Lecture 2: Historical Geology and Geologic Time

Neptunism, Plutonism, and More

• Abraham Gottlob Werner

  • 18th-century German geologist and mineralogist

  • Best known for his Neptunism theory,

  • Neptunism: the geological theory that all rocks originated from sedimented deposits of minerals in the Earth’s oceans.

• James Hutton

  • Father of Geology

  • Best known for his theory of uniformitarianism and for proposing the concept of deep geological time.

  • Plutonism: the geological theory that rocks, especially igneous rocks, form from the cooling and solidification of molten magma beneath the Earth's surface.

  • Siccar Point outcrop and unconformity - deduced that all we see on this planet could be explained by these processes and time.

• Uniformitarianism: the principle that the same natural laws and processes that operate in the universe now have always operated in the past. It suggests that geological processes observed today can be used to interpret past geological events. This concept emphasizes consistency over time.

• Actualism: The natural laws and processes we observe today have always operated throughout Earth's history. Unlike uniformitarianism, it recognizes that the rates and intensities of these processes can vary over time, applying current natural laws to past events without assuming constant rates.

• Charles Lyell

  • Formalized the concept uniformitarianism: the uniformity of natural processes through time.

  • Championed for uniformity of processes, not just in frequency but in intensity.

  • Described how geologic features cut across rock is younger than rock itself (ex: paper)

  • Highlighted relative dating

• Nicholas Steno

  • Father of Stratigraphy

    • Strata, layers, must preserve a disciple chronological history of our planet

  • Recognized that not all layers of rock had formed at the same time; changes in conditions led to changes in rocks

  • Fossils formed at same time as the rocks

  • Proposed basic principles we still use today

    • Superposition, cross cutting, principle of inclusion, original horizontality

• William Smith

  • Created the first geological map, primarily using fossils as a basis.

  • Observed that fossils appeared in a predictable vertical order.

  • Used fossil evidence to determine the correct positioning of rock layers.

  • Noted that fossils found in lower layers were less familiar compared to those in upper layers.

An Introduction to Time

Geologic Eons

• Eons: The largest divisions of geological time, spanning billions of years.

• Hadean

  • Beginning of Earth’s formation

• Archean

  • Plate tectonics being

  • Rock formation

  • Earliest evidence of life (stromatolites)

• Protozoic

  • Evolution of atmosphere and biosphere

  • BIFS: Banded iron formations, has alternating layers of iron oxides and iron-poor chert

• Phanerozoic

  • Complex life begins

Phanerozoic Eras

• Paleozoic

  • Trilobites, shallow seas, Pangea (supercontinent)

• Mesozoic

  • Dinosaurs, erg of sand, western orogeny’s

  • Erg means sand sea or dune sea, little vegetation

  • Orogenesis - mountain forming event

• Cenozoic

  • Present

Phanerozoic Periods

• From oldest to newest:

  • Cambrian

  • Ordovician

  • Silurian

  • Devonian

  • Mississippian

  • Pennsylvanian

  • Permian

  • Triassic

  • Jurassic

  • Cretaceous

  • Paleogene

  • Neogene

  • Quaternary

Geological Events in Human History

Event 1: Krakatoa

• Volcanic eruption

• Convergent plate boundary

• When ocean crust collides with continental crust, the denser stuff sinks down and that’s where subduction comes from.

• Subduction zone → the most likely cause to form volcanoes/ the melt that energy forms as lava onto the surface

• Australian plate subducts under the Eurasian plate

• Water is pulled down and turned into steam, which add volatiles. The added volatiles to the rock changes the melting temperature and then we get magma that rises to the surface.

• Resulted in Tsunami

Event 2: Mt. Vesuvius

• Volcanic eruption

• Africa and Eurasian plate convergence

• Buried City of Pompeii

• Earthquakes, gases, ash, mudflows

Event 3: Santorini

• Convergent plate boundary

• Africa and Eurasian plate convergence

• Three to four rimes the magnitude of Krakatoa

• Likely ended the Minoan civilization

Event 4: East African Rift Valley

• Continent is splitting apart

• Wet volcanic ash preserves the footprints of elephants, three toed horses, saber-toothed cats, insects, and millipedes.

• Preserves footprints of two individuals of Australopithecus afarensis (same species as the Lucy fossil).

  • Walking side by side and straight up

Event 5: Australopithecus Tracks

• Tracks found by Mary Leakey resolved an issue of early humankind

• Did evolution of the brain lead the way to walking upright or vice versa?

• Walking upright lead to brain development OR brain development lead to walking upright.

• Other Dramatic Geologic Events

• San Francisco Earthquake of 1906

• Alaska Earthquake of 1964

• Japan Tsunami of 2011

Climate

• Prior to 10,000 years ago the Middle East was humid, fertile place.

  • Earliest evidence for human civilization exists here.

  • After 10,000 years ago as the Ice Ages waned the area became the harsh desert it is today.

  • People of this region had to cram in the permanent river valleys.

• Since the 1890’s records have shown a progressive rise in sea level.

  • With modern observations there is little doubt why.

  • Glaciers are melting on a scale of our life-times.

  • The minimum calculation for sea level rise if Greenland and the west Antarctic ice sheets melt is 50 meter rise in sea level.

Rapid, Violent Geologic Processes

• Ancient people were impressed by rapid, violent geologic processes.

• Led to a view of the Earth that change occurs catastrophically and rapidly.

• View predominated European thought until the 1850’s.

• Coincident with a young Earth view perspective.

Geology as a Science Begins to Take Off in Europe in the 1800’s

• Geologists began to observe processes at work today (e.g., James Hutton, 1788)

  • He was the first to bring up the idea of deep time.

• Siccar Point - deduced that all we see on this planet could be explained by these processed and time.