Astonishing Moments Asteroids Changed the Course of History

In the 1998 blockbuster Armageddon, all life on Earth was threatened by an asteroid the “size of Texas.” In fact, anything over half a mile in diameter would be enough to trigger a global catastrophe. Fortunately, such impact events are exceptionally rare. But when they have happened, the effects have been profound, shaping the history of the planet and everything on it.

In this article, we’re focusing on the times asteroids have dramatically changed the course of life on Earth. And we’re starting with some terminology. So read on, ‘cause you won’t want to miss a thing.

Asteroids are themselves the result of the biggest event in known history. Sometimes called minor planets, they are the debris left over from the formation of our solar system about 4.6 billion years ago. NASA defines an asteroid as “a relatively small, inactive, rocky body orbiting the sun.” And, by “relatively small,” the space agency means anything from a few metres to hundreds of miles in diameter.

Most known asteroids, of which there are approximately 1.3 million, rotate around the sun within the “main” asteroid belt between Mars and Jupiter. By contrast, Trojan asteroids share an orbit with a larger planet, while Near-Earth Asteroids are those with orbits that pass close to that of Earth. Finally, asteroids that actually cross Earth’s orbital path are known as Earth-crossers.

Impact events occur when asteroids collide with planets or moons, leaving behind craters and other measurable effects. These events have significantly shaped the evolution of the Solar System, influencing planetary surfaces and atmospheres. On Earth, several impact events have left an indelible mark on the planet’s history, altering its geology and the very story of life itself.

Of all the most famous asteroid collisions known to date, there’s one that stands out. In academic circles, it’s referred to as the Chicxulub Event. But most know it as the one that killed the dinosaurs. It happened approximately 66 million years ago, when a colossal asteroid, over six miles in diameter, struck what is now Mexico’s Yucatán Peninsula while travelling at more than 58 times the speed of sound. The energy released by the impact has been estimated as being as much as 4.5 billion times that of the Hiroshima atomic bomb. And the effects were devastating, starting with 1,000-foot tsunamis, powerful earthquakes and devastatingly high winds at and around the impact site.

Then came a sort of nuclear winter; the release of soot, debris, and greenhouse gases causing a global climate catastrophe. And it was this global warming that’s widely considered the primary cause for the mass extinction that took place, wiping out approximately 75% of all species on Earth, among them all non-avian dinosaurs. This, in turn, is thought to have paved the way for mammals to become the planet’s dominant life forms, eventually leading to the evolution of humans.

Asteroids need not impact the Earth’s surface to cause mass destruction. On 30 June 1908, an asteroid estimated at about 130 feet wide exploded at an altitude of about six miles above the remote Tunguska River in Siberia. The blast, Earth’s largest impact event in recorded history, was so powerful, it flattened an area of forest across an area larger than London.

More recently, on 15 February 2013, a meteor about 66 feet in diameter exploded around 14 miles above the Russian region of Chelyabinsk Oblast. The event released energy equivalent to 440 kilotons of TNT, creating a shockwave that injured over 1,500 people and caused extensive property damage.

Scientists continue to research asteroid impact events, hypothesising that we have yet to discover other instances where they altered the course of history. Some of the most prevalent hypotheses include:

The Hadean Bombardment Hypothesis

It’s widely thought that, during the Hadean eon, approximately 4 to 4.5 billion years ago, Earth experienced intense asteroid bombardments that profoundly altered its surface. These collisions reprocessed the planet’s upper layers, burying and melting them repeatedly. Giant impacts during this time likely vaporised oceans and created steamy atmospheres. Such events would almost certainly have played a critical role in shaping early Earth’s geology and may have influenced the emergence of life. For instance, any life forms during this period would have needed to withstand extreme conditions, potentially thriving in underground or underwater niches.

The Giant-Impact Hypothesis

Among the significant impacts during the Hadean eon, one stands out: the Giant-Impact Hypothesis. This theory suggests that a Mars-sized dwarf planet collided with the early Earth, ejecting a vast amount of debris into space. This debris eventually coalesced to form the Moon. If correct, this monumental event not only gave Earth its natural satellite but also significantly influenced its rotational dynamics and geological evolution.

The Great Ordovician Biodiversification Event Hypothesis

Around 466 million years ago, it’s thought that two vast asteroids collided somewhere beyond Mars. The resulting dust cloud was thought to be dense enough to block sunlight from Earth triggering a series of ice ages. But it was what happened afterwards that captivated scientists. Because, in the wake of these ice ages, the Earth experienced a biodiversity explosion in its oceans.

In 2016, NASA established the Planetary Defense Coordination Office. Not only does this organisation track near-Earth objects, but it develops strategies to mitigate potential threats. One such strategy is asteroid deflection. The Double Asteroid Redirection Test, or DART, mission launched in 2021, successfully altering the orbit of the asteroid Dimorphos by crashing into it. This mission demonstrated our ability to potentially divert a hazardous asteroid, providing a blueprint for future planetary defence initiatives.

As we’ve seen, asteroid impacts have profoundly shaped Earth’s history, probably influencing the formation of the Earth-Moon system, driving evolutionary changes, and causing mass extinctions.

From the cataclysmic Chicxulub event to the Tunguska explosion, asteroids have sculpted our world and changed the course of evolutionary history. These cosmic collisions may have even contributed to the origin of water on Earth, and delivered the building blocks for life itself.