To me, this is a clear example of Fake Science and Confirmation Bias. A key quote is: “We posit that eccentricity pacing of phytoplankton evolution contributed to the strong 405,000-year cyclicity that is seen in global carbon cycle records.” Note, this is a ‘posit’, an assumption put forward as the basis for an argument. It’s not a ‘Theory’, not a ‘Hypothesis’, not even a ‘Conjecture’, the least of any scientific statement. Yet the 405,000 year and 100,000 year orbital eccentricity “cycles” are presented as fact.
There have apparently a number of studies of geologic records that find cycles hinting of repetitions at this length. The problem is that NO orbital periods have been found at 100,000 years or especially the precise 405,000 years. Existence of these is merely speculation. Look up “Milankovitch cycles” from any source and you will find that these orbital cycles have been studied for years, and none longer than about 40,000 years are known.
I attempted to follow the links and the links to the links in the articles, and no source 100,000 year and 405,000 year orbital cycles were there. There were discussions of 405,000 year geologic cycles, but no known orbital cycles.
Bro, huh?
I did just search on Milankovitch cycles and all the links showed 4 cycles:
https://en.wikipedia.org/wiki/Milankovitch_cycles
Orbital eccentricity
The major component of these variations occurs with a period of 413,000 years (eccentricity variation of ±0.012). Other components have 95,000-year and 125,000-year cycles (with a beat period of 400,000 years). They loosely combine into a 100,000-year cycle.
Axial tilt (obliquity)
The angle of the Earth’s axial tilt with respect to the orbital plane (the obliquity of the ecliptic) varies between 22.1° and 24.5°, over a cycle of about 41,000 years.
Axial precession
Axial precession is the trend in the direction of the Earth’s axis of rotation relative to the fixed stars, with a period of 25,771.5 years.
Apsidal precession
The orbital ellipse itself precesses in space, in an irregular fashion, completing a full cycle every 112,000 years relative to the fixed stars.
I attempted to follow the links and the links to the links in the articles, and no source 100,000 year and 405,000 year orbital cycles were there.
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The 100,000 cycles described by Milankovitch are not cyclic changes in earth’s orbit. They are merely geometric coincidences. Earth’s rotational axis tilts at roughly 23 1/2 degrees. On a 100,000 year timescale the tilt is relatively stable. Earth’s orbit, though mostly circular, still is a couple of percent oval. The major oval orbital axis constantly rotates around the sun, as all oval orbital axes do. The period of this orbital axis rotation is 100,000 years. Currently earth’s orbital axis places earth closest to the sun as the southern hemisphere tilts toward the sun.
Oceans absorb solar radiation far better than continents.
Continents reflect more solar radiations than oceans. The southern hemisphere contains far more ocean than the northern hemisphere, so when the southern hemisphere points at the sun during its orbital closest pass the earth warms. This warming has lasted 10,000 years, and will last another 10,000 years until earth is plunged into another 80,000 year ice age as earth’s orbit points the southern oceans off into space at earth’s annual closest pass to the sun.