Rare Cretaceous
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what are the limitations of this piece of evidence for the asteroid theory?
How could you criticise it?
"There is good geophysical evidence for the occurrence of an asteroid impact at the end of the Cretaceous.
A band of clay rich in the mineral iridium was deposited at the end of the Cretaceous and has been found at many places in the world. This mineral is rare on Earth but more common in meteorites.
It has been suggested that the impact would have triggered a nuclear winter scenario that would have caused the death of the dinosaurs as well as the pterosaurs, several families of birds and mammals and also marine animals such as the plesiosaurs and ammonites. "
Thanks
It makes assumptions that are not always easy to verify.
It uses observations that appear related but maybe are not as related as we think.
It makes conclusions that are not the only way of explaining what is observed.
Sorry, I cheated. These "limitations" are the same limitations that threaten every single theory.
The Big Bang makes assumptions that are not easy to verify.
The creating of a monotheist family of religion makes assumptions that are not easy to verify.
The theory of Relativity makes assumptions that are not easy to verify.
The idea that the Bailout will work is based on assumptions that are not easy to verify.
And so on.
The asteroid theory makes the assumption that the great extinction of the K-T inter-period was caused (or precipitated) by a single planet-wide event.
Since the chronology of the extinction seems to match the deposit of the iridium layer, we link the two.
The source of the iridium is deemed to be understood. It leads to the conclusion of a major impact by an asteroid (or many impacts at around the same time).
We calculate that such an impact would have effects on the Earth's atmosphere that could explain a major and rapid extinction.
At each step, there could be other explanations (albeit less probable); also the reasoning depends on how well we understand each step (does a "nuclear winter" really have that impact? It is not as if we ever observed one of that importance recently).
The doubts do not mean that the theory is useless (or "false" as the non-scientists would say). Only that we should keep an open mind for other possibilities. Of course, it does not mean that we should blindly accept any other possibility. Any other proposal must be at least as useful as the asteroid impact if it wants to be considered.
For example, a theory that dinosaurs disappeared because a bunch of hunters went out with big guns on a Sunday afternoon would not be very plausible.