ERTH 11

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What is snowball earth

Snowball Earth refers to a hypothesis that suggests the Earth was entirely or nearly entirely frozen at least once during the Cryogenian period, which lasted from about 720 to 635 million years ago. This extreme glaciation is believed to have been caused by a combination of factors, including a decrease in atmospheric carbon dioxide levels and changes in solar output.

Snowball Earth refers to an extremely stable climate state where

the Earth’s surface is covered from poles to equator in ice. (Pan glacial state)

• This climate state is also termed a pan-glacial state.

this snowball earth is so stable because it is at a radiative balance

The sun was slightly brighter at this age which means that the CO2 levels must have been higher to maintain the necessary greenhouse effect to prevent complete glaciation. When the glaviation bgan the albedo INCREASED which would have cased the earth to glaciate faster as more sunlight was reflected back into space, further lowering global temperatures and accelerating the cycle of glaciation.

A little history /a timeline of events

There is a considerbale evidince for and extenisive glaciation some 600 million years ago. t caued an alteraion of limate that made possible the proliferation of animal life in the cabrian times

We find glaicial deposits where there is no glaiver anywhere near

In the cabrian era there was a HUGE explosion of life, then there was a large gap in thr rock record whre the eveidince of life was halted with is evidince that life was not moble I.E not moving/ frozen for an extended period, possibly due to extreme environmental conditions such as glaciation or anoxia, which limited the diversity and distribution of species.

What does this mean?

• What age are these different glacial deposits and how do we know they are glacial?

• Are they all the same age or is it a broad interval where ice has been periodically been on the planet at different elevations and locations?

The Sturtian Glaciation

• Named after the Sturt formation in Southern Australia which is named after the Sturt Gorge, which was named after the Sturt river which was named after Charles Sturt in 1831 by Collet Baker.

• The Sturtian Glaciation is dated to have occurred between 717 and 659 Million years ago.

• This means it’s total duration was ≈56 Million years

The Marinoan Glaciation

• Named after the Marino Suburb of Adelaide in Southern Australia

• The Marinoan Glaciation is dated to have initiated between 654 and 639 Million years ago and ended at 635 Million years ago.

• This means it’s total duration was ≈19-4 Million years with most recent estimates favouring a 4 million year duration

Most recent studies suggest only 4myrs

When we enter glaciation we beign t oprecititae mass ammount of water, on to land, which can lead to significant changes in sea levels and climate patterns, which leads to coast lines moving seawards, which will expost the rock records aroudn the coast and will lead to mass weathering and eraseing the rock records

A fold test, is a test used to determine the orientation and geometry of folds in geological formations, providing insights into the tectonic history and stress conditions that shaped the Earth's crust during that period. if all the magnetic stripes are aligned in the same direction, it indicates a period of normal magnetic polarity, while a reversal in their orientation suggests episodes of geomagnetic reversals that have occurred throughout Earth's history.

glacial deposits in Northwest canada and Namibia provide evidence of a glacer depositing sediment in both areas.

evidence of snowball earth

A return of iron formations is evince of dexogination

Recall, oxygenated oceans do not carry much dissolved iron

• However in waters with no oxygen, waters can hold lots of iron

• This is a prerequisite to form iron formations

• But if we had oxygen in the atmosphere how would these form?

The reappearance of Fe-formations suggest a return to largely anoxic oceans

• This is consistent with the atmosphere being cut off from the ocean

meaning that the atmosphere is going to loose contnat with the oceasn menaing that the ocean will be DEOXYGENATED

life in a snowball

What about life when the ocean is deoxygenated?

• it dies

Maybe there was cracks in the ice with allows for O2, these large cracks would cause for a massive shift in the life spread over the world.

Cryoconite:

The dark cryocantite would attract large ammounts of sunlight and aybe life could live in the meltwater

Hydrothermal vents

: These underwater geothermal features can provide essential nutrients and heat, creating unique ecosystems that support diverse marine life, even in the absence of sunlight.

Hydrotherms maybe evolved ???

Life after the snowball earth

Life BLOOMED(it shocked the muscle basicly)

exiting a snowball

How?

Carbonate sequences

Volcanes case MASSIVE greenhouse affects with CO2 and superheat the earth , leading to rapid melting of ice and increased sea levels.

