Neoproterozoic Earth History

Choose a study mode

Play Quiz
Study Flashcards
Spaced Repetition
Chat to Lesson

Podcast

Play an AI-generated podcast conversation about this lesson
Download our mobile app to listen on the go
Get App

Questions and Answers

Explain how the breakup of the supercontinent Rodinia contributed to the conditions leading to the Neoproterozoic Snowball Earth events.

The breakup of Rodinia led to extensive volcanic activity near the equator. The weathering of the resulting igneous rocks consumed atmospheric CO2, reducing the greenhouse effect and cooling the planet.

Describe the role of ice-albedo feedback in the intensification of the Neoproterozoic Snowball Earth glaciations.

As ice cover expanded due to cooling, the Earth's albedo increased, reflecting more solar radiation back into space. This further reduced global temperatures, leading to more ice formation and a positive feedback loop that intensified the glacial conditions.

What geochemical evidence supports the idea that the Neoproterozoic oceans were highly alkaline during cap carbonate formation?

The presence of thick cap carbonates, composed of carbonate minerals, indicates a rapid influx of alkaline ions (e.g., Ca2+) into the ocean after the glacial periods, resulting in widespread carbonate precipitation.

Discuss the challenges in reconciling the Snowball Earth hypothesis with the survival and diversification of life during the Neoproterozoic.

<p>A completely frozen Earth would have posed extreme challenges for life's survival. Possible refuges included ice-free regions near volcanic vents, areas of thin ice allowing photosynthesis, or chemosynthetic ecosystems.</p>
Signup and view all the answers

Describe the evidence from sedimentary rocks, such as diamictites and dropstones, that supports the occurrence of widespread glaciation during the Neoproterozoic.

<p>Diamictites are poorly sorted sedimentary rocks containing a wide range of clast sizes, indicative of glacial till. Dropstones are isolated clasts found in fine-grained sediments, deposited by melting icebergs or ice sheets.</p>
Signup and view all the answers

Explain why carbon isotope ratios tend to be low in sedimentary rocks deposited during Neoproterozoic glacial periods.

<p>Glacial periods are associated with reduced biological productivity due to ice cover. This leads to a decrease in the removal of the lighter carbon isotope (C) from the ocean, resulting in lower C/C ratios in the resulting sedimentary rocks.</p>
Signup and view all the answers

What are cap carbonates, and what environmental conditions are believed to have led to their formation immediately following Neoproterozoic glacial periods?

<p>Cap carbonates are thick sequences of carbonate rocks that overlay glacial deposits. They are thought to have formed due to rapid weathering of the land surface and increased alkalinity in the ocean from high greenhouse gas concentrations after the glacial period, combined with high levels of dissolved calcium in the ocean from hydrothermal activity.</p>
Signup and view all the answers

How does the "slushball Earth" hypothesis differ from the "snowball Earth" hypothesis, and what evidence is cited to support the slushball Earth scenario?

<p>The slushball Earth hypothesis posits that not all of Earth was completely frozen, leaving some open water at the equator and/or thin ice cover. Proponents cite evidence like presence of banded iron formations (BIFs); biological activity being impossible in &quot;Snowball Earth&quot;</p>
Signup and view all the answers

Besides the 'snowball Earth' and 'slushball Earth' hypotheses, what is the 'zipper-rift Earth' hypothesis?

<p>The zipper-rift Earth hypothesis suggests that rifting caused local highs, and, as such, discontinuous localised glaciations.</p>
Signup and view all the answers

How did the evolution of skeletonization in the late Ediacaran and Cambrian periods lead to new evolutionary pressures?

<p>The development of mineralized skeletons and hard parts in organisms led to increased opportunities for predation, encouraging the evolution of more robust defenses or more efficient hunting strategies and leading to what is sometimes called an 'evolutionary arms race'.</p>
Signup and view all the answers

Discuss the role of 24-isopropyl cholestane in understanding early animal evolution during the Neoproterozoic.

<p>24-isopropyl cholestane is a steroid biomarker found in Neoproterozoic sediments, specifically associated with sponges. The presence and abundance of this biomarker suggests that sponges, a type of animal, may have existed earlier than the first animal fossil dates.</p>
Signup and view all the answers

Describe the significance of the Ediacara Hills in Australia and Charnwood Forest in the UK to our understanding of Precambrian life.

<p>The Ediacara Hills and Charnwood Forest contain some of the oldest known fossil assemblages of multicellular organisms. They show a community of soft-bodied organisms that look different to anything alive today.</p>
Signup and view all the answers

Why does the fossil record of body fossils expand much more in sediments of the Ediacaran age, versus using molecular data?

<p>Molecular dating is inexact because mutation rates are variable. As such, the fossil record is the best tool to determine the age for a fossil of interest.</p>
Signup and view all the answers

What are the primary differences between the Sturtian and Marinoan glaciations, and how are these differences reflected in the geological record?

