前寒武紀（Precambrian）是地史學中對在顯生宙寒武紀之前的地球地質歷史的非正式統稱，原本的名稱是隱生宙或隱生元（Cryptozoic），但後來拆分成冥古宙、太古宙與元古宙三個大的地質年代。前寒武紀開始於大約46億年前地球形成，結束於約5億4200萬年前開始大量出現生物實體化石的寒武紀早期。
# 寒武紀之前的地質年代是「元古宙」（Proterozoic Eon），距今24億年前至5.41億年前。
埃迪卡拉紀（Ediacaran），又稱艾迪卡拉紀[3]、震旦紀（Sinian）、文德紀（Vendian），是元古宙最後的一段時期，其後緊接著便是顯生宙的開端──古生代的寒武紀。埃迪卡拉紀一般指6.35-5.41億年前。
# 埃迪卡拉生物群（Ediacaran biota）是1946年發現於南澳洲埃迪卡拉山的末遠古系龐德石英岩中的化石群，這類化石群已在世界30多個地點被發現。它們是迄今已知最早的複雜多細胞生物。[5][6]
埃迪卡拉動物和今天的大多數動物截然不同，牠們既沒頭、尾、四肢，也無口部和消化器官，因此牠們大概只能從水中攝取養份。大多的埃迪卡拉動物固著在海底，和植物十分相近，其他的則平躺在淺海處，等待營養順水流而送上門來。埃迪卡拉動物化石出土越多，反而越沒有規律。有一些化石比較像後來動物的先驅。
在埃迪卡拉紀末期，埃迪卡拉動物分成兩支，牠們有的成功演化成更有活力，更具進攻性的動物，並在之後的寒武紀大爆發中大放異彩，成為現今大多數動物門的祖先。而有的則走向滅亡，牠們的特徵也永遠消失於歷史舞台上。
# 埃迪卡拉紀末期滅絕事件（End-Ediacaran extinction）又稱震旦紀末期滅絕事件，是一次可能發生在約5.42億年前埃迪卡拉紀末期的大滅絕。該次事件包括疑源類生物的大型集體滅絕、埃迪卡拉生物群突然消失以及寒武紀大爆發之前的一段地球生命空白期。
前埃迪卡拉紀生物
在埃迪卡拉紀（又被稱作震旦紀）的地層，有兩種主要的化石種類：一種是稱作埃迪卡拉生物群的軟體生物，其化石被微生物殘骸所形成的軟墊保存了下來；另一種則是鈣化生物（英語：calcifying organisms），例如具有碳酸鈣骨架的克勞德管蟲以及納馬籃蟲[1]。由於這兩種生物群同時突然在埃迪卡拉紀末期（約5.42億年前）消失，他們的滅絕無法簡單以原先所猜測的[1]埃迪卡拉型保存層的關閉來解釋[2]。
後埃迪卡拉紀生物
在寒武紀早期（埃迪卡拉紀剛結束）的化石紀錄中，出現了生物鑽洞的活動量與型態多樣性同時突然的增加的現象（寒武紀底質革命）。然而，寒武紀大爆發所導致的化石增加並沒有隨即發生。這表示寒武紀大爆發並不是取代原先的生物群而使其滅絕。反之，與現有資料比較相符的解釋是因為生態區位的空出，使後來輻射演化出的各種生物能順利地填入相符的區位[3]。
如果在後埃迪卡拉紀時期發現任何埃迪卡拉生物，就表示牠們並非都在寒武紀開始時就絕滅了。有些屬於下寒武紀的生物，如奇翼蟲，一度被認為屬於埃迪卡拉生物群，但這個假說如今已不再盛行[4]。另一個可能的埃迪卡拉倖存者是Ediacaria，因為在上寒武紀地層中有發現疑似是其固著器的結構，但科學界尚未有共識。如果這真的是埃迪卡拉生物所留下的遺跡，表示其並未在本次大滅絕中完全消失。然而，反對此說者認為，這些化石實際上並不具有生物性的起源，但越來越多證據表明它應該是一個有機體（或至少是起源於生物，例如微生物菌落）[a]，只是與埃迪卡拉生物群無關[5]。
倖存的生物種類
顯然，有部分生物存活過了這次大滅絕，因此地球上的生命才得以存續至今。然而，只有極少部分的生物種類在埃迪卡拉紀-寒武紀交界帶兩側被同時發現。其中一種是凝集的有孔蟲門生物Platysolenites[6]。其他明顯的倖存者，例如奇翼蟲，被重新解釋為與埃迪卡拉生物群無關。
# 雪球地球（Snowball Earth）也稱冰室地球（Icehouse Earth），是地史學上為了解釋一些史前地質現象而提出的假說，認為在地球地質歷史上曾經出現過冰雪覆蓋所有地表（陸地和海洋）的冰河期。此詞通常專指成冰紀大冰期（Cryogenian Ice Age），即元古宙新元古代成冰紀發生過至少一次嚴重的全球性冰期，以至於地球上的陸地和海洋全部被凍結，僅僅在厚達兩公里的冰層下存有少量因地熱活動而融化的液態水。
Is there evidence of snowball earth? (ChatGPT, 2024-6-27)
Yes, there is substantial evidence supporting the Snowball Earth hypothesis, which suggests that the Earth experienced one or more periods of global-scale glaciation, where ice covered much or all of the planet's surface. Here are some key pieces of evidence:
1. **Glacial Deposits**: Geological formations known as "tillites" or "diamictites," which are composed of unsorted glacial debris, have been found in tropical and equatorial regions. This suggests that glaciers once existed at low latitudes, which would be consistent with a global glaciation event.
