Explaining dramatic planetwide changes after world’s last ‘Snowball Earth’ event | UW News
These panels show the new theory for the three phases that ended the Snowball Earth event. In the first stage, thick ice sheets separate most of the atmosphere and ocean. In the second stage, freshwater flows into the ocean to join meltwater floating on the ocean’s surface. In the final stage, ocean mixing resumes, allowing exchanges between the atmosphere, upper ocean and deep ocean.
A major theme of the creationist superstition is the childish notion that Earth was perfectly designed for life (and their life in particular because the designer created it all for them).
This of course, as with so much else in creationism, requires a genuine or contrived ignorance of the real world outside their small part of it, or they might notice that large parts of Earth are very hostile to most forms of life, especially multicellular life, and are inhabited, if at all, only by a few extremophile single-celled organisms such as bacteria, archaea and simple algae. Human life is impossible without special equipment at the poles, in deserts, at the top of higher mountains and in the oceans, for example. In fact, the proportion of Earth that is habitable by humans without clothing and shelter is very small indeed.
And there have been times in the past, in that long period of Earth's history that occurred before creationism's mythical 'Creation Week' in which a magic man made of nothing made everything else out of nothing, when Earth was uninhabitable by anything more complex than bacteria and archaea that could life in the depths of the oceans, because Earth was encased in a coating of ice up to 1 Km (0.6 miles) thick, in what is called 'snowball Earth' when the northern and southern icecaps extended until they met at the equator, making terrestrial life impossible.
What are 'cap carbonates' and what is their significance to the study of Earth's geological history? Cap carbonates are distinctive sedimentary rock layers, typically composed of limestone or dolostone, that are often found directly above glacial deposits, especially those linked to ancient ice ages. These layers form immediately following periods of intense global glaciation, such as during the Snowball Earth events in the Precambrian era, specifically the Cryogenian period (~720 to 635 million years ago).These periods came to an end very suddenly, on a geological time scale, and left their mark in the geological column in the form of 'cap carbonates' - limestone deposits when dissolved Carbon dioxide (CO2) precipitated out in the form of calcium carbonate (CaCO3) and magnesium carbonate (MgCO3).
Key Characteristics:
- Composition: Predominantly made up of calcium carbonate (CaCO₃) or magnesium carbonate (dolomite).
- Location: They are found on continental margins or shallow marine environments.
- Thickness: Cap carbonates can be several meters thick and are often found globally distributed, signaling widespread processes.
Significance in Earth's Geological History:
In summary, cap carbonates provide critical evidence of how the Earth's climate system has shifted dramatically in the past, especially after global glaciations. Their presence helps geologists piece together ancient climate models, the carbon cycle, and the early evolution of life.
- Post-glaciation Evidence:
Cap carbonates are crucial indicators of the transition from a global icehouse (glaciated Earth) to a greenhouse (warm Earth) state. Their presence above glacial deposits (tillites) suggests rapid environmental change and warming following these intense ice ages.- Climate Feedback and CO₂ Accumulation:
During Snowball Earth periods, it is hypothesized that the Earth was largely or entirely frozen over, significantly reducing carbon dioxide removal by weathering. Volcanic activity would continue emitting CO₂, leading to a massive build-up of greenhouse gases. When the ice finally melted, this excess CO₂ would cause a rapid and intense warming of the planet, leading to the precipitation of cap carbonates in the newly warm, shallow oceans.- Oxygenation of the Atmosphere and Life Evolution:
The formation of cap carbonates marks a critical point in Earth's oxygenation. This warming period after glaciation could have contributed to the eventual rise of more complex life forms and the second major oxygenation event. The transition from Snowball Earth conditions to warmer climates created environments that were conducive to the expansion of early multicellular life, setting the stage for the Cambrian explosion.- Ocean Chemistry Changes:
The precipitation of cap carbonates indicates drastic changes in ocean chemistry. As ice melted, freshwater influx and the increased availability of carbonate ions due to CO₂ accumulation led to carbonate precipitation in large quantities, altering marine chemistry and sedimentation patterns.