<p>The Sturtian glaciation occurred earlier and was marked by more severe and prolonged ice cover, while the Marinoan glaciation was shorter but still extensive. The geological record shows differences in the thickness and distribution of glacial deposits, as well as variations in post-glacial cap carbonate sequences.</p>
Signup and view all the answers

What evidence suggests that high seasonality at equatorial paleolatitudes may have characterized the 'high-tilt Earth' hypothesis?

<p>In the high-tilt Earth hypothesis, the high seasonal effects would have influenced the types of sediments deposited at different latitudes, changing the rock types deposited. More evidence is needed to test if this is true.</p>
Signup and view all the answers

What are the characteristics of the fossils of Ediacaran age?

<p>Ediacaran fossils have a variety of forms and shapes that are hard to relate to organisms with modern representatives.</p>
Signup and view all the answers

During the Neoproterozoic era, what process likely aided the biomineralisation of marine organisms?

<p>Marine environments are characterised by abundant Ca and P, allowing the mineralisation of carbonate and phosphate hard parts.</p>
Signup and view all the answers

What characterises the period of Earth history referred to as the 'boring billion'?

<p>The 'boring billion' is characterised as having less tectonic action and less erosion. As such, there is less carbon dioxide to weather.</p>
Signup and view all the answers

When were the Ediacaran fossils of Charnwood Forest in the UK discovered?

<p>They were discovered in the 1950s.</p>
Signup and view all the answers

Give an example of a location in Scotland with rock that shows evidence of conditions in the Neoproterozoic era, back to the 1870s.

<p>Islay, Scotland</p>
Signup and view all the answers

How did continuous gas emissions due to volcanic activity lead to glacier melting, according to "A model to explain Snowball Earth"?

<p>It leads to increasing the greenhouse effect, trapping more heat at the Earth's surface.</p>
Signup and view all the answers

According to the reference diagram showing locations associated with the Marinoan glaciation, which is closer to the South Pole: Namibia (N.Nam) or South Australia (S. Aus)?

<p>South Australia (S. Aus)</p>
Signup and view all the answers

Describe the two main categories of evidence scientists use to assess the 'snowball Earth' theory.

<p>The two main categories are glacial features and cap carbonates.</p>
Signup and view all the answers

Under the Snowball Earth hypothesis, could life have survived solely in areas of localized, low latitude glaciation?

<p>No, not according to the Snowball Earth Theory. Other theories, such as the zipper-rift Earth theory or the high tilt Earth, might.</p>
Signup and view all the answers

Under the Snowball Earth theory, what is the minimum amount of time necessary for prolonged glaciations to occur?

<p>Millions of years.</p>
Signup and view all the answers

Where are the Shetland Islands located?

<p>The Shetland Islands are located to the northeast of Scotland.</p>
Signup and view all the answers

What is the hypothesized trigger for runaway ice-house conditions?

<p>It occurs when partial pressure of carbon dioxide, or PCO2, eventually crosses a threshold.</p>
Signup and view all the answers

On the chart related to Ice line latitude as a function of PCO2, what axis is on the X axis?

<p>The X axis is labelled &quot;PCO2 (wrt present)&quot;.</p>
Signup and view all the answers

What does 'wrt' mean on the chart that measures 'Solar flux (wrt present)'?

<p>With respect to.</p>
Signup and view all the answers

How much higher was the Age (10^6 years before preent) in Ediacaran versus Cryogenian?

<p>Ediacaran was about 540 to 630 millions of years, whereas Cryogenian was about 630 to 720 on the provided timeline.</p>
Signup and view all the answers

Flashcards

Snowball Earth

A period of extreme glaciation in Earth's history during the Neoproterozoic era.

Diamictite

Sedimentary rocks containing poorly sorted clasts in a matrix, often associated with glacial deposits.

Cap Carbonates

Rocks formed from the precipitation of carbonate minerals, frequently found overlying glacial deposits from the Snowball Earth.

Rodinia

Supercontinent that existed during the Neoproterozoic era.

Signup and view all the flashcards

Ediacaran Period

A period in the Neoproterozoic era associated with a significant diversification of multicellular life.

Signup and view all the flashcards

Cambrian Explosion

The relatively sudden appearance of diverse animal forms in the fossil record during the Cambrian period.

Signup and view all the flashcards

Biomineralization

The process by which living organisms produce minerals, leading to the formation of shells and skeletons.

Signup and view all the flashcards

Snowball Earth

Climate state with necessary prolonged glaciations, and severe glaciations with high CO2 atmosphere

Signup and view all the flashcards

Slushball Earth

Climate state analogue that has modern sedimentological analogues for facies

Signup and view all the flashcards

Zipper-rift Earth

Climate state analagoue that has regional controls on glaciation and continental rifting

Signup and view all the flashcards

Study Notes

  • The lecture focuses on Neoproterozoic Earth history, Snowball Earth and alternatives, Ediacaran Faunas, and the Proterozoic-Phanerozoic transition, covering a period from 0.8 to 0.54 Ga.