2. **Cap Carbonates**: Directly above the glacial deposits, there are layers of carbonate rock known as "cap carbonates." These are believed to have formed rapidly as the Earth transitioned from a frozen state to a warmer climate, causing a significant increase in weathering and deposition of carbonates.
3. **Paleomagnetic Evidence**: Studies of the Earth's ancient magnetic field (paleomagnetism) indicate that glacial deposits were indeed formed near the equator. The magnetic minerals in these rocks point to their original formation at low latitudes.
4. **Banded Iron Formations (BIFs)**: There are occurrences of banded iron formations around the time of the supposed Snowball Earth events. These formations are believed to have been produced in an ocean that was cut off from the atmosphere, leading to iron deposition once the ice began to melt and oxygen levels increased.
5. **Isotopic Signatures**: Isotopic analysis of carbon and oxygen in ancient rocks shows unusual variations that are consistent with a global glaciation and subsequent deglaciation. For instance, the carbon isotope ratios show large swings that could be attributed to changes in global organic carbon burial and oxidation.
6. **Climate Models**: Computer models of Earth's climate also support the possibility of a Snowball Earth. These models show that once ice sheets advance beyond a certain point, the Earth's albedo (reflectivity) increases, leading to a runaway cooling effect that could result in global ice coverage.
The primary Snowball Earth events are thought to have occurred during the Cryogenian period, particularly during the Sturtian (approximately 717 to 660 million years ago) and Marinoan (approximately 640 to 635 million years ago) glaciations. These periods are still subjects of active research and debate within the scientific community.
埃迪卡拉生物群（英語：Ediacaran biota）又稱艾迪卡拉生物群[1]，是一群神秘的盤狀、管狀、葉狀或袋狀形態的前寒武紀生物，生活在元古宙末期的埃迪卡拉紀（5億8000萬年前~5億4200萬年前）。埃迪卡拉生物群是迄今已知最早的大規模多樣化並出現特化解剖結構的多細胞生物群體[註 1]，因其模鑄化石和遺蹟化石1946年在南澳大利亞弗林德斯山脈以西的埃迪卡拉山石英岩中首次發現而得名。同類遺蹟化石已在世界30多個地點被發現，因為另一處著名的化石群為處於加拿大紐芬蘭島東南角的阿瓦隆半島，因此埃迪卡拉生物群的演化輻射事件也稱阿瓦隆大爆發（Avalon Explosion）。
What caused the Ediacaran biota extinction? (ChatGPT, 2024-6-27)
The extinction of the Ediacaran biota, which occurred around 541 million years ago, is a subject of ongoing research and debate among scientists. Several hypotheses have been proposed to explain this event, and it is likely that a combination of factors contributed to the extinction. Here are some of the main hypotheses:
1. **Environmental Changes**: Significant changes in the Earth's environment could have played a critical role. This includes changes in ocean chemistry, such as shifts in oxygen levels, which would have affected the availability of habitable niches for the Ediacaran organisms.
2. **Climate Changes**: The transition from the Ediacaran to the Cambrian period was marked by climatic shifts that could have impacted the biota. Cooling or warming events might have altered habitats and ecosystems in ways that the Ediacaran organisms could not adapt to.
3. **Predation**: The rise of new predators during the Cambrian period could have contributed to the extinction of the Ediacaran biota. The development of more complex feeding behaviors and new predators could have created pressures that the relatively simple Ediacaran organisms could not withstand.
