There are many theories on how this massive event of diversification started 550 million years ago. It could have been the rising sea levels and temperature or a volcanic explosion from a continents super mountain, but I think the theory that sticks out to me the most is the theory that a slight spike in atmospheric and oceanic oxygen tipped the scales into a new era of dominating aerobic organisms.
The Cambrian explosion started from a mass extinction during the previous period, leaving a drop in biodiversity. During the Neoproterzoic era, there were two geological events called the Gaskiers glaciation and the Great Uncomformity (I like this name it sounds so silly) that prompted huge amounts of nutrients/ minerals to flow into the ocean from neighboring landmasses. Both commonly referred to the as the Snowball Earth events, which basically consisted of glacial ice melting and massive landslides/ erosion, allowed for an organism that utilized photosynthesis to quickly multiply. These organisms are known as cyanobacteria! Though they have been around since almost the start of life on earth (around 2.7 billion years ago), this event led to a huge bloom of cyanobacteria which in turn produced even more oxygen than before due to their boost in population. The oxygen byproduct gradually drifted into the atmosphere, turning a nitrogen riddled atmosphere into a richly oxidized one. Their increase in individuals gave way to another massive event called the Great Oxidation, which changed the Earth’s chemistry composition and is what led to a massive branching in evolutionary history.
The Great Oxidation Event which is fantastic for us, basically led to a mass extinction of anaerobic organisms. This event and prior extinction is what triggered the Cambrian explosion (explosion of 6 million years- a super long time for us but a blip in history for our planet).
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