Volcanic belch: A 10 m high fountain of lava in Hawaii. The ancient eruptions would have been on a different scale of magnitude and lasted for a million years or more.
Credit: Wikimedia
SYDNEY: The ancient Earth experienced bouts of cataclysmic volcanism that buried much of its surface in up to 15 kilometres of lava, says a new study.
The research from the Australian National University, in Canberra, reveals that these hellish episodes of volcanic activity each lasted for around one million years – but the last ended around three billion years ago, and the phenomenon is unlikely to occur again.
Study author Geoff Davies used computer models of the Earth's deep interior which revealed that for much of its early history, the planet's innards were a ticking time bomb.
Formation of the continents
The study, published this week in the journal Earth and Planetary Science Letters also provides vital new clues about how the Earth's first continents formed in several major bursts, two to three billion years ago.
Davies' model suggests that the early oceanic crust was pushed far below the surface, forming a barrier deep in the Earth's mantle.
This layer repeatedly prevented the molten rock from rising and cooling, allowing vast amounts of energy to bottle up, before it finally erupted with catastrophic effect.
"The deeper mantle is slowly heated by radioactivity. Eventually it gets hot enough to break through the barrier and rises in a rush [which]… erupts as lava flow," said Davies. "These lava flows could pile up to a thickness of 10 to 15 km over much of the Earth."
As well as providing the raw matter to form the continents, the epic explosions would have profoundly altered the chemistry of the oceans and atmosphere. This meant that only the toughest primitive bacteria would have survived long enough for the planet's tectonic plates to thicken and the phenomenon to come to an end.
Biggest eruptions ever
"The episodes happened about every hundred million years so the bacteria would have had plenty of time in between to recover," said Davies. "Eventually, as the Earth's interior slowly cooled, the tectonic plates became thick and heavy enough to break through the basalt barrier and prevent it from reforming, and no further episodes occurred."
"The volume of volcanic activity predicted by the models is enormous; several orders of magnitude greater than even the biggest eruptions we know from history." commented Sandra McLaren, a geoscientist at the University of Melbourne who was not involved in the study. "This is a highly significant new work for understanding our Earth's childhood and the layer-cake structure inside our planet."
McLaren noted that while this force was once powerful enough to form continents, "the slowing of the Earth's radioactive heat engine, as it has aged, means we're pretty safe from 'lava bomb Earth' in the future."