Cap carbonates

• Cap carbonates are thick sequences of post glacial carbonates

• The sequence of glacial diamictite overlain by carbonate units is found all around the Earth

• This is important because:

a) carbonates form in warm shallow waters and

b) all of that CO2 that built up needed to go somewhere

• To get all of the Ca we must have had extreme weathering rates

outstanding controversies

• Why were there two?

• Why are their durations so different?

• How did they initiate? Did they have the same causal mechanism?

• How did life survive under the ice? And what is the relationship to Snowball Earth and evolution afterward?

• Did oxygen rise in the atmosphere or fall in the atmosphere during these events?

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Climate Engineering Strategies

• Reflective cooling methods are being explored as climate engineering strategies.

• One proposed method involves simulating the effects of nuclear winter, possibly in response to asteroid impacts.

Albedo Concept

• Albedo measures the reflectivity of surfaces, with ice having a high albedo value approaching 1.

• The current Earth’s average albedo is approximately 0.3.

• Changing the albedo significantly impacts Earth's temperature, making it a critical factor in climate science.

  • For instance, a higher albedo means more sunlight is reflected away from the Earth’s surface.

  • If too much reflection occurs (albedo of 1), it could result in extremely low temperatures, akin to a frozen Earth.

  • Conversely, a lower albedo (like 0.3) reflects less sunlight, contributing to warmer climatic conditions.

Historical Context of Snowball Earth

• Investigation into glacial deposits dates back to the 1960s, revealing insights into past climates.

• Initially, strange glacial deposits in warmer regions were often attributed to myths rather than scientific explanations.

• The geologist Harlan, in the 1890s, studied ancient glacial deposits by analyzing glacial diamictites and their associated striations, indicating past glacial activity.

• Striations were formed by rocks carried underneath glaciers scratching the bedrock.

Glacial Deposits and Age

• Evidence for glacial deposits dates back older than the Cambrian period, suggesting multiple glacial events across millions of years.

• The observation and classification of ancient glaciers continued to evolve through advancements in geology and paleontology.

• Glacial deposits found in various locations suggest distinct glacial periods, challenging assumptions about their simultaneous occurrence.

Timeline of Glaciations

• A detailed timeline depicts various ice ages over the past 3 billion years, with key periods such as the Sternian and Marinoan glaciations.

• The Sternian glaciation lasted longer than the Marinoan, indicating its global impact.

• The Marinoan glaciation dates around 640-635 million years ago and was characterized by significant geological and biological changes.

Evidence from Fossil Records

• The fossil record provides insight into Earth's biota transitions across major glacial periods.

• Following the glacial periods, life flourished, marking significant evolutionary milestones after periods of extreme climatic stress.

Causes and Consequences of Glaciation

• Glaciations deeply impacted sea levels, coastlines, and the availability of sediments for geological records.

• Ice cover can lead to a seaward movement of coastlines and weathering of land previously submerged.

• Severe drops in sea levels during glaciations reveal much about the climatic conditions of those times.

Paleomagnetism and Geochronology

• Paleomagnetism helps reconstruct ancient continental positions and orientations by studying magnetic minerals in rocks.

• Geochronology using isotopes like uranium and lead allows for precise dating of glacial deposits, improving understanding of the timeline of climatic events.

• Discrepancies found in rock formations may provide evidence for the timing and location of glaciations spanning millions of years.

Significance of Cap Carbonates

• After glacial periods, cap carbonates are formed under rapidly changing climate conditions, indicating a shift to warmer environments.

• These deposits suggest that after a glacial event, carbonates typically form in shallow, warm tropical waters.

• The significant accumulation of CO2 from volcanic activity leads to greenhouse conditions necessary to melt extensive ice sheets and initiate rapid changes in climate.

Biological Impacts of Glaciation

• The harsh conditions of Snowball Earth likely forced life forms into limited viable habitats, possibly aiding in rapid evolutionary changes post-glaciation.

• Speculation exists connecting glaciation events with bursts of biodiversity, particularly as climates stabilize after intense periods of change.

• The study of Snowball Earth emphasizes the connection between extreme climate events and significant evolutionary innovations.