© nternational Centre for Global Earth Models/Wikimedia, CC BY 4.0Geoid undulation in false color.
Gravity's pull is a constant on Earth, but
our planet is no uniform sphere. It's covered in lumps and bumps, with geology of varying density yanking on nearby masses with subtly differing degrees of force in an
undulating map known as a geoid.
Deep beneath the Indian Ocean, that pull weakens to an extreme low, leaving what is considered a massive gravity 'hole' some three million square kilometers in size roughly where the seafloor sinks into a vast depression.One of the most profound gravitational anomalies on Earth, its presence has been alluded to for a while. Ship-based surveys and satellite
measurements revealed long ago that the sea level just off the tip of the Indian subcontinent dipped on account of the gravitational tug-of-war between the aptly named Indian Ocean geoid low and the surrounding gravitational 'highs'.
Just what caused this relative weakening has never been clear. Now two researchers from the Indian Institute of Science think they have a better idea of the kinds of planetary phenomena that could be involved.
"All these [past] studies looked at the present-day anomaly and were not concerned with how this geoid low came into existence," geoscientists Debanjan Pal and Attreyee Ghosh
explain in their published paper, which describes their new working hypothesis.
They think the answer lies more than 1,000 kilometers (621 miles) beneath Earth's crust, where the cold, dense remnants of an ancient ocean plunged into a 'slab graveyard' beneath Africa some 30 million years ago, stirring up hot molten rock.But their results, based on computer models, are unlikely to settle a fiery debate about the geoid low's origins - at least not until more data is collected.
In 2018, a shipload of scientists from India's National Centre for Polar and Ocean Research
set out to deploy a string of seismometers along the seafloor of the deformation zone, to map the area.
Being so far offshore, little seismic data had been collected in the area before. The results from that
2018 survey pointed to the presence of hot plumes of molten rock rising up beneath the Indian Ocean and somehow contributing to its great dent.
© Ningthoujam, Negi & Pandey/EOS, 2019The gravitational 'hole' in the Indian Ocean, and the location of seismometers (black triangles) deployed on the seafloor.
But a longer view was needed to reconstruct the geoid low in its early phases. So Pal and Ghosh retraced the formation of the massive geoid by modeling how tectonic plates skimmed over Earth's
hot, gooey mantle during the past 140 million years.
Back then, the
Indian tectonic plate was just starting to break away from the supercontinent, Gondwana, to begin its northward march. As the Indian plate advanced, the seabed of
an ancient ocean called the Tethys Sea sank into Earth's mantle, and the Indian Ocean opened up behind it.
Pal and Ghosh ran simulations
using more than a dozen computer models of plate motion and mantle movements, comparing the shape of the oceanic low those models predicted with observations of the dent itself.
The models that reproduced the Indian Ocean geoid low in its current form
all had one thing in common: plumes of hot, low-density magma wafting up beneath the low. These plumes, in addition to a distinctive mantle structure, are what created the geoid low; if they rise high enough, Pal and Ghosh
surmise.
"In short, our results suggest that to match the [shape and amplitude of the] observed geoid low, plumes need to be buoyant enough to come up to mid-mantle depths," the pair
writes.
The first of these plumes appeared about 20 million years ago, to the south of the Indian Ocean geoid low, and around 10 million years after the old Tethys Sea sank into the lower mantle. As the plumes spread beneath the
lithosphere and inched towards the Indian peninsula, the low intensified.
Given their results are consistent with elements of Ghosh's
previous modeling work from 2017, the duo
suggests the telltale plumes were thrust up after the Tethys seafloor sank into the lower mantle, disturbing the famed 'African blob'.However, some researchers not involved in the work
aren't convinced, telling
New Scientist there isn't any clear seismographic evidence yet that the simulated plumes are actually present beneath the Indian Ocean.
Such data may soon come to light, and there's no rush really - the geoid low is
expected to persist for many more millions of years yet.
The study has been published in
Geophysical Research Letters.
Reader Comments
If my memory serves, me he gave the explanation of how the Moon was a part of the earth, in the creation of the earth, part of the Earth was separated in a cataclysmic change...Many have wondered why the moon only shows one face to the earth...Makes me wonder.
I had it saved on an a much older computer, which crashed, and had to get it replaced, no information was able to be retrieved.
Just a thought, but I do remember, and have tired to search the information again and again, , all that comes up the traditional information regarding the moon, but I have always wondered, if this was real and the truth, maybe Gurdjieff, knew more about reality than has ever been published.
Might it be that "gravity" is not the force it is assumed to be, and is not proportional to mass ?
Could it be then, that this "gravity hole" is caused by something else ?
Perhaps you need to look for a "gravity bump" on the opposite side of the earth ?
It may be that the geology was 'tailored' to fit beliefs, perhaps the Deccan traps are far more recent than claimed and the reacting minerals that created and exuded those granites came from such a depth that they had a different angular momentum to the island, turning it through 180deg. and due to it's slower tangential inertia, once surfaced, forced it north to collide with mainland Asia?
This area is a signpost, one that cannot be read correctly, at least for now.
It will likely unfold into a scenario that academia is ill prepared for and will not bode well for mankind.
[Link] Burckle Crater Impact and Mega-tsunami -Cosmography101 class 18.2 excerpt w/ Randall Carlson 2008
And also this
[Link] Holocene Impacts & Burckle Crater Initial Reporting โCosmography101-5.1 w/ Randall Carlson (Nov โ06)
It seems to me that certain location within the earth, have attractor impacts, meaning, they will strike in the same location over periods of time.
The Cycle of Cosmic catastrophes / R Firestone, etal, is interesting reading and seems to have stood the test of time with other researchers finding support in the 'black mats.'
This theory is in support of a nearby stellar flare from the primary suspect Geminga.
While mass is a parameter of the gravity of an object, its total area is the determining factor. Ref The Gravitational Force of the Sun 1993; The Dance of the Moon 2015 by Pari Spolter,