Mass Extinctions – A Level Geology OCR Revision

Defining Mass Extinctions

Comprehend mass extinctions as periods in geological history where a significant proportion of life on earth is wiped out in a short time period, often as a result of a catastrophic event.
Distinguish these from background extinction rates, which refer to the standard rate of extinction seen over geological time.
Familiarize yourself with the Big Five Mass Extinctions, namely, the End Ordovician, Late Devonian, End Permian, End Triassic, and End Cretaceous extinctions.

Recognize that plate tectonics, volcanism, asteroid impacts, climate change and other environmental shifts might serve as potential triggers for mass extinctions.
Understand how massive volcanic eruptions like flood basalts could impact climate and life, driving mass extinction events.
Evaluate the role of climate change and ocean acidification, often resulting from enhanced volcanism or even asteroid impact, as drivers of mass extinction.

Learn how to identify sudden changes in sedimentary facies, fossil abundance or depletion, and elevated levels of certain elements like iridium in sedimentary layers, which serve as indicators of mass extinction events.
Understand how biostratigraphy, the use of fossil evidence to date and interpret sedimentary layers, can help establish the occurrence, duration and aftermath of mass extinctions.
Realize that the effects of mass extinctions can dramatically alter patterns of sedimentation and result in the formation of specific geological features (e.g. boundary clay at the K-T boundary).

Consider how the death and decay of large amounts of biological material can contribute to organic-rich sediments and the formation of petroleum source rocks.
Recognize that shifts in life forms, following a mass extinction, may significantly alter sedimentation patterns in a basin.
Understand that mass extinction events can provide a time marker in the stratigraphic record, assisting in relative dating of sedimentary sequences.

Recognize how these extinction events punctuate the evolution of life and have led to significant changes in Earth’s biodiversity.
Understand how mass extinctions foster adaptive radiations, where surviving species diversify to fill newly vacant ecological roles.
Review how the most severe extinction event, the End Permian, resulted in the loss of some 95% of marine species, resetting life’s evolutionary course.