It was in 1775 that Pierre-Simon Laplace developed his theories of tidal dynamics, formulating in the following year a set of equations to explain the phenomenon at a greater level of detail than ever before. Looking at the Moon on a frosty winter night, it’s pleasing to realize that there is a mountainous region at the end of Montes Jura in Mare Imbrium that is called Promontorium Laplace. Surely the French astronomer and mathematician would have been pleased.
One result of Laplace’s calculations was his pointing out that the Moon’s equatorial bulge was far too large to be accounted for by its current rate of rotation. Here we’re dealing with conditions of formation of an object thought to have been the result of a collision between the Earth and a Mars-sized planet early in our system’s evolution. I seldom write about the Moon in these pages, but today’s story on its development catches my eye because it relates to the early history of our own world and the Solar System itself. For Chuan Qin (now at Harvard University) and colleagues have modeled how quickly the hot young Moon receded from the Earth.
The current rate of the Moon’s recession from the Earth is about 4 centimeters per year. But what was the recession rate in the earliest periods of its formation?
Image credit: University of Colorado at Boulder.
The tidal bulge at the equator evidently has much to tell us. A hot, fast-rotating early Moon would have possessed a much larger equatorial bulge than today’s. As the Moon moved farther from the Earth and its rotation slowed, the bulge would have shrunk until, cooled and hardened, a permanent ‘fossil’ bulge remained in its crust. Working with a model adjusting the relative timing of lithosphere thickening and lunar orbit recession, Qin and team have found that the pace of the lunar recession was slow, lasting for several hundred million years in an era roughly four billion years ago.
If this dynamic modeling is correct, it can tell us something about the early Earth, says Shijie Zhong (University of Colorado at Boulder), a co-author on the paper:
“The moon’s fossil bulge may contain secrets of Earth’s early evolution that were not recorded anywhere else. Our model captures two time-dependent processes and this is the first time that anyone has been able to put timescale constraints on early lunar recession.”
The new model has implications for the hydrosphere, the combined mass of water on the early Earth. The researchers argue that the Moon’s equatorial bulge is evidence that Earth’s energy dissipation in response to tidal forces would have been greatly reduced in this period. That’s assuming that a hydrosphere even existed in the Hadean, a geologic eon that began with the planet’s formation some 4.6 billion years ago and ended roughly 4 billion years ago. From the paper:
Viable solutions indicate that lunar bulge formation was a geologically slow process lasting several hundred million years, that the process was complete about 4 Ga when the Moon-Earth distance was less than ~32 Earth radii, and that the Earth in Hadean was significantly less dissipative to lunar tides than during the last 4 Gyr, possibly implying a frozen hydrosphere due to the fainter young Sun.
The paper makes the case that Earth’s hydrosphere may have been frozen during the time of the Moon’s formation, making for little tidal dissipation. One possibility emerging from that is a faint young Sun radiating about 30 percent less energy than today. A ‘snowball Earth’ in the Hadean could have been the result, but we have no direct evidence in the geological record for this. Qin and team intend to continue work on their model as they dig deeper into the Moon’s evolution in a period ending with the Late Heavy Bombardment some 3.8 billion years ago.
The paper is Qin et al., “Formation of the Lunar Fossil Bulges and Its Implication for the Early Earth and Moon,” Geophysical Research Letters 2 February 2018 (abstract).
Hadean zircon and greenstone belts like the Isua and Nuvvuagittuq have shown that the Earth had a substantial liquid hydrosphere during the period in question. A 2016 paper from Carl Wunsch at MIT suggested that a global ice shield at least of the strength speculated in the proterozoic Snowball Earth phase would not have had a devastating effect on tidal dissipation. https://www.google.de/url?q=http://ocean.mit.edu/~cwunsch/papersonline/tides_ice_cover_icarus2016.pdf
With no access to the paper from Qin et al. I wonder about the degree of freezing that is hypothesized therein.
wasn’t the Hadean named after Hades ie Hell? Wasn’t the surface supposed to be molten?
Interesting. more support for the large impact hypothesis.
