Historical Geology - Hadean and Archean Flashcards
How is the Hadean Eon described?
- named after Hades
- no rocks Earth this old except some meteorites and isolated Zircon crystals.
- provides an estimate of the age of the solar system and the planets within it.
- during the early Hadean the solar system was forming.
Explain the Accretion Disk.
- The sun was formed by gasses getting trapped in a self-gravitational collapse until it began to undergo nuclear fusion and give off light and heat.
- Surrounding particles began to coalesce due to gravity into larger lumps or planetisimals, which continued to aggregate into planets
Explain stratification of the earth.
- center is called the core - surrounded by the mantle - surrounded by the lithosphere (upper mantle and crust)
What is a meteorite and what can it be made of?
A solid piece of debris that survives the fall to earth. It can be made of stone (most common) or can be metallic or a combination of both.
- many meteorites fell early on which scientists believe accounts for most of the heavy metals found on the surface of the earth.
Describe Earth during Hadean?
- atmosphere was different from today
- Earth’s crust cooled enough that rocks and continental plates began to form
What are possible causes for the formation of the moon?
- asteroid captured by earth’s gravitational field
- portion of earth knocked loose by a large impact
What formed the ocean?
- formed mostly from water vapor emitted during volcanism
- salts derived from weathering
What formed the Earth’s atmosphere early on?
- composed primarily of volcanic gasses
- O2 was produced in very small quantities
Discuss the origins for the continental crust. (What it was made of)
- original crust would have been largely mafic (rich in magnesium and iron) in composition
- Felsic (feldspar and quartz) minerals formed from mafic slabs that were partially melted upon subduction
How is the Archean Eon characterized?
- derived from Greek “arche” which means “beginning” or “origin”
- continents were small and thinner than post-Archean continents.
What is a protocontinent?
An actual or hypothetical landmass that might later be enlarged into a major continent or broken up into smaller one.
What is a craton?
Old stable portion of the continent.
What is a greenstone belt?
- a block of lithosphere that has been attached to a craton (stable rock) while preserving its geologic history
- zones of variably mafic rock that occur within Archaean and Proterozoic cratons between granite and gneiss bodies. It is primarily formed of volcanic rocks, dominated by basalt, with minor sedimentary rocks inter-leaving the volcanic formations.
- Protocontinents accrete (form) during Archean to form continental cratons.
- Rock deposits by Archean volcanic arcs in a series of terranes
- Pillow basalt structures and fine-grained sedimentary rocks
What are the two most abundant gasses in the Earth’s atmosphere?
N2 and O2
How was the majority of the O2 in the earth’s atmosphere produced?
Photosynthesis