Now two geologists at The University of Washington, Seattle, have provided an explanation for the production of these cap carbonates which factors in seafloor weathering and churning which would have increased the amount of calcium ions (Ca++) in the upper layers of the oceans. Their findings have recently been published, open access, in Nature Communications and are explained in a Washington University News release by Hannah Hickey:
Explaining dramatic planetwide changes after world’s last ‘Snowball Earth’ event
Some of the most dramatic climatic events in our planet’s history are “Snowball Earth” events that happened hundreds of millions of years ago, when almost the entire planet was encased in ice up to 0.6 miles (1 kilometer) thick.
These “Snowball Earth” events have happened only a handful of times and do not occur on regular cycles. Each lasts for millions of years or tens of millions of years and is followed by dramatic warming, but the details of these transitions are poorly understood.
New research from the University of Washington provides a more complete picture for how the last Snowball Earth ended, and suggests why it preceded a dramatic expansion of life on Earth, including the emergence of the first animals.
The study recently published in Nature Communications focuses on ancient rocks known as “cap carbonates,” thought to have formed as the glacial ice thawed. These rocks preserve clues to Earth’s atmosphere and oceans about 640 million years ago, far earlier than what ice cores or tree rings can record.
A person looks at cap carbonate rocks in South China in 2019. The new study provides a new explanation for dramatic global environmental changes that led to their formation.Yarong LiuCap carbonates contain information about key properties of Earth’s atmosphere and ocean, such as changing levels of carbon dioxide in the air, or the acidity of the ocean. Our theory now shows how these properties changed during and after Snowball Earth.
Trent B. Thomas, lead author
Department of Earth and Space Sciences
University of Washington, Seattle, WA, USA.
Cap carbonates are layered limestone or dolomite rocks that have a distinct chemical makeup and today are found in over 50 global locations, including Death Valley, Namibia, Siberia, Ireland and Australia. These rocks are thought to have formed as the Earth-encircling ice sheets melted, causing dramatic changes in atmospheric and ocean chemistry and depositing this unique type of sediment onto the ocean floor.
They are called “caps” because they are the caps above glacial deposits left after Snowball Earth, and “carbonates” because both limestone and dolomite are carbon-containing rocks. Understanding their formation helps explain the carbon cycle during periods of dramatic climate change. The new study, which models the environmental changes, also provides hints about the evolution of life on Earth and why more complex lifeforms followed the last Snowball Earth.
Life on Earth was simple — in the form of microbes, algae or other tiny aquatic organisms — for over 2 billion years leading up to Snowball Earth. In fact, the billion years leading up to Snowball Earth are called the ‘boring billion’ because so little happened. Then two Snowball Earth events occurred. And soon after, animals appear in the fossil record.
Professor David C. Catling, senior author
Department of Earth and Space Sciences
University of Washington, Seattle, WA, USA.
The new paper provides a framework for how the last two facts may be connected.
The study modeled chemistry and geology during three phases of Snowball Earth. First, during Snowball Earth’s peak, thick ice encircling the planet reflected sunlight, but some areas of open water allowed exchange between the ocean and atmosphere. Meanwhile frigid seawater continued to react with the ocean floor.
Eventually, carbon dioxide built up in the atmosphere to the point where it trapped enough solar energy to raise global temperatures and melt the ice. This let rainfall reach the Earth, and let freshwater flow into the ocean to join a layer of glacial meltwater that floated over the denser, salty ocean water. This layered ocean slowed down ocean circulation. Later, ocean churning picked up, and mixing between the atmosphere, upper ocean, and deep ocean resumed.
