Question

Mass extinetions a. are always caused by asteroid impacts. b. are periods of time in which many species go extinct worldwide. c. have little lasting effect on the history of life. d. affect only terrestrial organisms.

Short answer

b. are periods of time in which many species go extinct worldwide.

Step-by-step solution

Understand the Definition of Mass Extinction

Mass extinctions are events in Earth's history when a large proportion of species go extinct in a relatively short period of geological time.

Evaluate Option (a)

Option (a) states that mass extinctions are always caused by asteroid impacts. This is incorrect because mass extinctions can be caused by a variety of factors, including volcanic eruptions, climate change, and other environmental stresses, not just asteroid impacts.

Evaluate Option (b)

Option (b) states that mass extinctions are periods of time in which many species go extinct worldwide. This is correct because it matches the definition of a mass extinction.

Evaluate Option (c)

Option (c) states that mass extinctions have little lasting effect on the history of life. This is incorrect because mass extinctions have significant lasting effects, often leading to the emergence of new species and altering the course of evolutionary history.

Evaluate Option (d)

Option (d) states that mass extinctions affect only terrestrial organisms. This is incorrect because mass extinctions impact both terrestrial and marine organisms.

Choose the Correct Answer

Based on the evaluations, the correct answer is option (b). Mass extinctions are periods of time in which many species go extinct worldwide.

Key concepts

causes of mass extinctions

Mass extinctions can arise from a myriad of causes. These catastrophic events usually result in the demise of a significant percentage of the planet's biodiversity over a geologically short timeframe. Several factors can trigger mass extinctions, and it's not always the same for every event.

One of the well-known causes is asteroid impacts, which are believed to have caused the Cretaceous-Paleogene extinction event that wiped out the dinosaurs. Asteroids can create massive impact craters and send debris into the atmosphere, leading to drastic climate changes.

Another crucial factor is volcanic eruptions. These eruptions can release large quantities of lava and ash, and more importantly, gases like sulfur dioxide and carbon dioxide. This volcanic activity can result in acid rain, climate cooling (or warming in the long term), and ocean acidification, all of which disrupt the habitat.

Climate change, occurring over shorter or longer timescales, plays a pivotal role. Sudden changes in temperature or weather patterns can be detrimental to species adapted to specific climatic conditions. Additionally, shifts in sea levels can drastically alter marine environments.

Finally, other stressors such as shifts in continental positions, disruptions in ocean currents, and even human activities, especially in the more recent times, pose significant threats leading to mass extinctions.

effects of mass extinctions

The impact of mass extinctions on the history of life and Earth is profound and lasting. These events do not just wipe out a large number of species; they pave the way for dramatic shifts in the planet's ecological and evolutionary landscapes.

Firstly, mass extinctions result in a loss of biodiversity. The elimination of species means that entire ecosystems can collapse, disrupting food webs and ecological interactions. This is not just a short-term effect; the recovery of biodiversity can take millions of years.

However, these catastrophic events also drive evolution. By clearing out dominant species, ecological niches are left vacant. This allows for the rise of new species. For instance, the extinction of the dinosaurs gave mammals an evolutionary advantage, leading to the rise of mammals, including humans.

Additionally, mass extinctions can alter the geographical distribution of species. Surviving organisms may migrate to new habitats, leading to a redistribution of life forms on Earth.

Lastly, mass extinctions can change the course of biological evolution substantially. They serve as major turning points, leading to shifts in dominant species and the emergence of new life forms that can adapt to the newly altered environments.

types of organisms affected

Mass extinctions do not discriminate; they impact a broad range of organisms across different environments. Both terrestrial and marine life forms are affected.

On land, plants and animals can face massive die-offs. For instance, during the Permian-Triassic extinction, also known as 'The Great Dying,' it's estimated that about 70% of terrestrial species disappeared. This included a vast array of both flora and fauna.

Marine organisms can be equally devastated. During the same Permian-Triassic event, around 96% of marine species went extinct. Coral reefs, fish, mollusks, and various planktons, which form the base of aquatic food webs, suffered substantial losses.

Furthermore, microorganisms such as bacteria and fungi, crucial for nutrient cycling, can also be heavily impacted. These microorganisms ensure the continuity and health of ecosystems by decomposing organic matter and recycling nutrients.

In summary, mass extinctions cut across all life forms, from the smallest microorganisms to the largest terrestrial and marine animals. This comprehensive devastation underscores the profound impact these events have on the entirety of Earth's biosphere.