The Cambrian explosion was the largest diversification of life in Earth’s history. Ocean life started as sparse and simple. Then, it diversified with a colossal amount of life forms.
For the first 3.5 billion years on Earth, only primitive life forms existed in the oceans. For instance, all organisms were without hard body parts at this time.
But the Cambrian explosion marked the first time in Earth’s timeline that we could observe fossils. For example, fossils include exoskeletons and shells from this period.
A shift in ocean chemistry started the Cambrian Explosion. In this remarkable evolutionary event, new life started in the ocean. Then, it eventually colonized the land.
The explosive burst of evolutionary life
Almost all animals today branched off from the first 40 million years of the Cambrian period. It went from primitive life to something resembling modern organisms today.
During the Cambrian period, there was an abundance of eukaryotic organisms that swam in the oceans. For example, trilobites, brachiopods and gastropods made their first appearance.
Climate was milder in the Cambrian period. When oceans spilled onto continents, shelled marine invertebrates are believed to have crawled on the land.
Algae likely existed but land plants didn’t. Earth resembled much like a desert so animals did not fully colonize the continent.
A shift in ocean chemistry sparked diversity
What sparked life to evolve during the Cambrian explosion that lasted over 20 million years? The main catalyst is believed to be a shift in ocean chemistry.
As calcium and magnesium levels in prehistoric oceans changed, so did the species that took residence. For example, organisms developed calcified body parts, flexible limbs and eyes.
One of the environmental triggers was an increase phytoplankton in the ocean. In our modern environment, phytoplankton are the largest producers of oxygen.
In prehistoric times, phytoplankton were responsible for increasing oxygen as well. As oxygen levels rose, it boosted the amount that could be used to drive metabolism.
Mass extinction ended most Cambrian life
The Cambrian period was a time of prosperity in the oceans. As revolutions of life sprung out, it was only followed by catastrophic extinction.
Earth has experienced 5 mass extinctions. More than 99% of species that existed are now extinct. No matter how far back you look, nature has found its way to reshuffle the deck. Cambrian life is no exception.
For example, ocean/atmosphere chemistry, climate change, volcanic activity and meteor/asteroid impacts have all caused fatal consequences for life on the planet.
As all life hinges on oxygen, scientists attribute the mass extinction from a sudden depletion of oxygen. It’s believed that oxygen temporary dropped from the upwelling of cooler deep ocean areas.