Artist's impression.
Oliver Hull
I know I'm always writing about things that happened before creationism's mythical 'Creation Week', but the problem is, almost everything that happened happened then. 99.9975% of Earth's history happened then, for example, and far more of the Universe's, since the Universe is some 3-4 times as old as Earth and an awful lot happened between the Big Bang and the formation of the sun and its planetary system.
And so, true to form, this is about the time 466 million years ago, when, according to the findings of three researchers from Monash University, Melbourne, Victoria, Australia, led by Professor Andrew G. Thomkins, Earth had a ring system, somewhat like those of Jupiter and Saturn. They believe the ring was composed of the debris of a large asteroid that passed close enough to Earth to be broken up by gravitational tidal forces.
The result was a sudden plunge into an ice age and a period of intense bombardment with meteorites lasting millions of years and producing an otherwise difficult to explain pattern of impact craters.
A recent theory proposes a ring system round Earth formed by a disintegrated large asteroid, could have caused the Hirnantian Icehouse* What exactly is that, and how could a ring of debris have caused it? The Hirnantian Icehouse refers to a significant global cooling event that occurred at the end of the Ordovician Period, about 445-443 million years ago. It resulted in widespread glaciation, particularly in the southern hemisphere, and was accompanied by a major mass extinction event—the second largest in Earth's history. This extinction wiped out about 85% of marine species, including many trilobites, brachiopods, and corals.
The Ring System Hypothesis
A recent theory suggests that a ring system around Earth, formed by the disintegration of a large asteroid, could have been the cause of this glaciation. Here’s how it might have worked:
While this is an intriguing idea, more evidence is required* to confirm if such a ring system truly existed and played a direct role in triggering the Hirnantian Icehouse.
- Asteroid Disintegration: The theory posits that a large asteroid, upon approaching Earth, was torn apart by tidal forces or a massive collision. The debris from this asteroid may have formed a temporary ring system around the planet, similar to the rings of Saturn.
- Reduced Solar Radiation (Albedo Effect): If this ring was dense enough, it could have partially blocked or reflected sunlight away from the Earth’s surface. This would have increased Earth's albedo (the reflectivity of the planet), causing less solar energy to reach the surface. The reduced solar radiation could have led to a global cooling, triggering the Hirnantian glaciation.
- Geographic Impact on Glaciation: The icehouse phase coincided with the positioning of the southern supercontinent Gondwana over the South Pole, which facilitated the buildup of ice sheets. The presence of the ring system could have further accelerated this process by cooling the planet beyond natural climate cycles.
- Dust and Atmospheric Changes: The disintegration of the asteroid would have added large amounts of dust and debris to the atmosphere, compounding the cooling effect. Atmospheric particles reflect sunlight and can lead to a "nuclear winter"-like cooling, which may have also played a role.
- Short-Term vs. Long-Term Effects: It’s important to note that the Hirnantian Icehouse lasted only a few million years, after which the climate returned to warmer conditions. If this ring system hypothesis holds true, the debris might have dissipated or fallen to Earth over time, allowing sunlight to once again reach the surface and warm the planet.
In the context of a disintegrating asteroid, what is Earth's Roche Limit?
The Roche limit is the minimum distance at which a celestial body, such as a moon or an asteroid, can approach a larger body (like a planet) without being torn apart by the larger body’s tidal forces. For Earth, this limit is relevant in the context of a disintegrating asteroid or other objects that come close enough to be affected by its gravitational pull.
Tidal Forces and the Roche Limit
When a smaller body (like an asteroid) comes within a certain distance of a planet, the planet’s gravitational pull on the side of the asteroid closer to it is much stronger than on the far side. These differing forces are called tidal forces, and they can cause the object to stretch and eventually break apart if it gets too close to the planet.
- If the asteroid or moon is held together only by gravity (a rubble-pile asteroid, for instance), the tidal forces from Earth will overcome the object’s own gravity and pull it apart.
- The Roche limit depends on the densities of both the planet and the approaching object. For a rigid body (one held together by its internal strength), the Roche limit is smaller than for a fluid or loosely held-together object.
Earth’s Roche Limit
For a typical object with a density similar to many moons or asteroids (about the same density as water), Earth’s Roche limit is roughly 18,000 kilometers (11,200 miles) from the Earth's center. If an asteroid crosses inside this limit, tidal forces from Earth can tear it apart, potentially forming a ring system from the debris.
Relevance to the Disintegrating Asteroid Hypothesis
If the theory suggesting that a disintegrating asteroid could have caused a temporary ring system around Earth is correct, the asteroid likely crossed inside Earth's Roche limit, was broken apart by tidal forces, and its debris began orbiting the planet. This material could have coalesced into a ring, temporarily blocking sunlight and contributing to global cooling, such as the one theorized for the Hirnantian Icehouse.
