Earth History 89.331 Course information Prof. Lori Weeden Office: Olney 402b Office phone: 978-934-3344 Lori_weeden@uml.edu Course web page: http://faculty.uml.edu/lweeden/earthlife.htm
Earth System History Fourth Edition by Steven M. Stanley and John A. Luczaj Chapter 1
The Earth is like a book.. A REALLY old book.. And it has taken some sophisticated investigation to read its stories
The Earth is old REALLY old. The Earth as we know it has taken a really, REALLY long time to develop. Humans are the rookiesthe new species that has been around for just a blink of geologic time. There have been a lot of steps taken along the way. In fact, if you were to consider Earth s time in the context of a 365 day calendar year it would look something like this
Millions of Event On the Calendar years ago 4567 Earth Forms Jan. 1 4400 Oldest Dated Minerals Jan. 15 4000 Oldest Dated Rocks Feb. 16 3500 First fossil evidence of life (prokaryotes no nucleus) Mar. 28 2100 First evidence of eukaryotic cells (have nucleus) July 18 750 Snowball Earth Nov. 1 670 Earliest known multicellular organisms Nov. 8 545 Cambrian Explosion of multicellular life Nov. 18 505 Fish evolve Nov. 21 440 Plants invade the land Nov. 27 380 Vertebrates invade the land Dec. 1 365 First seed plants (ferns) Dec. 3 330 First possible reptiles Dec. 5 260 First ancestral mammals Dec. 11 251 Permian Extinction Dec. 12 230 First Dinosaurs Dec. 13 155 First birds Dec. 19 120 First flowering plants Dec. 22 65 K-T Extinction Dec. 26 6 Earliest hominids (ancestors to humans) Dec. 31 2:00 pm 3 North America first glaciated (Glacial Epoch begins) Dec. 31 7:00 pm 0.1 First anatomically modern Homo sapiens Dec. 31 11:48 pm
When time is this vast, we break it up into pieces or categories: Eon: the largest formal unit of geologic time *Precambrian (subunit)--archean (subunit)--proterozoic *Phanerozoic Era: The three primary intervals in which the history of life on Earth serves to define *Paleozoic *Mesozoic *Cenozoic Periods: significant intervals within an era Epochs: significant intervals within a period
The Earth is constantly changing
Geologist of today follow several rules the foremost being that of Actualism: The notion that the fundamental physical and chemical principles that humans observe operating today have operated throughout Earth s history.
Nicolaus Steno s three principles pertaining to sedimentary rocks: A. Principle of Superposition B. Principle of Original Horizontality C. Principle of original lateral continuity
Additional geologic principles.. Principle of Cross-cutting relationships Principle of fossil succession Principle of Inclusions
Basic Characteristics of the Earth, a review: Isostasy: the state of gravitational equilibrium between the earth's lithosphere and asthenosphere such that the tectonic plates "float" at an elevation which depends on their thickness and density
Plate Tectonics Review..
It is easy to see the igneous and metamorphic sections of the rock cycle embedded within the plate tectonics model, but what about sedimentary?
Water, water everywhere. Water is the primary erosion agent on Earth. It is through the interaction with water that sediment, and minerals are distributed and deposited. (although wind is also responsible for some sediment transport)
Episodic deposition and scour of an ancient streambed. Turbidite beds
Angular unconformity between Old Red Sandstone and Silurian rocks and Siccar Point, Berwickshire, Scotland. The place where James Hutton recognized the possibility of an unconformity.
Now, let s do an exercise to see if we understood the geologic principles and unconformities. List the beds and events in order from oldest to youngest and identify the unconformities. E, erosion, nonconformity, L, C, uplift, fault (H), erosion, angular unconformity, M, D, J, A, erosion, disconformity*, N, K, B, uplift, erosion, angular unconformity, F, erosion. *although the contacts between N and A represents a nonconformity.
This concludes Chapter 1 Please complete Review Questions: 1, 2, 6, 7, 9 & 11 We will begin Chapter 5: Sedimentary Environments next class period. I strongly encourage you to read ahead.