Future research will explore how pockets of life that may have survived the tumult of the Snowball Earth and its aftermath could have evolved into the more complex lifeforms that followed soon after.We predict important changes in the environment as Earth recovered from the Snowball period, some of which affected the temperature, acidity and circulation of the ocean. Now that we know these changes, we can more confidently figure out how they affected Earth’s life.
Trent B. Thomas.
AbstractThose creationists about to invoke the 'all the dating methods are wrong/forged/made up/ignore the 'fact' that radioactive decay rates use to be much higher' excuse for dismissing this sort of data, might like to consider the fact that most of the dating of the cap carbonates was done using the U/Pb method, which is about the most accurate method available. This dates the rock formation to about 634 million years old give or take a million, so an explanation of such a discrepancy between 634 million and 10,000 or less needs to show how U/Pb dating can be so wrong, while radioactive decay rates, which depend on the weak nuclear force, still allowed for the formation of atoms and so life itself when the magic creator supposedly created it.
At least two global “Snowball Earth” glaciations occurred during the Neoproterozoic Era (1000-538.8 million years ago). Post-glacial surface environments during this time are recorded in cap carbonates: layers of limestone or dolostone that directly overlie glacial deposits. Postulated environmental conditions that created the cap carbonates lack consensus largely because single hypotheses fail to explain the cap carbonates’ global mass, depositional timescales, and geochemistry of parent waters. Here, we present a global geologic carbon cycle model before, during, and after the second glaciation (i.e. the Marinoan) that explains cap carbonate characteristics. We find a three-stage process for cap carbonate formation: (1) low-temperature seafloor weathering during glaciation generates deep-sea alkalinity; (2) vigorous post-glacial continental weathering supplies alkalinity to a carbonate-saturated freshwater layer, rapidly precipitating cap carbonates; (3) mixing of post-glacial meltwater with deep-sea alkalinity prolongs cap carbonate deposition. We suggest how future geochemical data and modeling refinements could further assess our hypothesis.
Introduction
Earth’s Neoproterozoic Era (1 billion years ago to 538.8 million years ago) is marked by dramatic global climate change. Geologic evidence indicates two major glacial intervals where ice sheets reached low latitudes for millions of years (e.g., reviewed by Hoffman et al.1). These “snowball Earth” events2,3 are the Sturtian from 717 to 659 million years ago (Ma) and the Marinoan from ca 645 to 635 Ma. Together, these events bookend the Cryogenian Period (720–635 Ma).
The Cryogenian glacial intervals occurred alongside other global changes, including the appearance of the first large, complex organisms in Earth’s history in the subsequent Ediacaran Period4, an increase of atmospheric O2 relative to low levels in the mid-Proterozoic5, large excursions in the global carbon isotope record6, and the break-up of Rodinia and later assembly of Gondwana supercontinents7. All of these transitions occurred during or continued after the Cryogenian Period, which is only ~2% of Earth’s 4.5-billion year history. Despite this temporal connection, the causes and the relationships between these global changes remain unclear.
Cap carbonates (CCs) probe Earth’s surface environment during, and immediately after, the Cryogenian. CCs are layers of limestone or dolostone up to ~200 meters thick that sharply overlie Sturtian and Marinoan glacial deposits in over 50 locations on all major Neoproterozoic continents (reviewed by Yu et al. 8). Carbonates record Earth’s surface conditions because they are sensitive to the chemistry of the atmosphere and ocean from which they precipitate. Thus, the sharp distinction between the glacial deposits and CCs is interpreted as an abrupt shift in Earth’s surface environment at the end of each Cryogenian glacial interval from cold, frozen conditions to hot conditions with a high partial pressure of atmospheric carbon dioxide, pCO23. In this scenario, continental weathering was inhibited during the glacial intervals, allowing volcanic CO2 to accumulate in the atmosphere and provide enough greenhouse warming to overcome the high albedo of Earth’s ice-covered surface, causing deglaciation. The post-glacial Earth then entered a high pCO2 but low albedo state in which continental weathering produced cations and carbonate ions (i.e. alkalinity) that drove rapid carbonate deposition2,3.
