About 540 million years ago, something happened in the world's oceans. From being a desolate place with simple organisms, they suddenly exploded into life and a multitude of different species emerged.
But what caused the so-called Cambrian explosion is something researchers disagree on. It is clear that the temperature rose, the continents broke apart, and the sea level rose. On the shallow continental shelves, there was heat, sun, and algae, and additions of iron and phosphorus from the landmasses.
I see it as a new buffet opening up during the Cambrian period with masses of nutrients and food, says geobiologist Emma Hammarlund, associate professor at Lund University.
"Most turbulent environment"
But the ancient animals that wanted to take part in this feast faced problems. Hammarlund and her colleagues have calculated through computer models that there were large differences during the day. During the day, algae produced masses of oxygen. But at night, photosynthesis stopped, while the algae continued to consume oxygen and thereby depleted the areas of the substance.
You also have storms and chaotic, chemical conditions. It's the most turbulent environment on Earth. But it's also where there's the most nutrients.
She believes that this contributed to the animals having to evolve. It's about cells and tissues reading oxygen levels and adapting. Over a few million years, this leads to the emergence of many new species.
One can say that all animal groups we see today emerged during the Cambrian explosion or shortly thereafter. Above all, the ones we call invertebrates – which do not have a backbone but have hard parts – such as snails, mollusks, and arthropods.
Took giant leaps
For today's animals in the oceans, it's no problem living under the conditions that then arose. But evolutionarily, the ancient animals must have taken giant leaps.
Previously, researchers have believed that development was driven by the fact that oxygen levels on the planet increased during this period – that the conditions simply became more favorable. But Hammarlund believes rather that it was the opposite – that it was the difficulties, in combination with the opportunities that arose – that forced development.
This study hopefully shifts the focus from looking up in the air, and what has happened there over millions of years, to looking down at sunny, warm, shallow sea floors and seeing what happens there during day and night.
The researchers have used a biogeochemical model to calculate how oxygen levels were affected during the day in shallow waters during the Cambrian period, 539–485 million years ago.
It was a warm time on the planet, with ice-free poles, and large shallow seas emerged when the continents drifted apart and the sea level rose.
During the Cambrian period, a multitude of new animal species emerged in the oceans, something called the Cambrian explosion.
At that time, there was almost no life on land, possibly with the exception of algae, fungi, and lichens.
The study is published in Nature Communications.
