According to a press report, a passing star caused the PETM.

"According to a new study published in The Astrophysical Journal
Letters, the relatively close passing of a star 56 million years ago
caused the Earth’s temperature to rise by eight degrees centigrade."

https://www.indy100.com/science-tech/earth-orbit-chance-encounter-star

The actual paper says that the star passed by 2.8 million years ago
(only a factor of 20 difference). What the paper says is that taking
account of perturbations caused by the flyby, the uncertainty in the
eccentricity of the earth's orbit at the time of the PETM is
considerably larger, which makes an orbital forcing more tenable as a
cause of the PETM.

https://iopscience.iop.org/article/10.3847/2041-8213/ad24fb

It doesn't strike me a plausible explanation for 200,000 year spike of
the PETM, on the reading that what the paper is reporting is a greater
uncertainty in the eccentricity, not a greater rate of change of the
eccentricity. A contribution to the generally elevated temperature of
the Palaeocene and Eocene may be more plausible.

--
alias Ernest Major

On Monday, February 19, 2024 at 8:23:13 AM UTC-5, Ernest Major wrote:
> According to a press report, a passing star caused the PETM.
>
> "According to a new study published in The Astrophysical Journal
> Letters, the relatively close passing of a star 56 million years ago
> caused the Earth’s temperature to rise by eight degrees centigrade."
>
> https://www.indy100.com/science-tech/earth-orbit-chance-encounter-star
>
> The actual paper says that the star passed by 2.8 million years ago
> (only a factor of 20 difference). What the paper says is that taking
> account of perturbations caused by the flyby, the uncertainty in the
> eccentricity of the earth's orbit at the time of the PETM is
> considerably larger, which makes an orbital forcing more tenable as a
> cause of the PETM.

It is true that due to it's chaotic nature, we cannot predict the evolution
of orbital parameters infinitely far into the past.

But observations (and such things as conservation of energy) do provide
some constraints.

In rocks laid down well before this event, (e.t. the Triassic) the temporal
signature of Milankovitch variations in orbital parameters is clear, and it is the
same signature we see in more recent records. It is not clear to me
that a passing object could induce major changes in orbital variations,
which later resume their previous behavior.

The long eccentricity cycles are controlled by interactions between
the Earth, Jupiter, and Saturn, will little impact from other bodies.
If either of these outer planets were seriously perturbed by
a passing object, the tempo of eccentricity changes should vary.

Eccentricity itself has little direct effect on the amount of sunlight reaching
the earth. It's major impact is in combination with the precession of
the equinoxes, and this is due to the gravitational pull of the moon
and sun. It will not be altered by perturbations in the orbits of
other planets, or by a plausibly higher eccentricity in the earth's orbit.

The linear effect of all orbital variations, to a very good approximation,
is to redistribute sunlight among latitudes and seasons, not to
contribute to a net warming or cooling of the planet. It takes
nonlinear feedbacks (e.g. ice albedo) to rectify the signal one
way or another.

William Hyde

On 19/02/2024 22:54, William Hyde wrote:
> On Monday, February 19, 2024 at 8:23:13 AM UTC-5, Ernest Major wrote:
>> According to a press report, a passing star caused the PETM.
>>
>> "According to a new study published in The Astrophysical Journal
>> Letters, the relatively close passing of a star 56 million years ago
>> caused the Earth’s temperature to rise by eight degrees centigrade."
>>
>> https://www.indy100.com/science-tech/earth-orbit-chance-encounter-star
>>
>> The actual paper says that the star passed by 2.8 million years ago
>> (only a factor of 20 difference). What the paper says is that taking
>> account of perturbations caused by the flyby, the uncertainty in the
>> eccentricity of the earth's orbit at the time of the PETM is
>> considerably larger, which makes an orbital forcing more tenable as a
>> cause of the PETM.
>
> It is true that due to it's chaotic nature, we cannot predict the evolution
> of orbital parameters infinitely far into the past.
>
> But observations (and such things as conservation of energy) do provide
> some constraints.
>
> In rocks laid down well before this event, (e.t. the Triassic) the temporal
> signature of Milankovitch variations in orbital parameters is clear, and it is the
> same signature we see in more recent records. It is not clear to me
> that a passing object could induce major changes in orbital variations,
> which later resume their previous behavior.
>
> The long eccentricity cycles are controlled by interactions between
> the Earth, Jupiter, and Saturn, will little impact from other bodies.
> If either of these outer planets were seriously perturbed by
> a passing object, the tempo of eccentricity changes should vary.
>
> Eccentricity itself has little direct effect on the amount of sunlight reaching
> the earth. It's major impact is in combination with the precession of
> the equinoxes, and this is due to the gravitational pull of the moon
> and sun. It will not be altered by perturbations in the orbits of
> other planets, or by a plausibly higher eccentricity in the earth's orbit.
>
> The linear effect of all orbital variations, to a very good approximation,
> is to redistribute sunlight among latitudes and seasons, not to
> contribute to a net warming or cooling of the planet. It takes
> nonlinear feedbacks (e.g. ice albedo) to rectify the signal one
> way or another.
>
> William Hyde
>

I've tracked down the press release

https://www.psi.edu/blog/passing-stars-altered-orbital-changes-in-earth-other-planets/

--
alias Ernest Major