Impact

New from the "Well, I Guess That's A Silver Lining?" department, we have: a massive meteorite collision 3.26 billion years ago that may have jump-started the evolution of life on Earth.

And I do mean massive.  This particular meteorite, given the unprepossessing name "S2," is estimated to have been a hundred times heavier than the Chicxulub Impactor that wrote finis on the Age of the Dinosaurs around 66 million years ago.  The S2 impact in effect took a chunk of rock four times the size of Mount Everest and slung it toward Earth at the muzzle velocity of a bullet fired from a gun.

The evidence for this impact was found in one of the oldest exposed rock formations on Earth -- the Barberton Greenstone, on the eastern edge of the Kaapvaal Craton in northeastern South Africa.  Geologists found tiny spherules -- microscopic glassy beads that result from molten rock being flung upward and aerosolized.  The impact not only blasted and melted millions of tons of rock, it generated so much heat that it boiled off the upper layer of the ocean, and the liquid water left behind was turned into the mother of all tsunamis.

"Picture yourself standing off the coast of Cape Cod, in a shelf of shallow water," said Nadja Drabon of Harvard University, who led the study.  "It’s a low-energy environment, without strong currents.  Then all of a sudden, you have a giant tsunami, sweeping by and ripping up the seafloor."

[Image is in the Public Domain courtesy of artist Donald Davis]

But this was a very different Earth from the one we currently live on; it's unlikely there was any multicellular life yet, and possibly not even any eukaryotic organisms.

"No complex life had formed yet, and only single-celled life was present in the form of bacteria and archaea," Drabon said.  "The oceans likely contained some life, but not as much as today in part due to a lack of nutrients.  Some people even describe the Archean oceans as ‘biological deserts.’  The Archean Earth was a water world with few islands sticking out.  It would have been a curious sight, as the oceans were probably green in color from iron-rich deep waters...  Before the impact, there was some, but not much, life in the oceans due to the lack of nutrients and electron donors such as iron in the shallow water.  The impact released essential nutrients, such as phosphorus, on a global scale.  A student aptly called this impact a ‘fertilizer bomb.’  Overall, this is very good news for the evolution of early life on Earth, as impacts would have been much more frequent during the early stages of life’s evolution than they are today."

Well, "very good news" for the survivors, I guess, but the life forms caught in the boiling-hot tsunami or the ones that got bombarded by a rain of molten rock spherules might have disagreed.

But being bacteria, their sky-high reproductive rate certainly allowed them to rebound rapidly, especially given that the impact had basically blenderized the oceans, churning up vast amounts of iron- and phosphorus-rich sediments.  This triggered a planet-wide bacterial bloom, and it's likely that once the dust settled, the Archean oceans were once again thriving.  Even though the first eukaryotes were still over a billion years in the future, the stage had been set for the slow progression that would ultimately lead to the tremendous diversification the ended the Precambrian Era.

So even a collision from a piece of rock four times bigger than Everest didn't wipe out all life, which -- as I said earlier -- is, I suppose, the silver lining to all this.  As Ian Malcolm so famously put it, "Life, uh, finds a way."

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