The paper’s math is way over my head, but the constraints on the Hadean Earth’s surface have consequences.
If, as the authors’ suggest, the Hadean Earth was in a snowball state needed to reduce tidal dissipation, then life’s genesis must have been extremely fast at the end of this period (4 gya) to result in fossils 3.5 gya and possibly even as early as 3.8 gya. This suggests to me that life would have started in the ocean depths at vents that were erupting below the surface ice.
A snowball Earth in the Hadean seems to obviate any need for a warm surface maintained by CO2, CH4 and possibly H2 for the necessary greenhouse effect with a faint sun.
Another possibility is that the oceans were largely absent during the Hadean, perhaps being created by cometary impacts. But if that is the case, then the genesis would be similarly constrained in time to models of life evolving in “warm ponds” on the surface. Which may, in turn, lend credence to the panspermia theory, perhaps originating on Mars or outside the solar system.
Then again, maybe the authors’ models are wrong about the lunar bulge despite the claimed robustness of the variables to the result.
I don’t believe the continents had formed yet so tidal dissipation would have been weak as there was no significant land masses to interact with. Any land masses that would have formed would have been weakly held up as well due to the higher ground temperature.
I wouldn’t jump to conclusions. Life that began without any light has yet to be proven. The thermophiles in our sea migrated there from the surface. Sunlight might have been needed for it too start but even if it didn’t sunlight is still needed for photosynthesis. This theory hypothesizes that UV radiation began life: http://www.sciencemag.org/news/2017/07/how-sunlight-might-have-jump-started-life-earth
The speculation on temperatures of Hadean Earth (and early Mars) assume implicitly that they were the same distance from the Sun as now. Maybe not so: The Grand Track model and the Nice model of solar system evolution have Jupiter, Saturn, Uranus and Neptune migrating in and out. I think we can assume that the inner planets were also affected. To my point: maybe Earth and Mars have also migrated outward. At 4 Gya Earth could have been sufficiently closer that solar flux was comparable to today’s.
How can we find out if the planets of the Sol system were in different orbits 4 billion years ago?
We have only indirect ‘evidence’, such as that the models explain the Late Heavy bombardment, and that for Mars in its present position to have liquid water despite the weak Sun, one must assume a thick CO2 atmosphere supplemented with methane (from where?, I ask) https://en.wikipedia.org/wiki/Mars_ocean_hypothesis#Primordial_Martian_climate
I have the feeling, that the lunar spin, could have reversed the present 4cm per year retreat, by spin of moon reduction, while close during hadean times, by spinning tidal reduction of lunar surface, thus masking earth hydrological tidal retardation. Thus the reduction of lunar angular momentum, reversed the tidal retardation of lunar distance, but not earth spin reduction, which also carried on, much stronger then, thus spinning faster during the early hadean, and reducing day length more rapidly.
Talking of cold planets in the early solar system, there are some recent results on Martian clays that suggest a cold climate for ancient Mars, with only sporadic warm periods (possibly triggered by impacts).
One interesting aspect of this entire conversation is the fact that I believe most people are unaware that the orbital mechanics of the Moon-Earth system is gravitationally coupled so strongly that there has been since the formation of the system a tremendous amount of angular momentum transfer between the two bodies.
A very brilliant nineteenth century mathematician by the name of G. W. Hill was among the first to show mathematically that the moon will undergo a constant regression in distance from the earth, but eventually it will have a maximal limit which due to the physics will put a On how far out the moon can ultimately recede to.
One of the interesting results of this is that ultimately that total eclipses, such as we saw last August in 2017, will cease to occur in about 600 million years and there will be only annular eclipses. After that, on earth. The mechanics of these angular momentum transfers are extremely interested in the way that they effect the spin of the planet and also to the seasons that life depends on here on earth.
