It was the end of the world as they knew it
And they did not feel fine. In fact, 66 million years ago was a very bad day to be alive.
66 million years ago the dinosaurs went extinct. For a long time it was unclear exactly why all dinosaurs suddenly disappeared. It was not until quite recently that geologists found out that the geological layer corresponding to the dinosaur extinction event contained surprisingly high levels of the element iridium. Iridium is quite rare on Earth. But it is a common element in many types of asteroids. Scientific discussion continued until a 66 million year old impact crater was found in Chicxulub, just outside the Yucatan peninsula.
The dinosaurs had no telescopes and no astronomers. 66 million years ago no one on Earth noted the asteroid that was going to end the world until about 60 hours before impact. Then it looked like a very faint star. For the next 60 hours that faint star would rush towards Earth with a relative velocity of 20 km/s. Something was about to happen.
Boom
The asteroid that hit Earth was about 10 km in diameter and had a mass of something between 1012 and 1013 tons. When it entered the atmosphere it hit air molecules resulting in friction and a lot of heat. Enough energy was created to turn the molecules in the area into plasma. The heat also made the air expand with a speed greater than sound. The resulting sonic boom was loud enough to be heard everywhere on Earth.
The asteroid hit an area of shallow ocean, a few hundred meters deep, just north of the Yucatan peninsula, outside today's Mexico. The immense heat from the atmosphere passage had evaporated all water from the ocean and the asteroid impacted the dry ocean bottom. The rock in this area was 3 km of limestone and anhydrates on top while the underlying rock was harder granites.
When the asteroid hit, the rock was immediately liquefied and the impact with the dry ground must have looked something like when one throws a pebble into water. Tremendous volumes of liquefied rock were thrown up in the air. Substantial amounts reached orbital velocity and disappeared into space. For Earth as a whole the asteroid impact was probably a net loss of mass.
Naturally, the impact also generated a tsunami in the surrounding ocean, the parts that had not evaporated. Modeling has revealed that this tsunami affected the coastlines of the entire Atlantic and Pacific Oceans and devastated the northern shoreline of the Mexican Gulf, today's southern United States, with waves in excess of 50 meters.
At the time, hardly anyone should have cared for the tsunami since tsunamis are quite slow and a lot of other things would have happened before they cared to arrive. Direct effects of the impact was not unlike a very powerful nuclear weapons detonation. Intense heat radiation and a shockwave destroyed everything in a radius of up to 1000 km.
But the greatest effect was from the molten rock that was ejected from the impact site. Some of this ejecta was lost to space but most of it fell down to earth again. The ejecta was very hot when it was blasted away from the impact site. High up in the atmosphere it cooled down and solidified into a form of glass shards known as tektites. When these tektites fell down towards Earth again atmospheric friction heated them up once more. Scientists estimate that the asteroid hit Earth at about 45 degrees angle from the north-east (probably, there seems to still be considerable scientific debate about the direction of impact), meaning the debris from the impact was mostly thrown in a south-westerly direction.
Most of the tektites probably fell in areas close to the impact site. But significant portions of the ejecta went ballistic, reaching altitudes at the very edge of space, and spread over the entirety of Earth. Every part of Earth was consequently battered by glass stones. Most of the tektites were small, no more than beads. But some were bigger, up to several tens of kilograms, presenting a real danger to everything on the surface.
Not that it mattered very much on the whole. When the tektites were falling down through the atmosphere they were not the only thing that was heating up. The friction heat they generated also heated the atmosphere. The atmosphere radiated its extra heat downwards towards the surface of Earth which experienced a heat pulse for several hours. The exact magnitude of this heat pulse varied across the globe but it was enough to set the entire world on fire. Something that is very visible in the geological record where the layer corresponding to Chicxulub event is marked by a thin black layer of pure soot.
Quiet
In less than a day most of life on Earth had ceased to exist. The blast and the heat wave from the impact instantly killed everything close to the impact site. Falling tektites must have killed scores more. But the greatest killer of all was undoubtedly the heat and the fires that the heat ignited.
Basically everything on the surface of Earth died that day. It is probably fair to say that it was the mother of all catastrophes. However, significant reservoirs of life still existed. Foremost of these was, of course, the oceans. Neither the tektites, nor the heat pulse had much effect on ocean dwelling life. Even on land there was plenty of life surviving, burrowed in the ground or hiding in caves or ponds.
