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Life and Extinction on Earth
In ~ 1.5 hrs!
Life and Extinction on Earth
From: Sepkoski and Raup, 1982; Erwin et al., 1987
Diversity over time: Marine organisms
(1) Diversity of life
(2) Geologic Time
On Geologic Time
• Geologic Time is defined in two fashions: absolute (radioactive dating) and relative (use of stratigraphy, index fossils, etc.).
• Again we have James Hutton to thank for this and for Plutonism, plus a few others!
• Key point about relative dating—it depends on an understanding of basic principles of geology. Whereas absolute data mainly depends on isotope geochemistry.
On Geologic Time
• Complication: Rock record is not always continuous on Earth. Strata laid down horizontally, but unconformities exist. These are due to many causes such as transgressions and regression of sea level. Also affected by igneous activities.
On Geologic Time
• Nicholas Steno: He carved into rock three governing principles of geology (circa 1669).
– 1. Principle of superposition– 2. Principle of original
horizontality– 3. Principle of original lateral
continuity
• Robert Hooke: Fossils were organic, potential biomarkers, and not deposited during the Great Flood!
On Geologic Time
• Sir Charles Lyell (1797-1875): He wrote Principles of Geology (circa 1830 and revised into 1872).
– He built upon Hutton’s ideas to produce the first comprehensive view of modern geology.
On Geologic Time
• Importance of fossils:
1. A direct record of ancient life and record evolutionary change of life on Earth.
2. They are recorder paleo-environments, communities, and climates.
3. Are of great utilitarian value for correlation of strata.
On Geologic Time
Life and Extinction on Earth
From: Sepkoski and Raup, 1982; Erwin et al., 1987
Diversity over time: Marine organisms
(1) Diversity of life
(2) Geologic Time
Life and Extinction on Earth
Diversity over time: Marine organisms
Life and Extinction on Earth
Diversity over time: Marine organisms
On Geologic Time
• Significance: Record abundant oxygen in sea water argued to be released by photosynthetic cyanobacteria. This combined with iron.– Approximately 3 to 1 Gy.
• Thus life was present in abundance before the formation of the precursors to these rocks.
On Geologic Time
• At what time did life evolve on Earth?
– The ‘real’ date is very debatable. It runs from 3.8 to 4.2 Gy.
Evolution
• From a geologic perspective, evolution is a point of fact, not a theory.
• How evolution occurs is up for debate.– Darwinism– Punctuated equilibrium– Red Queen Hypothesis
Life and Extinction on Earth
Diversity over time: Marine organisms
Big eventSomething big happened between ~540-600 My
On Geologic Time
• Big Event at the Precambrian – Cambrian boundary:
– Exoskeleton! This changes the face of the Earth!
• Up till this time period, very little evidence for skeletal components.
Life and Extinction on Earth
Diversity over time: All major groups of life.
Life and Extinction on Earth
Diversity over time: Something changed!
Life and Extinction on Earth
From: Sepkoski and Raup, 1982; Erwin et al., 1987
Background vs. mass extinction
Either big 6 or…
Life and Extinction on Earth
• Mass extinction: A catastrophic event for the worlds biota that eliminates some percentage of organisms (at many taxonomic levels) from the gene pool– Must be catastrophic.– A lot of life goes extinct.– And the life must have
belonged to different phyla, habitats (entire communities also go extinct), and be global.
– Rapid!
Life and Extinction on Earth
…big 5!
Background vs. mass extinction
Causes?
Life and Extinction on Earth
Background vs. mass extinction
Life and Extinction on Earth
• Causes of mass extinction:– Intrinsic
– Extrinsic
• We will discuss these a little later in the lecture.
Life and Extinction on Earth
• C-O = Significant number of trilobites, brachiopods, and conodonts go.
• O-S = ~ 27% families, 57% genera.
• D - Crb = ~ 19% families, 57% genera, 70% spices.
• P- Tr = ~ 57% families, 80% genera, 98% species.
• Tr –J = 23% families, 50% genera
• K - Ter = ~ 17% families, 50% genera, 75% species.
Life and Extinction on Earth
• Causes of mass extinction:– Intrinsic– Extrinsic
• Intrinsic issues such as stagnate gene pools, normal evolution, etc.
• Extrinsic depend on some geological cause such as global volcanic activity, plate tectonics, sea level changes, global climate change, or impacts etc.
– Discussion of communities of organisms, ecosystems.
Real diversity of time?
On Geologic Time
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