4. **Evolutionary Competition**: The advent of the Cambrian explosion brought about a rapid diversification of life forms, including many with hard parts and more complex body plans. This increase in biodiversity and the development of new ecological niches may have outcompeted the Ediacaran organisms for resources and space.
5. **Changes in Ocean Chemistry**: There is evidence suggesting that changes in oceanic nutrient levels and chemical composition could have disrupted the ecosystems in which the Ediacaran biota thrived. For example, changes in nutrient availability could have impacted the base of the food chain, leading to a cascade of extinctions.
6. **Tectonic Activity**: Geological activity, such as the movement of tectonic plates, could have caused changes in sea levels, the formation of new landmasses, and the alteration of ocean currents. These changes might have led to habitat destruction or the creation of barriers that isolated populations and disrupted ecosystems.
Each of these factors, alone or in combination, could have contributed to the decline and eventual extinction of the Ediacaran biota. The exact causes remain a topic of scientific inquiry, and ongoing research continues to shed light on this critical period in Earth's history.
寒武紀大爆發（亦稱寒武紀生命大爆發，Cambrian Explosion），是相對短時期的演化事件，開始於距今5.41億年前的寒武紀時期，化石記錄顯示絕大多數的動物「門」都在這一時期出現了[1][2]。它持續了2千萬年[3][4]-2.5千萬年[5][6]，它導致了大多數現代動物門的發散。 因出現大量的較高等生物以及物種多樣性，於是，這一情形被形象地稱為生命大爆發。這也是顯生宙的開始。在世界各地發現的化石群共同印證了這一生命演化史上的壯觀景象。
How does Darwin’s theory of evolution explain the process from the end-Ediacaren extinction to the Cambrian explosion? (ChatGPT, 2024-6-27)
Darwin’s theory of evolution by natural selection provides a framework to understand the transition from the end-Ediacaran extinction to the Cambrian explosion. Here’s how it applies to this critical period in the history of life:
### 1. Natural Selection and Adaptation
- **Post-Extinction Opportunities**: After the end-Ediacaran extinction, many ecological niches were left vacant. Natural selection favored organisms that could exploit these new opportunities. With less competition and new environments to adapt to, surviving organisms diversified rapidly.
- **Adaptation to New Environments**: Organisms that survived the extinction would have had to adapt to new or changing environmental conditions. These adaptations could include changes in morphology, behavior, and physiology, driven by the pressures of natural selection.
### 2. Evolution of Key Innovations
- **Development of Hard Parts**: One of the most significant developments leading into the Cambrian explosion was the evolution of hard parts, such as shells and exoskeletons. These structures provided protection from predators, support for larger body sizes, and new modes of locomotion. Natural selection would favor these innovations, leading to a rapid diversification of forms.
- **Complex Body Plans**: The evolution of more complex body plans, including segmentation, specialized tissues, and organs, allowed for greater specialization and adaptability. This complexity enabled organisms to exploit different ecological niches more effectively.
### 3. Increased Genetic Variation
- **Gene Duplication and Novelty**: The period leading up to the Cambrian explosion may have seen an increase in genetic variation, possibly due to gene duplication events. These duplications can provide raw material for evolution, allowing new functions to evolve while preserving the original gene's function.
- **Developmental Genes**: Changes in developmental genes, such as Hox genes, which control body plan development, could have led to a greater diversity of morphologies. Small changes in these genes can result in significant changes in body structure and function, leading to the rapid appearance of new forms.
### 4. Ecological Interactions
- **Predation and Arms Races**: The emergence of predators during the Cambrian period created selective pressures for prey to develop defenses, such as hard shells or burrowing behaviors. This predator-prey dynamic likely drove an evolutionary arms race, leading to rapid diversification.
- **Symbiosis and Competition**: Interactions between different species, including symbiosis and competition for resources, would have further driven diversification. Organisms that could effectively exploit resources or form beneficial relationships with other organisms would have been favored by natural selection.
### 5. Environmental Factors
- **Oxygen Levels**: Increases in atmospheric and oceanic oxygen levels during the late Ediacaran and early Cambrian periods provided the energy needed to support more complex and active life forms. Higher oxygen levels would have allowed for larger body sizes and more active metabolisms.
- **Habitat Changes**: Geological and climatic changes could have created new habitats and ecological opportunities. The breakup of supercontinents, changes in sea levels, and the creation of shallow marine environments would have provided diverse habitats for evolution to act upon.
