a false artefact of an unreliable fossil archive. The research discusses the Cambrian Explosion as both an effect and an artefact of True Polar Wander (TPW), leading Dr Raub to conclude ‘the particular locations of Cambrian continents relative to each other was special in a way that supercharged animal speciation, while preserving an unusually good record of those early fossils.’ This suggests that both viewpoints were indeed correct.

Now, after publication, Dr Raub discusses his research and details an answer to the mysterious phenomenon.

I asked Dr Raub to summarise the main message of the breakthrough in order to simplify the complex science involved in the development,

“Everyone is familiar with the idea of slow continental drift. Every year Scotland and Greenland grow farther apart because the European and North American plates are spreading at the rate your hair grows. Fewer people have heard of a bizarre process called True Polar Wander, in which all of Earth’s plates lurch at once in the same direction, at a much faster speed.  Basically, during True Polar Wander, the whole solid Earth slips on the liquid-solid, core-mantle boundary.

“About 520 million years ago, in the early Cambrian Period, TPW lasting for 5-10 million years moved all the continents which had been previously located near the poles to the equator. For years, scientists have been debating whether this TPW event – or some other environmental trigger – caused the Cambrian Explosion of animal life when all of Earth’s modern bodyplans radiated from a smaller number of simpler ancestors.

“Our recent paper points out that early Cambrian TPW had to increase net biodiversity, precisely because it increased the area of continental shelves in Earth’s low-latitude biodiversity hotspots, while diminishing shelf area in polar biodiversity ‘deserts.’ This underlying Latitudinal Diversity Gradient is one of Earth’s most fundamental ecological patternings, and every student in the world probably learns it in their first class studying organismal biology.

“We also pointed out that other consequences of TPW, like sea level rising up onto continents moving toward the equator, would tend to promote allopatric speciation and lock in disparity within new lineages occupying previously barren niches.”

Despite this discovery and the confirmation of seemingly conflicting theorems, Dr Raub explains how this is not the end of the road for research surrounding the Cambrian Explosion, suggesting that the paper should not end the debate, but “reset it.” Like many other scientific conundrums, this research details the importance of reviewing the facts to create a conclusion. Dr Raub says: “Instead of different groups arguing that environmental conditions must drive evolution, or alternately that big-picture evolution is purely biological and ignores environment, we show that you cannot separate the two in the Cambrian. Another way of saying this is, Both sides were right!  Purely biological evolution was naturally pumped up because Cambrian TPW concentrated Earth’s landmasses at low latitude. And newly available shallow continental ecospace promoted speciation because of local and regional geochemical and environmental variability.”

Naturally, it is theorem and observation which leads to correct interpretations. Considering the work is not over in this case, I asked Dr Raub what the next steps would be for furthering this conclusion on the Cambrian Explosion.

“Our concept for the Cambrian Explosion must be tested over the coming years,” he says. “Verification is the acid test of science!  In particular, geologists will try to ever better date the rise of sea level in North America, Scotland, Africa, India, and China which we attribute to true polar wander. New data showing how the Scandinavian continent moved during the early Cambrian also can support, or disprove, our ideas. We are next planning to test whether the chemistry of Cambrian ocean water also changed at precisely the same time as the TPW event – if it did, then we think that underscores the profound effects of Cambrian true polar wander.”

The publishing of this research comes with much relief and great excitement to the science community as we wait for the future evolution of the theory surrounding the astonishing Cambrian Explosion.

Coupled with this research, I asked Dr Raub what the chances are of a repeat set of conditions that would lead to a similar, if not an exact repeat, in accelerated evolution for the modern day. The response was cryptic, yet intriguing.

“Overall, more continents today are drifting toward the equator than toward the poles.  So it is likely that in another 50 million years, global biodiversity will be higher than it is today, all else equal. However, the modern world is irreversibly different than Cambrian Earth. The stunning explosion of Cambrian animal life surely had a lot to do with expansion into previously empty ecospace. Readers might ask themselves, on Earth today, is every niche occupied?”

A gap in a niche would certainly provide scope for this phenomenon repeating itself. Today, anthropogenic impact to the World makes headline news and has led campaign groups to protest against our selfish actions and consider the Earth. We are forced to acknowledge our stewardship role and have changed our ways in order to cater for the needs of other species. However, rates of extinction are ever-growing. Earth is a dynamic system and is constantly evolving. This provokes the idea that there will be always be unoccupied niches in the system, even if they are not apparent.

The reconciliation of these contrasting theorems for the Cambrian Explosion, neatly ends the hot debate with victory on both sides. Wouldn’t it be satisfying if all arguments could be amended in this way?



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