2 pages report - Cardillac Desert book

Lecture 3 - Water on Earth

Formation of Earth Origin of water

Distribution of water

Atmospheric circulation

Water cycle

Formation of Earth

Formation of Earth

Coalescence of silicate material. Cool.

Then heating by: 1) meteorite impact 2) gravitational compression (potential energy) 3) decay of radioactive elements (not a lot of material, but packs a wallop).

The heating caused the segregation of the Earth’s core, which concentrated iron. Caused melting or iron-nickel and formation of core. The ‘falling’ of this iron core would cause a heating increase of over 2000°C.

Planetary differentiation is the most significant event in the history of the Earth. Caused ‘resetting’ of the planet.

Differentiation of Earth

. Originally a homogeneous agglomeration

. Temperature more than enough to melt rocks

o Collision/impact kinetic energy

o Radioactive decay of:

. Uranium (U)

. Thorium (Th)

. Potassium (K)

Two times or ways to differentiate the Earth

. Hot accretion (most likely)

o High energy of impacts already melted & differentiated planetesimals

or

. Cold accretion

o Melting & differentiation soon after accretion by radiogenic heat

Introduction:  Water Web— Connected Californians;

TAPPING INTO A PLANETARY CYCLE:  A Great Water Wheel;  Vital Molecule; “Normal” Weather —Anything But “Average”; 

CALIFORNIA WATER LANDSCAPE:  Pristine Waterscape; Groundwater; Hydrologic Regions: 

[email protected]>

Compositional Structure (layering)

o Developed because of density differences between compounds

o Core

. Iron melting (iron catastrophe) by 4.5 Ga!!

. Fe is ~1/3 mass of Earth

. Sinking of molten iron releases potential energy (additional 2000˚ C of heat)

. Formed Fe/Ni (+ S) core

. Density = 11-12 g/cm3

The earth condensed in four basic steps. 1) It began to accrete from the nebular cloud as particles smashed into each other forming so- called planetesimals. 2) As the mass of the Earth grew so did it's gravitational force and the Earth began to compress itself into a smaller and denser body. This happened about 4.5 billion years ago. 3) In the third step the compression itself began to heat the interior of the Earth; also there was heat generated by radioactive decay. The interior of the earth began to melt. Because iron is the heaviest of the common elements that make up the Earth, as the Earth began to melt droplets of melted iron began to sink towards the center of the earth. 4) Proceeding slowly at first it sped up to catastrophic proportions - hence it is called the iron catastrophe.

Homework 1 – due Jan 23rd [email protected]

Earth Cooled Rapidly! • Evidence suggests Earth had

cooled substantially by 4.4 BYA • Evidence for liquid water 4.4 BYA • Some continental crust formed (4.4

BYA) • Bombarded by meteorites (until 3.8

BYA) • Initial atmosphere and hydrosphere

contain NO O2, that is molecular oxygen that sustains many forms of life on the planet today!

Evidence for “Cool” Earth with a Hydrosphere 


• Oldest Rocks: 4.03 Billion Year Old Acasta Gneiss, Canada

(granitic composition metamorphic rock)

• Oldest minerals: 4.4 Billion Year Old Zircons from Jack Hills – Composition indicates water present

Early Atmosphere: Steady addition of gasses from volcanic emissions

• Carbon Dioxide • Methane • Water vapor • Nitrogen • Carbon Monoxide • Sulfur-rich

gases

Acidic rains interact with hot rocks

Atmospheric Evolution

1. primordial gases, later lost from sun's radiation

2. exhalations from the molten surface (volcanic venting); bombardment from icy comets

3. steady additions of carbon dioxide, water vapor, carbon monoxide, nitrogen, hydrogen, hydrogen chloride, ammonia, and methane from volcanic activity

4. addition of oxygen by plant/bacterial life

Earth’s Early Ocean • H2O is the most abundant

gas released by volcanoes • Evidence for liquid water

present very early in Earth history (4.4 Ga)

• Some (<3%?) of water contributed by icy comets

• No O2 dissolved in oceans – dissolved Fe2+ makes oceans GREEN!

Evidence for the Evolution of an Oxygen Rich Atmosphere: Banded Iron Formations

• Sedimentary rocks consisting of layers of cherts (SiO2) and iron oxides/sulfides

Very Extensive deposits--100’s of meters thick, 100’s of km in extent. Formed when Fe+2 (Ferrous - soluble in water) comes in contact with O2 forming insoluble (Ferric) Fe+3

• Common from 2.5-2.0 BY

BIFs and the Proterozoic Atmosphere • Fe2+ (reduced Fe)

dissolves easily in the ocean. Seawater also contains dissolved Si

• Photosynthesizing cyanobacteria produce O2.

• Oxidized Fe to FE3+ and Fe4+ which precipitate as magnetitie and hematite along with chert (SiO2).

• When Fe2+ exhausted, massive BIFs ceased to form.