### Summary
Darwin’s theory of evolution explains the transition from the end-Ediacaran extinction to the Cambrian explosion through the mechanisms of natural selection, adaptation, genetic variation, ecological interactions, and environmental changes. These factors combined to create a period of rapid evolutionary innovation and diversification, leading to the emergence of many of the major animal groups we see today.
The "Big Five" mass extinctions (顯生宙 Phanerozoic）
The Phanerozoic is the current and the latest of the four geologic eons in the Earth's geologic time scale, covering the time period from 538.8 million years ago to the present. It is the eon during which abundant animal and plant life has proliferated, diversified and colonized various niches on the Earth's surface, beginning with the Cambrian period when animals first developed hard shells that can be clearly preserved in the fossil record. The time before the Phanerozoic, collectively called the Precambrian, is now divided into the Hadean, Archaean and Proterozoic eons.
In a landmark paper published in 1982, Jack Sepkoski and David M. Raupidentified five particular geological intervals with excessive diversity loss.[2] They were originally identified as outliers on a general trend of decreasing extinction rates during the Phanerozoic,[3] but as more stringent statistical tests have been applied to the accumulating data, it has been established that in the current, Phanerozoic Eon, multicellular animal life has experienced at least five major and many minor mass extinctions.[4] The "Big Five" cannot be so clearly defined, but rather appear to represent the largest (or some of the largest) of a relatively smooth continuum of extinction events.[3] All of the five in the Phanerozoic Eon were anciently preceded by the presumed far more extensive mass extinction of microbial life during the Oxygen Catastrophe early in the Proterozoic Eon. At the end of the Ediacaran and just before the Cambrian explosion, yet another Proterozoic extinction event (of unknown magnitude) is speculated to have ushered in the Phanerozoic.[5]
How to explain the five big extinctions in the Phanerozoic eon? （ChatGPT, 2024-6-27)
The Phanerozoic Eon, spanning approximately 541 million years to the present, has witnessed five major mass extinction events. Each of these events had profound impacts on the diversity of life on Earth. Here’s an overview of these extinctions and their likely causes:
### 1. Ordovician-Silurian Extinction (approximately 443 million years ago)
- **Impact**: About 85% of marine species, including many brachiopods, trilobites, and graptolites, went extinct.
- **Likely Causes**:
- **Glaciation**: A severe ice age caused global cooling and a drop in sea levels, which reduced shallow marine habitats.
- **Sea Level Changes**: The glaciation was followed by rapid warming, causing sea levels to rise and further stressing marine ecosystems.
### 2. Late Devonian Extinction (approximately 372-359 million years ago)
- **Impact**: Around 75% of species, particularly marine life such as reef-builders and brachiopods, were lost.
- **Likely Causes**:
- **Anoxia**: Reduced oxygen levels in the oceans (anoxia) likely played a significant role, possibly due to widespread algal blooms.
- **Volcanism**: Large volcanic eruptions could have released greenhouse gases, leading to climate changes.
- **Meteorite Impact**: Some evidence suggests a potential meteorite impact, though this is less certain than other factors.
### 3. Permian-Triassic Extinction (approximately 252 million years ago)
- **Impact**: The largest extinction event, with around 96% of marine species and 70% of terrestrial vertebrate species going extinct.
- **Likely Causes**:
- **Siberian Traps Volcanism**: Massive volcanic eruptions in what is now Siberia released vast amounts of lava and gases, leading to severe global warming and ocean acidification.
- **Anoxia and Acidification**: The volcanic activity caused ocean anoxia (lack of oxygen) and acidification, devastating marine life.
- **Methane Release**: Possible release of methane from oceanic methane clathrates could have exacerbated global warming.
### 4. Triassic-Jurassic Extinction (approximately 201 million years ago)
- **Impact**: About 80% of species, including many marine reptiles and large amphibians, became extinct.
- **Likely Causes**:
- **Central Atlantic Magmatic Province (CAMP) Volcanism**: Extensive volcanic activity related to the rifting of Pangaea released large amounts of carbon dioxide, causing climate change.
- **Climate Change**: The increased CO2 levels led to global warming, ocean acidification, and anoxia.
### 5. Cretaceous-Paleogene (K-Pg) Extinction (approximately 66 million years ago)
- **Impact**: Around 75% of all species, including the non-avian dinosaurs, went extinct.
- **Likely Causes**:
- **Chicxulub Impact**: A large asteroid impact in present-day Mexico created the Chicxulub crater, causing immediate and long-term climatic effects such as darkness, cooling, and acid rain.
