An odd potential exists that the collision of Sagittarius and The Milky Way has implications for our weather history. Perhaps even for why our present series of Ice Ages began. I don’t have any mechanism for it, but the time line is rather, er, interesting…
First off, the “backstory” is that we are aliens to The Milky Way. That’s part of why our solar system is at an odd angle to the galactic plane. (Normally spinning things tend to form such that the spin axis stays aligned. Conservation of angular momentum and all that.)
Milky Way’s spiral arms are the product of an intergalactic collision course
UC Irvine models show dark matter packs a punch
— Irvine, Calif., September 14, 2011 —
UC Irvine astronomers have shown how the Milky Way galaxy’s iconic spiral arms form, according to research published today in the journal Nature.
A dwarf galaxy named Sagittarius loaded with dark matter has careened twice through our much larger home galaxy in the past two billion years, according to telescope data and detailed simulations, and is lined up to do it again. As the galaxies collide, the force of the impact sends stars streaming from both in long loops. Those continue to swell with stars and are gradually tugged outward by the Milky Way’s rotation into a familiar ringed arm.
The smaller galaxy pays a steep price though – sucked inward repeatedly by the Milky Way’s mightier gravity, it’s being ripped apart by the blows, sending huge amounts of its stars and dark matter reeling into the new arms.
The Sagittarius galaxy is due to strike the southern face of the Milky Way disk fairly soon, Purcell said – in another 10 million years or so.
Billions of years, millions of years, it’s just “big stuff”… So the first couple of times this went by, I didn’t think much about it. So we were in another galaxy Billions of years ago. Now we’re in The Milky Way. What about things recently? ( Or so my usual line of attention goes…) But look again at what it said:
“twice through our much larger home galaxy in the past two billion years”
So really only about 1 Billion for the last time through. Perhaps even less. If the next one is in just 10 Million (when the bit that was not captured last time returns) that’s 3 times in 2 Billion or about 660 Million years. That’s modestly recent on geologic time scales.
During one of those passes, our solar system got sucked off of Sagittarius and into The Milky Way. Don’t know if it was the first pass ( 2 Billion ) or the second ( 1 Billion to 660 Million) and don’t know what happens to our neighborhood in 10 Million… but it would be interesting to look in our geologic / biologic record for anything “odd” with those dates. 2 MY BP, 1 BY BP, 660 MY BP.
We also don’t know if we got ‘nabbed’ in the first pass, or the second. Or if they are evenly spaced or on a dampening time period for the ‘passes’. So what happened between 1 BY and 660 MY BP?
The parts measured in “Billions” are in the Precambrian. Near as I can tell, it was warm, wet, stable, and not much of interest happening in the first Billion of it.
Looking at geology we find an interesting bit.
Rocks from the earliest well established ice age, called the Huronian, formed around 2.4 to 2.1 Ga (billion years) ago during the early Proterozoic Eon.
So our first major Ice Age started just about the time of the first collision of the two galaxies…
The next, and worst, happens about the time of the second pass through. (I suspect this was the one where we got captured by The Milky Way. It was likely traumatic.)
The next well-documented ice age, and probably the most severe of the last billion years, occurred from 850 to 630 million years ago (the Cryogenian period) and may have produced a Snowball Earth in which glacial ice sheets reached the equator, possibly being ended by the accumulation of greenhouse gases such as CO2 produced by volcanoes. “The presence of ice on the continents and pack ice on the oceans would inhibit both silicate weathering and photosynthesis, which are the two major sinks for CO2 at present.” It has been suggested that the end of this ice age was responsible for the subsequent Ediacaran and Cambrian Explosion, though this model is recent and controversial.
Extinctions are proposed to have affected even life’s earliest organisms. About 650 million years ago, seventy percent of the dominant Precambrian flora and fauna perished in the first great extinction. This extinction strongly affected stromatolites and acritarchs, and was also the predetermining factor that encouraged the diversification of the following Vendian fauna. However, this distinct fauna, resembling modern-day soft-bodied organisms such as sea pens, jellyfish, and segmented worms also perished in a second extinction event at the close of the Vendian. This event, responsible for the demise of the Vendian organisms, may have been reponsible for the ensuing diversification of the Cambrian shelly fauna.
There was another minor Ice Age a bit later, then our present Ice Age (consisting of many Glacial periods) began.
The current ice age, the Pliocene-Quaternary glaciation, started about 2.58 million years ago during the late Pliocene, when the spread of ice sheets in the Northern Hemisphere began. Since then, the world has seen cycles of glaciation with ice sheets advancing and retreating on 40,000- and 100,000-year time scales called glacial periods, glacials or glacial advances, and interglacial periods, interglacials or glacial retreats. The earth is currently in an interglacial, and the last glacial period ended about 10,000 years ago. All that remains of the continental ice sheets are the Greenland and Antarctic ice sheets and smaller glaciers such as on Baffin Island.
Just about the time we’re getting to a few million years to merger, again.