The Monash University team have just published their findings, open access, in the journal Earth and Planetary Science Letters. They explain it in a Monash University News release:
Earth may have had a ring system 466 million years ago
In a discovery that challenges our understanding of Earth’s ancient history, researchers have found evidence suggesting that Earth may have had a ring system, which formed around 466 million years ago, at the beginning a period of unusually intense meteorite bombardment known as the Ordovician impact spike.
This surprising hypothesis, published today in Earth and Planetary Science Letters, stems from plate tectonic reconstructions for the Ordovician period noting the positions of 21 asteroid impact craters. All these craters are located within 30 degrees of the equator, despite over 70 per cent of Earth’s continental crust being outside this region, an anomaly that conventional theories cannot explain.
The research team believes this localised impact pattern was produced after a large asteroid had a close encounter with Earth. As the asteroid passed within Earth’s Roche limit, it broke apart due to tidal forces, forming a debris ring around the planet—similar to the rings seen around Saturn and other gas giants today.
Over millions of years, material from this ring gradually fell to Earth, creating the spike in meteorite impacts observed in the geological record. We also see that layers in sedimentary rocks from this period contain extraordinary amounts of meteorite debris. What makes this finding even more intriguing is the potential climate implications of such a ring system.
Professor Andrew G Tomkins, lead author
School of Earth, Atmosphere and Environment
Monash University, Melbourne, Victoria, Australia.
The researchers speculate that the ring could have cast a shadow on Earth, blocking sunlight and contributing to a significant global cooling event known as the Hirnantian Icehouse.
This period, which occurred near the end of the Ordovician, is recognised as one of the coldest in the last 500 million years of Earth’s history.
The idea that a ring system could have influenced global temperatures adds a new layer of complexity to our understanding of how extra-terrestrial events may have shaped Earth’s climate.
Professor Andrew G Tomkins.
Normally, asteroids impact the Earth at random locations, so we see impact craters distributed evenly over the Moon and Mars, for example. To investigate whether the distribution of Ordovician impact craters is non-random and closer to the equator, the researchers calculated the continental surface area capable of preserving craters from that time.
They focused on stable, undisturbed cratons with rocks older than the mid Ordovician period, excluding areas buried under sediments or ice, eroded regions, and those affected by tectonic activity. Using a GIS approach (Geographic Information System), they identified geologically suitable regions across different continents. Regions like Western Australia, Africa, the North American Craton, and small parts of Europe were considered well-suited for preserving such craters. Only 30 per cent of the suitable land area was determined to have been close to the equator, yet all the impact craters from this period were found in this region. The chances of this happening are like tossing a three-sided coin (if such a thing existed) and getting tails 21 times.
The implications of this discovery extend beyond geology, prompting scientists to reconsider the broader impact of celestial events on Earth’s evolutionary history. It also raises new questions about the potential for other ancient ring systems that could have influenced the development of life on Earth.
Could similar rings have existed at other points in our planet’s history, affecting everything from climate to the distribution of life? This research opens a new frontier in the study of Earth’s past, providing new insights into the dynamic interactions between our planet and the wider cosmos.
Highlights
- Earth may have had a ring during the middle Ordovician, from ca. 466 Ma.
- Breakup of an asteroid passing within Earth's Roche limit likely formed the ring.
- Among several features preserved is a near-equatorial band of impact craters.
- Shading of Earth by the ring may have triggered a global icehouse period.
Abstract
All large planets in our Solar System have rings, and it has been suggested that Mars may have had a ring in the past. This raises the question of whether Earth also had a ring in the past. Here, we examine the paleolatitudes of 21 asteroid impact craters from an anomalous ∼40 m.y. period of enhanced meteor impact cratering known as the Ordovician impact spike and find that all craters fall in an equatorial band at ≤30°, despite ∼70 % of exposed, potentially crater-preserving crust lying outside this band. The beginning of this period is marked by a large increase in L chondrite material accumulated in sedimentary rocks at 465.76 ± 0.30 Ma, which, together with the impact spike, has long been suggested to result from break-up of the L chondrite parent body in the asteroid belt. Our binomial probability calculation indicates that it is highly unlikely that the observed crater distribution was produced by bolides on orbits directly from the asteroid belt (P = 4 × 10–8). We therefore propose that instead, a large fragment of the L chondrite parent body broke up due to tidal forces during a near-miss encounter with the Earth at ∼466 Ma. Given the longevity of the impact spike and sediment-hosted L chondrite debris accumulation, we suggest that a debris ring formed after this break up event, from which material deorbited to produce the observed crater distribution. We further speculate that shading of Earth by this ring may have triggered cooling into the Hirnantian global icehouse period.