- **Deccan Traps Volcanism**: Concurrent massive volcanic eruptions in India could have contributed to climate change through the release of volcanic gases.
- **Combined Effects**: The combination of the asteroid impact and volcanic activity likely caused drastic environmental changes, leading to widespread extinction.
### Summary
The five major mass extinctions in the Phanerozoic Eon were caused by a combination of catastrophic events and environmental changes. These include volcanic activity, asteroid impacts, climate change, ocean anoxia, and sea level fluctuations. Each extinction event had unique contributing factors, but the common theme is that these events led to rapid and severe disruptions in Earth's ecosystems, resulting in the loss of a significant proportion of species.
Can we halt the sixth extinction, which is going on right now? (ChatGPT, 2024-6-27)
Halting the current, or sixth, mass extinction—primarily driven by human activities—requires concerted global efforts across various domains. Here are some key strategies and actions that could help mitigate biodiversity loss and preserve ecosystems:
### 1. **Habitat Conservation and Restoration**
- **Protected Areas**: Establish and effectively manage protected areas to safeguard critical habitats and biodiversity hotspots.
- **Restoration Projects**: Rehabilitate degraded ecosystems, such as reforesting cleared lands, restoring wetlands, and rehabilitating coral reefs.
- **Sustainable Land Use**: Promote sustainable agricultural, forestry, and urban development practices to minimize habitat destruction.
### 2. **Combatting Climate Change**
- **Emission Reductions**: Implement policies to reduce greenhouse gas emissions, such as transitioning to renewable energy sources, improving energy efficiency, and reducing deforestation.
- **Carbon Sequestration**: Enhance natural carbon sinks through reforestation, afforestation, and soil management practices.
- **Adaptation Measures**: Develop strategies to help species and ecosystems adapt to changing climatic conditions, such as creating wildlife corridors and assisted migration.
### 3. **Sustainable Resource Use**
- **Fishing Regulations**: Enforce sustainable fishing practices to prevent overfishing and protect marine biodiversity.
- **Sustainable Agriculture**: Adopt agroecological practices that promote biodiversity, such as crop diversification, agroforestry, and integrated pest management.
- **Water Management**: Implement sustainable water use practices to protect freshwater ecosystems and ensure the availability of clean water for all species.
### 4. **Pollution Control**
- **Reduce Pollution**: Implement stricter regulations on pollutants, including plastics, chemicals, and agricultural runoff, to prevent ecosystem degradation.
- **Clean-Up Initiatives**: Support and fund clean-up projects to remove pollutants from natural habitats, such as ocean clean-ups and soil remediation.
### 5. **Addressing Invasive Species**
- **Prevention and Control**: Implement measures to prevent the introduction of invasive species and control or eradicate those already established.
- **Biosecurity Measures**: Strengthen biosecurity protocols to prevent the accidental introduction of invasive species through trade and travel.
### 6. **Biodiversity-Friendly Policies and Legislation**
- **Strengthen Laws**: Enforce and strengthen laws and international agreements aimed at protecting biodiversity, such as the Convention on Biological Diversity (CBD) and the Convention on International Trade in Endangered Species (CITES).
- **Incentives for Conservation**: Provide economic incentives for conservation efforts, such as payments for ecosystem services, conservation easements, and ecotourism.
### 7. **Research and Monitoring**
- **Biodiversity Monitoring**: Implement comprehensive monitoring programs to track biodiversity trends and assess the effectiveness of conservation measures.
- **Scientific Research**: Support research to understand the drivers of biodiversity loss and develop innovative conservation strategies.
### 8. **Public Awareness and Education**
- **Education Campaigns**: Raise public awareness about the importance of biodiversity and the actions individuals can take to protect it.
- **Community Involvement**: Engage local communities in conservation efforts, ensuring that they benefit from and actively participate in biodiversity protection.
### 9. **Global Cooperation**
- **International Collaboration**: Foster international cooperation and coordination to address global biodiversity challenges, sharing knowledge, resources, and technologies.
- **Funding and Support**: Mobilize financial resources for biodiversity conservation, including from governments, international organizations, and private sectors.
### Summary
Halting the sixth extinction requires a multifaceted approach that addresses the root causes of biodiversity loss, such as habitat destruction, climate change, pollution, overexploitation, and invasive species. It necessitates strong political will, international cooperation, and active participation from all sectors of society. While challenging, these actions are crucial for preserving the planet’s biodiversity and ensuring the health and resilience of ecosystems for future generations.