Cold
Unfortunately for life this was only the first part of the catastrophe. When the asteroid hit Earth it did not only throw molten rock into the atmosphere. It also threw up enormous amounts of dust and other particles. The immense fires that engulfed the world also created soot and ash which was also added to the atmosphere.
Both the asteroid impact and the gigantic fire storms had the ability to lift particles and soot above the tropopause and into the stratosphere, where they lingered for years. It was not only dust and soot that entered the atmosphere. The asteroid had hit an area with lots of anhydrates in the ground, basically a form of gypsum. And gypsum contains sulfur. Lots of sulfur was ejected into the atmosphere where it formed tiny particles of sulfur dioxide, particles that are very efficient at blocking sunlight.
All this had an immediate and very powerful effect on the climate. Up to 99% of all sunlight was blocked from reaching the Earth's surface, creating a dusk-like environment where almost all photosynthesis halted. This almost total blocking of the sun led to an "impact winter" in which air temperatures may have fallen up to 26 degrees, turning previously tropical areas arctic.
This impact winter was even more deadly than the asteroid impact and its corresponding fires. Especially the oceans, largely unharmed from the impact and the impact fires, were hard hit by the lack of sunshine. All life in the oceans are dependent on phytoplanktons and their ability to turn sunlight into energy. Without sunlight there were no phytoplankton and this rippled through the marine ecosystems with devastating effects.
The oceans had another, more long-term problem. The sulfur dioxide that blocked sunlight eventually fell down, but then as sulfuric acid. The amounts of sulfuric acid were large enough to affect the acidity of the oceans. The oceans did not turn into sizzling acid seas but a slight lowering of pH was enough to make life impossible for a number of shell-building creatures, adding a few more species to the already long list of extinction.
Bad luck galore
Asteroids hit Earth with some regularity. But large ones, like the one that hit Chicxulub, are very rare. In fact, we know of no asteroid hit on a dinosaur extinction level, after Chicxulub asteroid hit.
On the other hand, most of Earth consists of oceans, and oceans do not leave much trace of asteroid impacts. In fact, it could be said that the Chicxulub asteroid hit in the worst spot imaginable.
Had the asteroid hit in the deep ocean, the mass of the water would have taken the brunt of the impact energy. Most of the water at the impact site would have evaporated, but probably not all, and the asteroid's energy would have been diminished enough to not be able to throw either tektite creating liquid rock or impact winter inducing dust into the atmosphere. There would have been a huge tsunami, of course, but the effects would have been transient in comparison to what did happen.
The Chicxulub asteroid impacting shallow ocean might have been the worst possible outcome. The water was too insignificant to weaken the impact energy in any meaningful way. But the water did transmit significant amounts of water vapor to the atmosphere. Combined with the sulfur from the bedrock, that the asteroid also vaporized and threw up in the atmosphere, this created the sulfur dioxide that was a major component of the impact winter.
Nice catastrophe, but what about humanity?
The Chicxulub asteroid did it for the dinosaurs. But dinosaurs are famously small-brained. Surely a larger-brained species, like humans, would fare much better in a similar situation.
Most asteroid management planning assumes asteroids on collision course with Earth will be handled in space. Either by deflecting or destroying them, and in that way saving Earth from any destruction at all.
When we are talking about asteroids of a dinosaur killing magnitude this is most probably wishful thinking. A 10 km asteroid simply can not be destroyed with any weaponry humanity can muster. Deflection is a possibility, but it will be very difficult to achieve in practice.
Space deflection is hard
For a large object, like the Chicxulub asteroid, to be successfully deflected, efforts must be made as early as possible. This is a higher bar than might be realized at first blush. Deflection will most likely be made using nuclear weapons. Humanity has plenty of experience in handling nuclear weapons. But not in space. In fact, humanity has very little experience of acting in space at all.
This might come as a surprise to people used to hearing about the latest accomplishments of SpaceX et al. But humanity's space faring (and all of SpaceX's) is usually limited to orbital space flights, a couple of hundred kilometers above Earth's surface. In fact, humanity has only left Earth's orbit with anything big enough to carry a nuclear weapon on the few occasions when Nasa traveled to the moon, more than fifty years ago.
Compared to reaching an asteroid, landing on the moon is a walk in the park. The main problem with asteroids is the distance. If we want to hit a Chicxulub type asteroid a month before it hits Earth (depending on the weaponry this might not be enough time for deflection) we would have to reach it when it is 50 million kilometers away from Earth. That is more than a hundred times further than the moon and about as far away as Mars (when it is closest).