1. Introduction
Interactions between the Earth and incoming materials from the Solar System have dramatically influenced the evolution of life on Earth, well exemplified by the extinction of the dinosaurs caused by the Chicxulub impact event (Alvarez et al., 1980; Hildebrand et al., 1991; Kring and Boynton, 1992). Unique in at least the last 540 m.y. (the period for which there are data; Terfelt and Schmitz, 2021), was a dramatic increase in the impact cratering rate and flux of meteorite material to Earth starting in the mid-Ordovician and extending for perhaps as much as 40 m.y. (Fig. 1; Liao et al., 2020; Martin et al., 2018; Osinski et al., 2022; Schmieder and Kring, 2020.1; Terfelt and Schmitz, 2021), although the duration is presently poorly constrained. The beginning of this period is recorded in limestone, at multiple places around the world, recognised by a 2–3 order of magnitude enrichment in L chondrite meteorite and micrometeorite debris (Martin et al., 2018; Schmitz et al., 2022.1, 2001; Terfelt and Schmitz, 2021). A coincident period of enhanced seismic and tsunami activity, recognised through globally distributed megabreccia deposits, may be related (Parnell, 2009); although an alternative has been suggested by (Meinhold et al., 2011). This event may have promoted the Great Ordovician Biodiversification Event (Schmitz et al., 2008), after triggering a global icehouse (Schmitz et al., 2019). Deposition of L chondrite material in limestones at this time was suggested to have been caused by an increase in asteroid dust dispersed throughout the inner Solar System after impact-associated break-up of an L chondrite parent body (LCPB) within the asteroid belt (Schmitz et al., 2008, 2001). We hypothesise that instead, a large L chondrite asteroid had a near-miss encounter with the Earth at about 466 Ma, passing within the Roche limit, which caused the body to break-up and form a debris ring.
Fig. 1. Age estimates of the currently recognised Ordovician impact spike craters (Parisi et al., 2024; Schmieder and Kring, 2020.1), overlain on the estimated period of anomalous extraterrestrial chromite accumulation in sediments (Terfelt and Schmitz, 2021), and the known period of seismic/tsunami-induced megabreccia deposits (Parnell, 2009). The blue line indicates the global average temperature prior to 1990 (Martin et al., 2018; Schmitz et al., 2022.1; Scotese, 2021.1; Terfelt and Schmitz, 2021).
To investigate the possibility of a ring-forming event in the mid-Ordovician, we examined the paleolatitude positions (based on six tectonic plate reconstruction models; Domeier, 2016, 2018.1; Merdith et al., 2021.2; Scotese, 2016.1; Torsvik and Cocks, 2016.2; Torsvik et al., 2014) of the 21 meteorite impacts known to coincided with the enhanced Ordovician meteorite flux. The beginning of the period of interest is considered to be precisely defined by the age of volcanic ash layers in the meteorite-rich limestone at Thorsberg Quarry in Sweden, at 465.76 ± 0.30 Ma (Liao et al., 2020). The duration of the period of time from that point is poorly constrained, but is based on the observation that there is still above background L chondrite flux preserved in the geological record 40 m.y. later (Martin et al., 2018; Terfelt and Schmitz, 2021). We then calculated the probability that the observed crater positions resulted from randomly distributed impact events across the globe, which would be expected if all impactors were derived from orbits in the asteroid belt (Rumpf et al., 2016.3), but not if they were derived from a single body that broke up during a close encounter with the Earth.
[…]
4. Summary and conclusions
We have suggested that a large L chondrite asteroid had a near miss encounter with Earth at ca. 466 Ma, which caused it to break up as it passed through Earth's Roche limit. This can explain why sedimentary rocks from this time contain 99 % L chondrite material at abundances 2–3 orders of magnitude above background, with extremely brief CRE ages. We have further suggested that the resulting fragments formed a debris ring that decayed over several tens of millions of years resulting in an anomalous spike in impact cratering rate. This hypothesis may explain why all impact structures from this time are located proximal to the equator; impacts from bodies originating in the asteroid belt are expected to be randomly distributed across the globe. We have estimated the probability that this impact structure distribution resulted from random unrelated impactors at 1 in 25 million. We speculate that this ring may have promoted the coldest global cooling event in the last 540 million years, the Hirnantian Icehouse period.
Tomkins, Andrew G.; Martin, Erin L.; Cawood, Peter A.
Evidence suggesting that earth had a ring in the Ordovician
Earth and Planetary Science Letters (2024) 646 118991 DOI: 10.1016/j.epsl.2024.118991
Copyright: © 2024 The authors.
Published by Elsevier Ltd. Open access.
Reprinted under a Creative Commons Attribution 4.0 International license (CC BY 4.0)
Creationists like to claim, despite the abundant evidence to the contrary, that we live in a 'Goldilocks' zone on a planet in a universe carefully and intelligently designed for life.
What this team of scientists have found gives the lie to that claim as it shows how precarious Earth's ecosystems are if a random asteroid, of which there is a plentiful supply orbiting the sun, can plunge earth into a very hostile place, and set of another mass extinction even if it doesn't score a direct hit. A repetition of this event would almost certainly include the extinction of humans and our livestock.
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