Distribution of Neoproterozoic rocks in the UK

  • Neoproterozoic rocks appear in Wales, England, and Northern Ireland and Scotland
  • The largest exposures are in Scotland, known as the "Dalradian Supergroup"
  • Grampian is the oldest and South Highland Group is the youngest group
  • Charnwood Forest, near Leicester, England is also an important outcrop

Sedimentary features of the Neoproterozoic

  • Descriptions of rocks showing extreme geological conditions date back to the 1870's
  • Diamictite provides evidence of glacial conditions
  • Thick sequences of carbonates overlie diamictites
  • Glacial marine tills are found in the Ghaub Formation, Namibia
  • Drifting icebergs calved from marine terminating glaciers supply clasts to the marine sediments when they melt.

Model of diamicton deposition

  • Clasts in marine sediments are supplied by drifting icebergs calving from marine terminating glaciers

Observed sedimentary strata

  • Idealized sequences of sediments found in Islay have been drawn

Marinoan vs Sturtian deposits

  • Diamictites lie on top of an erosional surface
  • Diamictites are followed by thick sequences of carbonates
  • Initial sedimentary structures are indicative of deepening and relatively deep water later shallowing upwards

Palaeogeography of the Cryogenian

  • Glacial deposits occurred during two episodes, indicating the presence of a supercontinent.
  • "Rodinia" is thought to have broken up during the Cryogenian
  • Breakup of Rodinia resulted in emplacement of large quantities of igneous rocks near the equator, easily weathered

Records of isotopic proxies over the Neoproterozoic interval

  • Carbon isotope ratios are low near glacial deposits
  • Carbon isotope ratios tend to be very high before and between such intervals, similar to the Lomagundi Event
  • 87Sr/86Sr ratios increased over the last 250 million years of the Neoproterozoic, signalling Sr from continental weathering

Snowball Earth hypothesis

  • Radiometric dating and other correlation techniques confirm two glaciation periods in the Cryogenian Period
  • Glacial features and 'cap carbonates' are found across continents, except Antarctica
  • Glaciation extended to tropical latitudes as palaeogeographic reconstructions suggest

Theory of prolonged Snowball Earth

  • A viable mechanism must explain the long duration of Snowball Earth events
  • Reduction in CO2 leads to increased glaciation.
  • Eventually crosses threshold for runaway ice-house, leading to equatorial ice and low planetary temperature
  • Volcanic activity gradually increases PCO2 for millions of years
  • Increased PCO2 crosses threshold which quickly increases the temperature and sea level
  • Weathering and carbonate formation take up excess CO2

Cap carbonates

  • Cap carbonates occur after glaciations in geological strata
  • Explained by mixing an alkaline ocean and CO2 rich atmosphere, forming carbonates
  • Enormous in size, consistent with a large amount of CO2

Snowball Earth Criticism

  • How could life survive millions of years of continuous glaciation?

Zipper-rift Earth theory

  • Rifting caused local highs and discontinuous localized glaciations

High Tilit Earth theory

  • Earth's rotation axis was tilted more
  • Low latitude seasonality might have been high
  • Local glaciation may have occurred

Slushball Earth theory

  • Not all the Earth was glaciated, allowing refuge for life

"Multipole" Earth theory

  • Palaeogeographic reconstructions could be inaccurate
  • Different character of Earth's magnetic field

Ediacaran evolution and faunas

  • Molecular clock estimates indicate life diversified during the Cryogenian and Ediacaran.
  • Body fossils, rather than molecular and geochemical evidence, are expanded in Ediacaran sediments
  • Significant finds were made in the 1940s in the Ediacara Hills, Australia, and the 1950’s in Charnwood Forest, UK

Ediacaran fossils

  • Typical specimens are soft-bodied
  • Some could become larger than 1 meter
  • They have a variety of shapes that are hard to relate to organisms with modern representatives
  • Habitats, modes of life and evolutionary trends are still poorly understood

Shelly Fauna and Cambrian explosion

  • Organisms with mineralised hard parts have been found in sedimentary strata as old as the late Ediacaran
  • Biomineralisation and appearance of organisms mark the transition of Phanerozoic
  • Biomineralisation aided by marine environments with abundant Ca and P, allowing mineralization of carbonate and phosphate

Cambrian explosion and evolutionary arms race

  • Protective shells and mineralised appendages led to biodiversity from predation
  • Organisms building more sophisticated protection countered more efficient predation
  • Biodiversity aided by oxygen availability
  • Animals expanded into wider habitat

Studying That Suits You

Use AI to generate personalized quizzes and flashcards to suit your learning preferences.

Quiz Team

Related Documents

Use Quizgecko on...
Open
Browser
Browser