Distance is generally not a problem in space. Except the fact that it takes time to traverse. Reaching a suitable rendez-vous point with a threatening asteroid will probably take years of space travel. Add to this the time for designing and constructing the necessary space vehicles and we are talking about total time scales of a decade or more.
Digging in is easy
The nasty surprise here is that even if we detect a catastrophic asteroid years or decades in advance we might not be able to stop it colliding with Earth. This is unfortunate to say the least, but it might not mean the end of humanity.
After all, we are mammals, and terrestrial mammals survived the Chicxulub disaster by hiding underground and eating seeds and other leftovers from before the catastrophe. Nothing stops us from repeating that success. Being humans, we have a head start. For several hundred years now humanity has built underground dwellings that are more than enough to protect us from the direct effects of a large asteroid impact. Sweden, and I suppose most other advanced nations, have bunker systems able to house the entire population in the case of nuclear war. Or asteroid impacts.
Surviving the direct effects of the impact is probably the easier part. An impact winter, in which agriculture may be impossible for several years, will be much more difficult. The world's stockpile of cereals would not even last half a year if production suddenly stopped. Other foodstuffs might last longer but it still seems a difficult task to keep humanity from starving in the case all agriculture ceases.
There is a silver lining though. The time from asteroid detection to impact might not be enough to organize a successful deflection, but it should be plenty to organize survival on the ground. Even a few years of forewarning is enough to build plenty of shelters and ramp up food production enough to get a surplus to store away in anticipation of an impact winter.
An asteroid impact the size of which killed the dinosaurs will inevitably be painful. But by planning ahead it should be possible to let most of humanity (I am thinking of at least 50% here) survive the disaster. Planning for asteroid disaster does not exclude planning for asteroid deflection. The two can be prepared for in parallel. Being versatile and adaptive are two of humans' many strengths. Strengths that will let us survive misfortunes that exterminated lesser species.
I have read a book again. This time it was The Last Days of the Dinosaurs by Riley Black. Everything in this article not explicitly sourced from somewhere else can be assumed to be from this book.
Good post Anders.
". . . we know of no asteroid hit on a dinosaur extinction level, after Chicxulub asteroid hit."
I understand that no other asteroid collision has caused a global mass extinction event.
On the other hand, an asteroid collision could well be a civilisation ending event, though even a large one would likely not be consequent enough to extinguish humanity.
The other global mass extinctions have been associated with changes in the earth's biota coupled with geologic changes triggering the mass extinction. I have seen suggestions that the global cooling over the past 70 million years has been a product of carbon removal from the atmosphere by flowering plants and grasses (and subsequent Carbon sequestration in sedimentary rocks) with the ice ages being triggered a million years ago when the world had cooled to the point when the milankovitch cycles began to have an effect. Not yet a global extinction event, though.
The Great Oxidation of the earth's sediments and atmosphere from about 2.5 to 2 Billion years ago by photosynthesising bacteria is the standout example of such a global mass extinction. More recently the greatest extinction event, at the end of the Permian era, was probably the culmination of changes to erosion and sediment deposition by driven by vascular plants covering the worlds land surface (with the extinction triggered by changes in plate tectonic activity, if I recall correctly).
This was your best post ever, with three caveats.
> Falling tektites must have killed scores more But the greatest killer of all was undoubtedly the heat and the fires that the heat ignited.
Missed a period.
> Had the asteroid hit in the deep ocean, the mass of the water would h have taken the brunt of the impact energy.
Extra h.
> It was the end of the world as they knew it And they did not feel fine. In fact, 66 million years ago was a very bad day to be alive.
Oh! Anders wrote a post about prehistory. I'll read half of this right now. Then maybe later read it to my broken-footed wife, who has nothing better to do than enjoy the thrumming of my voice as I read about low-impact science.
Your target audience has *no idea* how badly they want to read this post. Based on some digging around we'd done months ago, my wife and I assumed that we were already around the point of protecting people from asteroids, provided civilization didn't collapse. Now, obviously, we are not so sure.
But if this had been in my news feed, the headline would have read: "Scientists: The Dinosaurs are gone. We're Next" and I'd have immediately clicked on it, even knowing to expect the kind of uneducated, semiconvincing discussion that would likely follow. I'm not saying you should turn your articles into click bait, but somewhere in the first few paragraphs you could mention that "Fools Ignore The Skies At Their Peril."