EARTH’S ORIGIN AND MATERIALS
Earth as viewed from space
All constructions are affected by the earth, and thus require some geological knowledge
Energy and mineral resources that we depend on for our lifestyle come from the Earth
Why?
Chapter 2
Mercury
Venus
Earth
Mars
Jupiter
Saturn
Uranus
Neptune
Earth is one of nine planetary bodies that revolve around the sun There are two groups of planets: Four smaller planets close to sun, dense bodies mainly composed of
iron and silicate rocks Four giant planets far form sun, much lighter in density because of
their gaseous composition
History of solar system Big Bang Theory 15 billion years ago Expansion of the universe from a single point
10 billion years after Big Bang
o Dust Cloud : a large diffuse gas and dust slowly rotated in space “ solar nebula” o The “solar nebula” began to contract due to gravitational forces o A concentration of matter formed at its center, its temperature raised
causing a nuclear fusion SUN o The sun is composed of 99% hydrogen and helium
o The matter rotating around the newly formed sun gradually cooled and condensed into the nine planets
Earth ~4.5-4.56 billion years old.
Earth was originally hot, barren, and rocky with no liquid water
Only a very thin hydrogen/helium atmosphere.
Earth-Early Stages
Earth early stages
During formation, Earth became quite hot and partially molten. This allowed material segregation within the Earth according to its density. Dense material (iron, nickel) fell to the center of the Earth; lighter material rose to the surface
This phase lasted about 100-200 million years. Differentiation would have been mostly complete by this time unless that the “big splat “ occurred.
Giant Impact “The Big Splat'‘ : Very early in the Earth’s life, a body from 1-3 times the size of Mars, slammed into it.
The impact blasted a large part of Earth into space; this vaporized rock then began orbiting Earth.
The debris then began to coalesce into what became the “Moon”.
That impact melted again much of the earth, and allowed further differentiation to take place, so that by about 4.2 billion years ago differentiation would have been complete.
This is one explanation for why the Moon has so little iron: most of the Earth's iron was already near the center and was not blasted
Earth Differentiation
As Earth cooled, some of the water vapor in the atmosphere began
to condense and rain out onto the surface. Earth at this point would
have been a pretty good sauna - very hot and humid.
As more water rained out, the carbon dioxide in the atmosphere
began to dissolve into the water, which of course would have
reduced the amount in the atmosphere. Carbon dioxide is a so-called
“greenhouse'' gas; if you have too much of it in the atmosphere, the
temperature rise. Conversely, if you extract CO2 from the
atmosphere the surface temperature will drop.
Reduced temperature meant more rain so there would be more
liquid water, removing more CO2, making the temperature drop
more, making more rain, and so on. A Balance would have been
reached eventually.
away into space.
As Earth differentiated and cooled, gases and water vapor were released from the interior of the solid Earth and began to form an atmosphere. The early atmosphere was largely water vapor, nitrogen, methane, ammonia, and carbon dioxide, with very little free oxygen
Moon
The Earth System Components
Size: Radius about 6500 km
Atmosphere: gaseous envelope extending from the surface to about 1000 km
Hydrosphere: water in all rivers, lakes, oceans, and groundwater
Biosphere: organic matter related to life near the Earth’s surface
Lithosphere: strong, rocky outer shell of the solid Earth including all the crust to a depth of ~100 km
crust: Upper lithosphere;
Asthenosphere: weak, ductile layer of the mantle beneath the lithosphere;
Mantle: mantle beneath the asthenosphere (~400 to 2900 km in depth)
core: is 3500 km thick; Very hot, dense metallic material (Iron, Nickel, ...);
Outer core: is molten and generates the Earth's magnetic field with its currents convection.
Inner core: is the innermost sphere(10%) composed primarily of solid iron
Immobility is only apparent
Crust is dynamic :
continents shift position
mountains rise
erosion: cutting of valleys/mountains
earthquakes
volcanoes
crust thickness (km)
6-8 km oceans (oceanic crust)
70-80 km mountains (continental crust)
crust: broken-moves riding on the plastic upper portion of the mantle. energy from convection within mantle
Is the Earth Solid?
Mantle Convection
Convection
On the stove In the mantle
GEOLOGIC TIME
Geologist have subdivided the age of the earth (~4.6 billion years) into Eons, Eras, and Periods. These divisions are based upon major trends in the evolution of life on earth according to fossil records. In particular, the boundaries between the geologic eras represent times where mass extinctions have occurred:
Phanerozoic means visible life (Greek origin).
Cenozoic means recent life, also called the "Age of the Mammals".
Mesozoic means middle life, also called the "Age of the Reptiles" or "Age of the Dinosaurs".
Paleozoic means ancient life, also called the "Age of the Fish".
o Just because the Paleozoic era is called the age of the fish doesn't
mean there were no fish in the Mesozoic era.
How to Determine the Age of a Rock?
Relative dating - Steno's Laws
"A is older than B"
Absolute dating
Quantify the date in years. Radiometric Dating
Principles of Radiometric Dating
Naturally-occurring radioactive materials break down into other
materials at known rates. This is known as radioactive decay.
Radioactive parent elements decay to stable daughter
elements.
Radioactivity was discovered in 1896 by Henri Becquerel. In
1905, Rutherford and Boltwood used the principle of radioactive
decay to measure the age of rocks and minerals (using Uranium
decay).
Many radioactive elements can be used as geologic clocks. Each
radioactive element decays at its own nearly constant rate.
Once this rate is known, geologists can estimate the length of
time over which decay has been occurring by measuring the
amount of radioactive parent element and the amount of stable
daughter elements.
For example, if there are equal amounts of parent and daughter, then one half-life has passed.
If there is three times as much daughter as parent, then two half-lives have passed.
