6 Geologic Time and Life in the Oceans - Tulane University

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EENS/EBIO 223 Professor Rosenheim

Geologic Time and Life in the Oceans


Oceans and Life

• Oceans are the birthplace of “life.”Life – metabolism, growth, reproduction, response to stimuli

Metabolism – use of energy stored in ambient chemicals

Reproduction – production of viable offspring with similar to identical charactisteristics


How Old is Earth? The Solar System?

• Archbishop Usher of Armagh, Ireland (1581-1656)– Earth created at 9:00 AM on October 26, 4004 BC– Eastern Standard Time or Rocky Mountain Time?

• 1800’s - physicists and geologists realize Earth must be very old– Halley (1715) - Salinity of oceans increased with

time – Joly (1899) calculated an age of 90 million years– Lord Kelvin estimated the age of Earth 24 to 40

million years old, based on how fast it cooled down, but he was wrong.

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Geologic Time

• Relative Dating– Older, younger– Correlation

• Absolute Dating– Measuring years before present– Years after a specific event


Relative Dating

• Fossils are generally contained in sedimentary deposits

• With time, new fossils are deposited on top of old fossils


Relative DatingA

B

C

D

E In what order did these features form?

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Relative Dating

• Correlation– Relating common

sediment strata over great distances

– Fossils, lithology, – Stratigraphy


Absolute Dating

• Radioactive Elements provide a natural clock

• Most elements are stable, but some are not. Formed during differentiation of the planet and perhaps from supernovae, they gradually decay into other stable elements


Atoms and Molecules

• A (not) – tomos (cut)– Fundamental building block of matter

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Radioactive Decay


Radioactive Decay

Gamma (γ) decay

Alpha (α) decay

Marie and Pierre Curie (above) and Henri Becquerel (left) were awarded a joint Nobel Prize in 1903 for their discovery of radiation.


Radioactive Decay

Rutherford observed that matter consisted mostly of empty space. He is the father of nuclear physics.

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Radioactive ClocksOnce these elements are incorporated into a rock through deposition or crystallization, the clock is set. Knowledge (or an assumption) of the initial amount of daughter isotope coupled with measurement of the current parent/daughter ratio enables an age calculation.

NdtdN λ−= where N is number of radioactive nuclei and λ is the

radioactive decay constant.

dtNdN λ−= or 0loglog NtN ee +−= λ

)exp(0 tNN λ−=


Radioactive Decay


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Uranium/Thorium Dating

• 238U, 232Th, 235U – primordial elements in Earth’s crust– λ238 = 4.5 x 109

– λ232 = 1.4 x 1011

– λ235 = 7.0 x 108

• Clock set at crystallization (igneous rocks) or precipitation (marine carbonates)


EarthEarth is an active planet and its Earth is an active planet and its original surface rocks no longer original surface rocks no longer exist.exist.•• The oldest rocks have been The oldest rocks have been dated to 3.8 dated to 3.8 GaGa•• Moon rocks have been dated to Moon rocks have been dated to 4.2 4.2 GaGa••Meteorites that have struck Meteorites that have struck Earth have been dated 4.5 Earth have been dated 4.5 -- 4.6 4.6 GaGa


Radiocarbon Dating• 14C half life = 5,730 y• Useful for once-living

materials• Constantly produced by

bombardment of 14N (70% of atmosphere) by cosmic rays

• Clock is set when organism ceases to photosynthesize/ metabolize new carbon.

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Constructing the Geologic Time Scale

• Early Time Scale– Based on rocks, fossils and correlations– Relative Time– Classification into Eons, Eras, Periods

• Later Time Scale– Radiometric techniques applied to existing

rocks


Geologic Time

• Based on fossils, extinctions, correlations


Geologic Time

• Based on fossils, extinctions, correlations

• More recent rocks have eroded less – more divisions of time recently

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Ocean Life

• Archean and Proterozoic Eons


3.17 billion years

Most of life’s history of development occurred slowly in the oceans.


Primordial Soup• Water on Earth’s surface collected ever more

complex compounds (amino acids) which were fused to proteins by lightening and UV light

• 3.6 billion years ago - Ga

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Experimental Demonstration

• Stanley Miller (chemist) and Harold Urey (physicist)


Why Water?

• Water is an excellent solvent.• Early oceans facilitated interaction

between dissolved chemicals.• Living entities need some form of a solvent

for biochemical reactions – those that produce energy for life – and water is one of the best known solvents (others may be comparable at different pressures and temperatures).


Early Life• Theory – Membranes developed first to maintain

a constant primordial soup-like microenvironment.

• Theory – Heterotrophs probably existed first, processing non-living organic material around them.

• Theory - Autotrophs probably developed later, with the advantage that they could use constant energy sources (sun, hydrothermal, etc.)

• First life – 3.6 billion years ago (Ga)

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Harnessing Energy

• Photosynthesis– Use of light energy (sun) and raw materials

(nutrients) to grow and reproduce

• Chemosynthesis– Use of chemical energy (inorganic compouds

at hydrothermal vents) in absence of light to grown and reproduce

Tube worms at a vent


Earliest Cyanobacteria

• Stromatolites• Layers of algae and

sediment• Evident in geologic

record• 3.5-3 Ga


Evolution from Early Life

• Oxygen crisis– Photosynthetic organisms filled atmosphere

with O2, after they oxidized all surface rocks• 1.5 Ga after first life• O2 from water – water was everywhere

– Ozone formation stopped UV light – and formation of anaerobic bacteria’s food

– Major extinction of anaerobes, but evolution to more efficient life (aerobic bacteria)

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Oxygenation of Earth’s Atmosphere


Cambrian Explosion


Cambrian Explosion580-530 Ma

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Reasons for the Cambrian Explosion

• Climate change• Predation• Plate Tectonics• These are some theories – the jury’s still

out


Ordovician LifeSponges and bryozoans, jawless fish, corals


Silurian LifeAppearance of fish, continued development of Ordivician life forms in shallow inland seas

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Devonian LifeAbundance of corals and coral reefs. Land plants and amphibians, as well as land insects


Carboniferous LifeVery high productivity in shallow inland seas. Large coal deposits date to this period. Crinoids dominate the marine fossil record.


Permian LifeAbundant coral reefs, featuring sponges and clam-like animals. Large reptiles on land, paving way for dinosaurs

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Permian Extinction95-99% of all marine species become extinct. Land species keep diversifying and evolving. Larger than the extinction of the dinosaurs!

Reasons:

•Conglomeration of the continents – reduction of shallow seas

•Snowball Earth – a worldwide glaciation

•Anoxia in the oceans

•Volcanic eruptions

•Impact event – would a crater still exist?


Mesozoic Sea LifeMesozoic (middle animals) – Age of the dinosaurs


Cenozoic Sea LifeThe last 65 My. Demise of the ocean lizards. Evolution of marine mammals, entering seas from land. Evolution of many modern species in concert with very old species.

PlakicetusMesonychid (53 Ma)

Ambulocetus

Protocetid

Basilosaurus (38 Ma)

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Summary

• Key Terms and Concepts– Cambrian Explosion– Radioactive Decay– Relative Dating– Oxygen Crisis– Permian Extinction

6 Geologic Time and Life in the Oceans - Tulane University

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