This object is thankfully not coming anywhere close to Earth, but an impact of an object this size with Earth would still not sterilize the biosphere, or even evaporate the oceans.
It'd certainly sterilize the vertebrate part of the biosphere: a significant part of its chemical composition (per the paper) should theoretically be CO and HCN. "Hypervolatiles" is the term the paper uses—primordial evils that can only exist in the coldest outer reaches of the Oort cloud, far away from the star that evaporates them.
I don't know the exact numbers, but for water ice the "frost line" is at about 3 au (between Mars and Jupiter)[0]—the line inside which icy comets and ice moons, like Europa, can't form. Presumably there's analogous zones for the increasingly volatile cryogenic ices, going out into the most distant regions—a solid carbon dioxide line, a carbon monoxide line, a cyanide line... The surface of Pluto, for example, is mostly solid nitrogen, with parts of solid methane and solid carbon monoxide [1].
I don't think anything beyond the elemental composition of the impactor would matter much since the impact would heat it to a temperature at which it would be in chemical thermodynamic equilibrium, regardless of what its initial molecular composition was.
The KT impactor has been estimated to have been about 10 km in diameter and moving at 20 km/s.
A long-period comet, like an Oort cloud object, might impact at 50 km/s, instead of the 10-20 km/s of a near-Earth asteroid.
The physics might say that the energy might not be enough to literally vaporize the oceans or "sterilize" the biosphere, but the global ecosystem is fragile. This thing dropping on the planet would absolutely cause a mass extinction.
Oh, I didn't say the results wouldn't be utterly catastrophic. It's more a comment on just how surprisingly large an impact would be needed for sterilization.
I think you should read the text a bit more closely. A 700km impactor would be required to completely boil the oceans into vapor, but the article mentions that a much more insanely huge impactor of between 2000 and 2,700km would be needed to genuinely sterilize the earth because it entirely melts the crust.
However, (and here I speak from reading many other sources on this subject), even something the size of that latter object (basically something the size of a planet like Pluto) might not be enough.
Other studies have indicated that it might be exceptionally hard for heat to transfer enough through the vast mass of the earth's upper mantle and crust to actually melt it uniformly even if hit by something like the object that may have formed the moon.
This impactor was also supposed to be roughly 2,500km across and some of the theoretical concepts around it argue that even in that absolutely cataclysmic scenario, at least a part of the crust remains intact and relatively cool below a depth of several hundred meters.
If such a thing were to be true in the context of modern earth, which teems with life in every single possible remotely habitable nook and cranny and crevasse, then even a colossal impact by a 2,700km planet-type object wouldn't sterilize the Earth of life.
If only part of the crust remained intact as described above, then after hundreds of thousands or a few million years, as the earth's partially molten surface cools, and an atmosphere reforms, water that also reforms from vapor would rain down to the surface again in a vast global storm like something out of the bible. As this happens and the oceans refill, the tiny organisms concealed during all that time inside the deep cracks hundreds of meters below the surface of that surviving part of our world's crust would then recolonize the surface eventually and cause life to flourish again.
The key things in this scenario are that for one, at least one small part of the crust remains intact and cool, at least below a certain depth, and secondly, that water vapor eventually re-condenses into rain.
One might think that water would be vaporized right into separation of its hydrogen and oxygen atoms by the heat of such impacts, but mostly no. For that to happen the water on Earth would need to be subjected to at least something like 3,000 degrees Celsius of sustained heat, and even a planet-sized impact wouldn't generate such temperatures over most of the world.
Fair enough but why not just say the much larger other size they specifically mentioned. It's not about it being bigger than 700km but about it being enormously bigger (bearing in mind how volume expands cubed) to a specific size they also name.
Anyhow, sparked me into really thinking about all this again and the link you added was wonderful for that.
I don't think anymore absolutely 100% sterilization of all life on Earth is possible, we always end up talking about 99.999999% or similar. With exception of maybe super/hypernova of our Sun which ain't possible, or black hole passing directly through/very close to Earth, tearing apart every single atom making up this planet including all of us on quark level.
Even then there's a chance a few tardigrades hibernate on some material that shoots up and then comes back a few years later once the earth has cooled a bit.
I propose we do this intentionally - put a few tardigrades and some other extremophiles in a rad-shielded container inside a fully-passive reentry vehicle and throw it up into a graveyard orbit for a couple million years. Cheap insurance for life on earth!
Tardigrades were placed in the "extremophile" class with good reason. If anything could survive a truly catastrophic impact event, I'd say the smart money goes on the lowly "water bear" to win. :)
Tardigrades are not "extremophiles", which refers to organisms that live (grow, reproduce) in "extreme" environments ("phile" = "like, love"). Tardigrades can temporarily survive some rather extreme conditions, but they generally require fairly ordinary environments to actually live. (As suggested by common names like "water bear" and "moss piglet".)
Imply that the kinetic energy released upon the impact of such an object, show a group sheltering at the ISS (orbit at an altitude of between 370–460 km (200–250 nmi)) or the Tiangong (orbit between 340 and 450 km (210 and 280 mi) ) would not be likely to survive the impact from ejecta thrown into their orbital altitude...
We are looking at eject reaching orbits of 2500 Km to 3000 Km above Earth. Heat and corresponding vaporization effects excluded for simplification purposes.
Now we wait for an event to validate my calculations....
