The Earth’s surface experienced the largest crustal erosion event in Earth’s history some 700 million years ago, paving the way for animal life to develop, according to a major new study involving the University of Southampton.
A team of scientists present compelling new evidence for scouring of three to five kilometres across all the continents during the Neoproterozoic Era (one billion to 550 million years ago) which would have seen the Earth’s crust washed into the oceans in unprecedented volumes. The research is published in the journal PNAS.
The discovery provides the strongest explanation yet for the origin and extent of the ‘Great Unconformity’ – a profound gap in the Earth’s rock record – exposed most dramatically in the Grand Canyon in the United States. Here, sedimentary rocks from the Cambrian era, which began 550 million years ago, were deposited directly on top of rocks from the Mesoproterozoic era, which ended one billion years ago.
The erosion happened when most of the Earth’s surface was covered in ice during a severe glaciation, dubbed ‘snowball Earth’, that lasted over 50 million years.
Dr Thomas Gernon, Associate Professor in Earth Science at the University of Southampton, and co-author on the study, said: “The findings help explain a fundamental enigma of Earth’s history, whilst also having profound implications for mineral exploration in ancient terrains worldwide.
“A massive proportion of ancient rocks were simply scraped off the surface of the Earth in an abrupt event like no other in Earth’s history.”
Whilst preserved rocks from this era are sparse, the scientists were able to study a database of 30 thousand zircon crystals formed in magmas – essentially ‘time capsules’ that preserve vital information on the chemical conditions that prevailed on Earth when they crystallised. These tiny inclusions were critical to unlocking the evidence for massive recycling of sediment into the interior of the Earth in a process known as subduction.
The team also made the remarkable observation that Earth’s largest asteroid impact craters were largely missing in rocks older than 700 million years, supporting the idea of deep global erosion. This process reconfigured the Earth’s surface and paved the way for the origin of animal life during the Cambrian era, known as the ‘Cambrian Explosion’, by changing the shape and chemical composition of the oceans, giving animals the environments and nutrients, they needed to evolve.
Dr. Brenhin Keller, a postdoctoral fellow at the Berkeley Geochronology Center, who led the study, said: “Our study unifies a diverse set of geological observations and may prompt a fundamental reassessment of the relationship between erosion, sedimentation and sea level, on billion-year timescales.”