Want to know how Earth became Earth? A planetary takeover by ocean-dwelling algae 650 million years ago was the kick that transformed life on Earth and that algae burst is the very reason we are here! An algae? Really?

So some researchers believe that an algae is responsible for making Earth what it is today – a livable planet. That’s what geochemists are arguing about, on the basis of invisibly small traces of bio-molecules dug up from beneath the Australian desert. The molecules mark an explosion in the quantity of algae in the oceans. This in turn fueled a change in the food web that allowed the first microscopic animals to evolve, as per the claims of researchers who found this. The lead researcher of this phenomenon says that, “This is one the most profound ecological and evolutionary transitions in Earth’s history.”

The events took place a hundred million years before the so-called Cambrian Explosion, an eruption of complex life recorded in fossils around the world that puzzled Darwin and always hinted at some kind of biological prehistory. Scattered traces of those precursor multi-celled organisms have since been recognised, but the evolutionary driver that led to their rise has been much argued over. Cambridge University palaeontologist Nick Butterfield has said the period “was arguably the most revolutionary in Earth history”, and not just because of the rapid biological changes. There were violent swings in climate, too, that experts have long suspected are intertwined.

The context was a planet that previously had long had life-sustaining oceans and a benign climate. Yet, for over three billion years – since 3.8 billion years before present according to most estimates – all life was single-celled, mostly bacteria; little evolutionary innovation had happened. Algae, more complex than bacteria but still single-celled, had themselves been around for over a billion years (the “boring billion” some palaeontologists call it), but without making much of an ecological impact. With their DNA packed away safely inside a nucleus (so-called eukaryotes, like all animals and plants today), they had an evolutionary advantage over bacteria they seemed unable to exploit. That changed about 650 million years ago, according to the new study.

So the un-swayed conclusion by researchers of the new studies – the outburst of algae 650 million years ago “kicked off an escalating arms race” in which larger creatures, fuelled by their ocean-grazing, become prey to yet larger ones – until you end up with the complexity we see today.