The above explanation for CC deposition is broadly consistent with the geologic evidence, but a complete explanation must answer several key questions. First, was the alkalinity source from continental weathering sufficient for the CCs? It is estimated that the global mass of the Marinoan CCs is over 1018 kg8. Enough alkalinity to generate this much carbonate must be supplied after the glacial interval. Second, what was the timescale of CC deposition? The interpretation of sedimentary structures, the presence of paleomagnetic reversals, and radiometric dating yield conflicting estimates that have yet to be resolved (Table 1). Third, what were the physical and chemical properties of the water body from which the CCs precipitated? After the Marinoan glaciation, the post-glacial ocean was subject to a large influx of glacial meltwater, sea level rise, and transgression onto the land. The deposition of the CCs was likely influenced by these changing ocean conditions.
Many explanations for CC deposition have been proposed, but none are complete. As summarized in Yu et al.8, suggestions include oceanic overturn9,10, continental weathering1,11, gas hydrate destabilization12,13, glacial meltwater plumes and subsequent ocean overturn14, sediment starvation15,16, microbial activity17,18, and calcareous loess19. Also summarized in Yu et al.8, these explanations all have unresolved deficiencies related to the physical and chemical conditions of the post-glacial ocean, the interpretation of the geologic evidence, and the predicted timescale of deposition.
Advances in our knowledge of the geologic carbon cycle and of Cryogenian conditions allow new tests of hypotheses for CC deposition.
Seafloor weathering has been recognized as a process in the geologic carbon cycle that has been important during some times in Earth’s history. Seafloor weathering occurs when seawater circulating through oceanic crust at low-temperatures reacts with constituents of basaltic rock (e.g., volcanic glass, olivine, and plagioclase) to release alkalinity in the form of Ca ions (e.g. reviewed by Coogan and Gillis20). Krissansen-Totton and Catling21 developed an empirically justified parameterization of seafloor weathering in a geologic carbon cycle model, and Krissansen-Totton et al.22 used this model to show that seafloor weathering may have been comparable in strength to continental weathering at some points in Earth’s history. The role of seafloor weathering in CC deposition has not been assessed. Previous global geologic carbon cycle models applied to Cryogenian glacial intervals used theoretical rate parameterizations that have proven inconsistent with recent experiments23, or they omit low-temperature seafloor weathering24,25,26.
The Marinoan CCs were likely deposited in a stratified, post-glacial ocean. The large volume of glacial meltwater following deglaciation should have created a distinct layer on top of the existing ocean. It has been proposed that the dolostone components of the CCs precipitated out of this layer14. This hypothesis is supported by geochemical measurements of the CCs, including 87Sr/86Sr and δ26Mg in multiple formations27,28,29 and a global analysis of Ca, Mg, Sr, and C isotopes30. A freshwater layer is consistent with 1D and 3D ocean models, which show that it could last for up to 105 years31,32. Thus, the evidence indicates that the meltwater layer must be considered in CC deposition; however, the previous global geologic carbon cycle models only consider whole-ocean chemistry.
Here, we investigate CC deposition with a geologic carbon cycle model that includes an empirically justified parameterization of seafloor weathering, explicit calculation of chemistry in the post-glacial meltwater layer, and other advances in our knowledge of both the geologic carbon cycle and Cryogenian conditions. Our model is applied to the Marinoan glaciation, but many aspects are likely applicable to the Sturtian and perhaps other glaciations. We identify a mechanism for Marinoan CC deposition that builds on previous explanations to answer the key questions mentioned above, and we find it is consistent with the global collection of CCs (See Supplementary Fig. S1).
Otherwise, you are stuck with the unarguable evidence that the Bible's authors got is all spectacularly wrong by many orders of magnitude, so could not possibly have been written by an omniscient creator god.
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