Charlie, when you say most people you must mean the layman because the gravitational coupling of the Earth Moon system is planetology 101 in most universities. It was explained in my junior college Moons and Planets book by William K. Hartmann 1983 version. Also in The Realm of the Terrestrial Planets, Znenek Kopal. You are right about the angular momentum which was supplied by the the collision of Theia in the Giant Impact hypothesis. The spin couldn’t reverse itself since it has to start with more angular momentum or faster spin. Also there is also fossil evidence of that there were shorter days, 21 hours in the Cambrian 500 million years ago and more days in the year like 400; the evidence comes from the shells of scallops with 400 lines for days, much longer shoreline tidal movement and etc.
The friction of the sea on the Earth slows down its rotation and causes the rotational momentum of the Earth to be transferred to the orbital momentum of the Moon. The tides of the Moon still slow down the rotation of the Earth even without a liquid sea but the slowing will still be less without a liquid sea or with a frozen sea, but the Moon bulge hypothesis is valid.
Pardon me for the mistake. The other book I read with the gravitation coupling of the Earth-Moon system was called “Exploration of the Universe by George O. Abell. 1982 version, which was the astrophysics textbook for the junior college I attended.
February 2018
Ocean tides could have driven ancient fish to walk
Evolution of land-walking animals may have started with fish that were stranded in tidal pools.
Alexandra Witze
http://www.nature.com/articles/d41586-018-02034-w
A new view of the Moon
Research led by grad student points to origins in ‘synestia,’ challenging widely accepted model.
By Peter Reuell – Harvard Staff Writer
Date March 2, 2018
Simon Lock wants to change the way you think about the moon.
A graduate student in Harvard’s Department of Earth and Planetary Sciences, Lock is the lead author of research that challenges mainstream thought by suggesting that the moon emerged from a massive, doughnut-shaped cloud of vaporized rock called a synestia. The study was published this week in the Journal of Geophysical Research: Planets.
“The commonly accepted theory as to how the moon was formed is that a Mars-size body collided with the proto-Earth and spun material into orbit,” Lock said. “That mass settled into a disk and later accreted to form the moon. The body that was left after the impact was the Earth. This has been the canonical model for about 20 years.”
It’s a compelling story, Lock said, but probably wrong.
The full story here:
https://news.harvard.edu/gazette/story/2018/03/new-origin-story-for-moon-in-harvard-led-research/
Changes in Earth’s orbit could explain rise and fall of ancient species
June 9, 2018
New research published in Proceedings of the National Academy of Sciences looks back 450 million years to reveal an important link between changes in our planet’s motion through space, and the extinction and evolution of life on Earth.A team of researchers, including paleontologist Michael Foote at the University of Chicago, examined the fossils of graptoloids, an extinct type of plankton that floated in ancient oceans. They found evidence that regular changes in the Earth’s orbit and axis of rotation caused significant changes in both the evolution and extinction rates of these creatures.
“This research is very exciting because the relationship between these orbital changes and extinction has never been shown before in truly ancient ecosystems,” said Prof. James Crampton of Victoria University of Wellington, who led the study. “There’s a strong debate in science about the impact on extinction and evolution of environmental change versus interactions between species (such as competition for food). With this study we can provide evidence of the impact of environmental changes on life on Earth.”
Full article here:
https://scienceblog.com/501422/changes-in-earths-orbit-could-explain-rise-and-fall-of-ancient-species
To quote:
“This kind of cyclicity has been difficult to document in such ancient records—that is, going back hundreds of millions of years rather than hundreds of thousands,” said Foote, a professor of geophysical sciences at the University of Chicago and a co-author on the paper.
The analysis was possible due to the extensive fossil graptoloid dataset developed by New Zealand’s GNS Science and the University of California-Riverside, researchers said. It covers the entire globe, and the average resolution in the record is about 40,000 years, rather than the multiple millions that Foote is used to dealing with. “As exciting as this result is, I’m equally excited for the potential for other studies that one could do with the fabulous level of detail in this dataset,” he said.
Citation: “Pacing of Paleozoic macroevolutionary rates by Milankovitch grand cycles,” Crampton et al, Proceedings of the National Academy of Sciences, USA May 15, 2018. DOI: 10.1073/pnas.1714342115