Academic journal

Ancient asteroids frequently hit Earth, delaying the rise of life – study

Asteroid impacts remain one of the most dangerous natural disasters possible, but catastrophic collisions have been few in living memory. However, this was certainly not the case for Earth’s early years, when the young planet was furiously bombarded by massive ancient asteroids – 10 times more often than previously believed – and possibly delayed the planet’s ability to support life, a new study has found.

The impacts recorded in the study took place during the Archean Eon, a period between 2.5 billion and 4 billion years ago. At that time, the environment on the planet was very different – and being bombarded by asteroids undoubtedly changed the landscape even more.

By analyzing the remains of asteroids, scientists created a model of the effects of these collisions. According to their findings, published in the academic journal Geosciences of nature, major asteroid impacts have occurred about once every 15 million years, 10 times more frequently than current models suggest.

They weren’t small asteroids either, with some of them measuring around 10 kilometers.

For comparison, NASA has labeled any asteroid 140 meters or more approaching the planet as a potentially dangerous asteroid (PHA), due to its potential to cause catastrophic damage to Earth.

Asteroid impact: how to prevent one? (credit: PIXABAY)

When these massive asteroids hit the planet, it resulted in the creation of impact spherules. These form when asteroid impacts melt and vaporize parts of the planet’s crust, forcing them to form a giant plume above the surface before the molten rock condenses and solidifies. It would then fall back to the planet as particles the size of sand grains, settling in the crust. The more layers of impact spherules there are, the more impacts there would have been.

These are very difficult to find, but the discoveries made in recent years have increased scientific understanding of the number of impact events during this period.

But the influence of these asteroid impacts can go far beyond the simple destruction of the landscape. In fact, they may have changed the very chemistry of the atmosphere.

THE ARCHAEN The Eon was the time when life began to form on Earth, along with the slow build-up of oxygen in the atmosphere.

Oxygen itself was not present in the atmosphere in significant amounts until the early Proterozoic Era 2.5-541 million years ago, after anaerobic algae released it for photosynthesis.

But it is now believed that it is possible that the oxygen had accumulated earlier – without these asteroids.

    An asteroid is heading towards the planet in this artistic interpretation.  (credit: PIXABAY) An asteroid is heading towards the planet in this artistic interpretation. (credit: PIXABAY)

“The cumulative mass of the impactor delivered to early Earth was a significant ‘sink’ of oxygen, suggesting that early bombardment may have delayed the oxidation of the Earth’s atmosphere,” said lead author, the Dr Simone Marchi of the Southwest Research Institute at Stanford University in a statement.

This is because asteroid impacts produce reactive gases, which can smother low levels of oxygen in the atmosphere.

But as time passed and bombardments were less frequent, oxygen levels in the atmosphere began to rise, in what was called the Great Oxidation Event (GOE).

“The impact vapors caused episodic low oxygen levels for long periods leading up to the GOE,” Marchi said. “Over time, collisions gradually become less frequent and too small to be able to significantly alter post-GOE oxygen levels. Earth was about to become the current planet.

The destructive nature of even the smallest asteroids is well known to experts, with space agencies around the world monitoring potential catastrophic impacts and looking for potential ways to stop them.

One method of possibly stopping the impact of an asteroid is to use deflection, which would mean throwing something to slightly alter the path of an asteroid. The most important of these efforts is the DART (Double Asteroid Redirection Test) mission, which is due to launch in November, the result of the efforts of NASA and the Applied Physics Laboratory.

Simply put, it means hitting an asteroid with a rocket with sufficient speed to change its direction by a fraction of a percent.

However, this method has its flaws, most notably the timing. The spacecraft used in the DART mission took a lot of time and resources to develop and get started. In the event of an asteroid impact that seems so sudden, that kind of weather could be a luxury the planet cannot afford.

ANOTHER METHOD proposed in July 2021 by the Airbus company suggested an alternative: reuse television satellites by essentially hijacking them and using them as an ad hoc means to deflect the asteroid.

The science behind this method seems solid, although it also has its flaws, such as being able to deflect the asteroid when it is far enough from the planet. This could hypothetically mean more than six months.

Other methods focus on the disruption, that is, the destruction of the asteroid. A recently proposed method suggested using a nuclear explosion when the asteroid is far enough away, with the majority of the fragments passing, although it would still take time.
Another proposed method uses kinetic penetrators to detonate the asteroid’s core, and this could be accomplished in a much shorter time frame.

The fragments would then be dispersed into a cloud of fragments and, if not completely deflected, would then move into Earth’s atmosphere at speeds of around Mach 60.

But that’s where Earth’s atmosphere comes in, because entering the atmosphere at such a high speed puts it through high levels of heat and pressure. These constraints would in turn cause the fragments to explode further, creating a sort of sonic boom.

This may sound terrifying to some, because, as the scientists involved in the study noted, it would appear similar to the explosion of a thermonuclear bomb. But it would only be a big and harmless “sound and light” show, so there is no risk of nuclear radiation. The dust could still be present, but it would not be so catastrophic as to cause a global climate catastrophe scenario.

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