Lecture 10: The Proterozoic

This flashcard set covers the Paleoproterozoic, Mesoproterozoic, and Neoproterozoic eras, highlighting key events such as supercontinent formations and the evolution of life. It provides insights into major geological changes and biological developments during these critical periods in Earth's history.

Paleoproterozoic Era (2.5-1.6 Ga)

Paleoproterozoic Era (2.5-1.6 Ga)

Period characterized by early plate tectonics, orogenic belts, and the Wopmay Orogeny.

Mesoproterozoic Era (1.6-1.0 Ga)

Period marked by the separation of Nuna, Grenville Orogeny, and the Midcontinental Rift.

Neoproterozoic Era (1.0-0.54 Ga)

Includes the Rodinia and Pannotia supercontinents, Neoproterozoic glaciation, and possible causes of glaciation.

Archean-Proterozoic Boundary

Marks approximate time of changes in style of crustal evolution.

Archean Rock Groups (4 G’s)

Gneiss, Greenstone, Graywacke, Granite; represent different rock types from the Archean era.

Crustal Evolution

Describes the changes in plate tectonics from Archean to Proterozoic, including hotter, thinner crust in Archean.

Evidence of Life Evolution

Life evolved from simple prokaryotes in the Archean to more complex eukaryotes and eventually multicellular metazoans in the Proterozoic, showing increasing complexity.

Glacial Deposits in Late Proterozoic

Included poorly sorted sedimentary rocks, tillites, and dropstones, deposited in old ocean basins, shallow seas, continental shelves, and sedimentary basins.

Proterozoic Atmosphere

Earth's atmosphere during the Proterozoic had more oxygen compared to the Archean, evidenced by Banded Iron Formations (BIFs) and changes in rock formations and fossils.

Albedo feedback loop

A process that intensified global cooling by increasing ice cover, which reflected more solar radiation and further lowered temperatures, leading to even more ice formation; positive feedback.

Banded Iron Formations (BIFs)

Alternating layers of iron-rich material and chert, indicating vigorous photosynthesis.

Boring Billion

During this time, there is very little that occurs in the atmospheric evolution over the Mesoproterozoic; little oxygen production.

Dropstones

Large rocks that are found embedded in sediments that were deposited by glaciers or ice sheets.

Ediacaran Fauna

Group of ancient, soft-bodied organisms representing some of the earliest known complex life forms, mostly known from fossil impressions in rocks.

Eukaryotes

Organisms with cells containing a nucleus and organelles, reproducing sexually and requiring oxygen for metabolism.

Failed mid-continental rift

A significant geological feature in North America that represents an ancient, incomplete rift system.

Gneiss

Metamorphic rock; early cratons, strongly heated and deformed granite that contains banding.

Granite

Igneous rock; late-stage intrusions into the other structures.

Graywacke

Sedimentary rock, sandstones and muds from early oceans.

Greenstone

Metamorphic rock; metamorphosed proto-oceanic crust, or early oceanic crust.

Grenville Orogeny

Major mountain-building event during the Mesoproterozoic (~1.3-1.0 Ga) where ancient continental plates collided, forming the Grenville Mountains.

Laurentia

A large landmass that was part of the ancient supercontinent Rodinia; the craton (nucleus) that eventually became the core of North America.

Nuna

The first recognized supercontinent.

Obliquity

The angle between a planet's rotational axis and its orbital plane; the tilt.

Orogeny

The process of mountain building; happens when tectonic plates collide, fold, and push up the Earth's crust, creating mountain ranges and other large geological structures.

Pannotia

3rd supercontinent; formed from the reassembly of the separated pieces of Rodinia.

Polish

Describes the smooth, shiny surface left on rocks by the abrasion of a glacier dragging sediment and debris over them.

Prokaryotes

Simple, single-celled organisms that lack a nucleus

Rodina

2nd supercontinent of Proterozoic formed (~900 Ma); consisted of crustal segments of Antarctica, Australia, Laurentia, and S. China.

Snowball Earth

Period about 2.3 billion years ago when Earth was covered in ice, leading to a frozen planet; Huronian Glaciation (Gowganda Ice Sheet, first snowball hypothesis).

Striations

Parallel lines or grooves carved into rocks by the movement of glaciers; show direction and strength of glacial movement.

Stromatolites

Layered, rock-like structures formed by cyanobacteria; these organisms build up layers of sediment and minerals over time.

Supercontinent

Massive landmass formed by the merging of multiple continents, including Nuna (Paleoproterozoic), Rodinia (Neoproterozoic), and Pannotia (Neoproterozoic).

Tillites

Unsorted, lithified, glacial debris

Varves

Mudstone seasonal laminations providing a record of past climate conditions.; may include dropstones.

Wilson Cycle

Theory explaining the formation and closure of ocean basins over millions of years, involving processes like rifting, expansion, subduction, and collision.

Wopmay Orogeny

A geological mountain building event where tectonic activity in what is now northwestern Canada led to the formation of the NW Canadian Shield; played a key role in the formation of the ancient continental crust in the region.

Metazoans

Multicellular animals with specialized cells organized into tissues and organs, appearing in the fossil record.

Midcontinent Rift

Large geological rift in the Mesoproterozoic (~1.2-1.1 Ga) where the North American continent began to split apart but failed to fully open into an ocean.