Effectively, we were part of a different galaxy prior to the onset of the Glaciations. Did they have onset about the time our old galaxy was starting to merge with The Milky Way? Was there a significant change in the amount of cosmic rays or interstellar dust? I have trouble believing such an event could happen and not mess them up to some degree. Nor would I expect the Sun to have been unaffected.
It’s also possibly part of why there’s an odd protrusion of stars out of the Galactic Plane near us (and some of the more active and interesting stars at that).
When did our present Ice Age begin?
How far back for the onset of this round of glaciations and interglacials?
Is there a part of the smeared out Sagittarius near here now?
The stage prior to the Calabrian was, for a while, defined as being in a different age. It got moved up a bit. It isn’t typified by a ‘plunge into cold’ so much as by ‘some cold starts’.
The Gelasian was introduced in the geologic timescale in 1998. It is named after the Sicilian city of Gela in the south of the island. In 2009 it was moved from the Pliocene to the Pleistocene in order that the geologic time scale be more consistent with the key changes in Earth’s climate, oceans, and biota that occurred 2.588 million years ago.
The base of the Gelasian is defined magnetostratigraphically as the base of the Matuyama (C2r) chronozone (at the Gauss-Matuyama magnetostratigraphic boundary), isotopic stage 103. Above this point there are notable extinctions of the calcareous nannofossils: Discoaster pentaradiatus and Discoaster surculus. The GSSP for the Gelasian is located at the Monte Sant Nicola near Gela.
The top of the Gelasian is defined magnetostratigraphically as the end of the Olduvai (C2n) chronozone, and faunally as the extinction level of the calcareous nannofossil Discoaster brouweri (base of biozone CN13). Above the Gelasian as the first occurrences of the calcareous nannofossil Gephyrocapsa sp. and the extinction level of the planktonic foraminifer Globigerinoides extremus.
During the Gelasian the ice sheets in the Northern Hemisphere began to grow, which is seen as the beginning of the Quaternary ice age.
So I’m going to posit a ‘wild idea’ here.
About 2.5 to 2 Billion Years Before Present, we were in Sagittarius and just starting the merge process. Things started getting cold. “We” stayed in Sagittarius during this process, but didn’t get far. On ’round two’ we were fully captured by The Milky Way. In the process, we had a plunge into a very cold ice age glacial.
Then about 60 Million years ago a bit of a ‘Hobbit Galaxy’ whacked into the local area making Gould’s Belt. I would speculate it was some ‘left overs’ from the collision of Sagittarius a long ways back. In the process, a couple of fat stars had a very unusual ‘head on’ and gave us that ‘over supernova’ event that formed Gould’s Belt. After that, it quieted down again.
Our local changes mostly dominated by 50-60 Million years of ‘bobbing’ up and down in the local spiral arm area as we settle in.
Things warmed up again.
Then, just a couple of Million years ago, with parts of the Sagittarius galaxy returning, we started a new Ice Age with a new series of glacials.
But in 10 Million years, “something interesting” will happen, again… (That’s way short in evolutionary time scales). The main body of what’s left of the smeared out Sagittarius galaxy returns, for yet more merger mania.
There are some odd things about the evolution of the solar system and Earth that are puzzles. Things like The Faint Young Sun Paradox, for example. Yet in none of those have I seen folks considering what it means to the process if it is NOT a stable and steady evolution; if instead the solar system gets tossed around and the amount of galactic dust and cosmic rays get wildly changed by galactic mergers.
I think that matters.
We didn’t slowly evolve over 5 Billion years in our present place and configuration in The Milky Way. We evolved in an entirely different context. One that is now gone as the Old Sagittarius galaxy got mergered, smearing and stretching in the process.
One other small note. “Something big” happened about the time our solar system was formed, in that long gone Old Sagittarius galaxy.
c. 4,570 Ma: A supernova explosion seeds our galactic neighborhood with heavy elements that will be incorporated into the Earth, and results in a shock wave in a dense region of the Milky Way galaxy. The Ca-Al-rich inclusions, which formed 2 million years before the chondrules, are a key signature of a supernova explosion.
4,567±3 Ma: Rapid collapse of hydrogen molecular cloud, forming a third-generation Population I star, the Sun, in a region of the Galactic Habitable Zone (GHZ), about 25,000 light years from the center of the Milky Way Galaxy.
4,566±2 Ma: A protoplanetary disc (from which Earth eventually forms) emerges around the young Sun, which is in its T Tauri stage.
Spectacular picture of the metallic spherical chondrules inside meteorites here:
Notice a small problem with those first two dates?
Add the margin of error to the second one. You get 4,570 MY BP. Same as the first one…
So how did all the “stuff” travel from ‘far far away’ to get here from that supernova and form the Sun, while zero time passes?
It sure looks to me like some kind of small nova event happened, a lot of ‘stuff’ stayed in the area, and it formed our present sun and solar system. Which would put the center of the ‘bang’, right on top of our Sun. You can have near zero travel time if you have local creation of materials… Without that local creation, there is one heck of a timing problem.