One of the most dramatic and seemingly inexplicable events in the history of Earth’s biosphere occurred roughly 540 million years ago when multi-cellular life exploded all over the planet. This large-scale diversification of life is known as the ‘Cambrian explosion’ and lead to the variety of organisms we see on Earth today. Scientists have often attributed the Cambrian explosion to significant geologic or climatic changes on our planet, but new NASA-sponsored research may have a better explanation.

Rather than catastrophic disruptions in Earth’s climate, a new study indicates that the Cambrian explosion may have been caused by more gradual environmental changes that began hundreds of millions of years earlier. By gathering and compiling numerous published measurements of the carbon and oxygen isotopic composition of limestones that formed during this period of time, researchers were able to look at the bigger picture surrounding life’s diversification. This lead them to formulate different scenarios for what led to complex life on Earth. Rather than a world subjected to life-altering catastrophes, they saw a world that first greened up with primitive plants. The researchers believe that an explosion of photosynthesizing life began on Earth some 850 million years ago, ultimately causing the formation of large amounts of carbon-bearing soils and facilitating the rise in atmospheric oxygen that set the stage for the expansion of multicellular life in the Cambrian explosion.

A paper concerning the research, under lead author L. Paul Knauth of Arizona State University, was recently published in the journal Nature.