Earth experienced two especially dramatic periods of mountain building, and both roughly coincided with increases in biological diversity. Researchers now argue that this alignment may reflect a profound link between towering landscapes and the rise of complex life.

Scientists have devoted enormous effort to understanding how life began, but some contend that its origin may not be the hardest part of the story. The first cells appeared relatively soon after Earth cooled enough for life to exist.

Complexity took far longer. Around three billion years passed before early organisms consisting of single cells began forming multicellular life more advanced than stromatolite colonies.

Dr Matthijs Smit of the University of British Columbia thinks the crucial explanation may be buried deep inside Earth. His proposal connects changes in the planet’s interior to taller mountains, erosion, ocean nutrients and biological expansion.

Higher mountains erode faster, releasing pulses of nutrients that eventually reach the oceans. Those nutrients can support more biomass and biodiversity, raising the possibility that mountain growth helped create conditions in which increasingly complex organisms could flourish.

“Changes that occurred deep in the Earth ultimately gave rise to much taller mountains over time, which may have made our planet habitable by providing the nutrients needed for life to form and flourish,” Smit said in a statement.

“Nutrients such as phosphorous are essential ingredients for life on our planet, but prior to three billion years ago, these elements were locked in the Earth’s crust and the oceans were quite nutrient-starved. All this changed when tall mountains started to develop.”

Modern mountain heights reveal little about ancient ranges because erosion can rapidly wear them away. Metamorphic rocks, however, preserve evidence of the conditions under which they formed, including the pressure created by the mountains that once stood above them.

Some mountains develop over mantle plumes, including Hawaii’s Mauna Kea. Most form where tectonic plates press against each other, as with the Himalayas, or where one plate moves over another, as with the Andes and Rocky Mountains.

Although plate tectonics have existed for a long time, exactly how long remains disputed. Smit and his colleagues contend that mountains produced during Earth’s early years were closer to what people today might regard as hills.

The ancient mountain belts stood on sections of crust that the authors estimate were around 30 km (18 miles) thick. That changed around 2.2 billion years ago, when mountain formation became far more substantial.

During that first major growth period, the tallest ranges rose to heights slightly below those of the modern Alps. In some places, the crust reached 60 kms (36 miles) thick.

Another transformation began around 700 million years ago, when mountains started attaining modern heights. Since then, several ranges comparable to the Himalayas have risen and eroded, while crust in suitable locations could exceed 80 km (48 miles) in thickness.

The researchers say both periods of increased crustal growth approximately align with major developments in Earth’s history. The first may have produced extensive land on a large scale, while the second pushed mountain ranges to enormous heights.

Each increase in crust thickness also approximately matches the timing of a great oxidation event. During these events, atmospheric and ocean chemistry changed significantly and helped the evolution of life forms that breathe oxygen.

Smit suspects the bursts of mountain growth were ultimately connected to the planet’s cooling mantle rather than atmospheric temperatures. As radioactivity within the core declined, the mantle slowly lost heat, became more rigid and could support thicker crust.

Even though heat loss was presumably relatively steady, its geological consequences appeared in bursts. Dr Ellen Kooijman of the Swedish Museum of Natural History said the timing of life’s development and diversification alongside the two mountain growth spurts was likely not coincidental.

“It’s exciting to think that mountain belts were once non-existent and that their development over the past three billion years may have driven the environmental and biological change that shaped our planet.” The open access study appears in Science Advances.