Flashcards
Archean History (13)
Cards in this deck (14)
- 1Why is relatively little known about Archean history?Archean rocks are uncommon & deeply buried & often intensely metamorphosed
- 2When was impact cratering most intense in Earth history?-Before ~4.2 Ga
-Earth & inner solar system got bombarded - 3Did the early Earth have a high heat flow during the Archean?Yes
~2-3x greater than now - 4What are the implications of high heat flow?There were lots of hotspots & rifting
- 5☼What did early continents start out as?☼ ☼What were they called?☼-Small, thin blocks
-cratons or "protocontinents"
(All Archean in age) - 6How did early continents grow?-They moved, collided, got sutured (collide and stick.)
-This caused them to slowly grow in size - 7Did any supercontinents form during the Archean?-Yes
There was a suspected continent named Ur
~3 Ga - 8What is the significance of continents?Once stable continents formed, they became sites for weathering, erosion, and deposition of sediments.
(Start of the Sed. Rock record) - 9How old are the oldest known Earth rocks & minerals?-oldest rock: 4.28 Ga, from the eastern side of Hudson Bay, Canada
-oldest mineral: 4.404 Ga, a zircon crystal from the Jack Hills of Western Australia
- ~4.5 Ga Earth rocks are inferred to be present underneath Baffin Island in Arctic Canada, based on studies of lavas there - 10Archean rocks are mostly what, in terms of igneous, metamorphic, and sedimentary?Mostly metamorphics
-Lots of lots of gneisses from cooked protocontinent rocks & lots of greenstone belt rocks from cooked oceanic crust & oceanic lithosphere - 11When & where was the oldest known Ice Age (glaciation)?-2.9 Ga
-Pongola Basin, South Africa - 12What are BIFs?Banded Iron Formations
-Iron-rich, marine, sedimentary rock, now metamorphosed - 13When do BIFs first appear?Neoarchean
(new/end of Archean) - 14☼What was the temperature of Archean climates and seawater compared to now☼?They were very hot and hot (respectively)