Geology: Chapter 1 - The Earth System

Thickness of continental crust

40 km

Thickness of oceanic crust

7-8 km

Which elements account for 90% of the Earth's mass?

90%: iron, oxygen, silicon, and magnesium Iron is concentrated in the core while oxygen is concentrated in the crust/mantle --> these varying compositions based on depths are due to gravity

Geology

A branch of Earth Science (a planetary science) that studies all aspects of the planet: its history, its composition / internal structure, and its surface features --> studies both the extreme geological events and the gradual ones

Theory

A coherent set of hypotheses that explains some aspect of nature

Seismic waves

A ground vibration produced by an earthquake. Come in two forms: compressional waves (expand/compress material they move through) and shear waves (move the material side to side - only goes through solids)

Biosphere

All organic matter related to life near Earth's surface

Geodesy

An old branch of Earth science that studies Earth's shape and surface

When was the Earth formed?

Approximately 4.56 billion years ago through the rapid condensation of a dust cloud that circulated around the young sun. Oldest rocks found on Earth are over 4 billion years old. Rocks that are 3.5 billion years old show evidence of a magnetic field. 2.7 billion years ago saw a rising oxygen content of the atmosphere due to its production by organisms. 600 million years ago animals appeared. Homo sapiens only appeared 200,000 years ago.

How did scientists discover the layering of the Earth?

At the end of the 19th center, the first network of seismographs was installed which allowed geologists to discover the concentric layers of different compositions at Earth's interior

Discovery of the Core

Croatian scientist discovered boundary at depth of 40 km which separated the crust (composed of low-density silicates - rich in aluminum/potassium) form the higher density silicates of the mantle (rich in magnesium and iron)

Why do plates move across Earth's surface instead of locking up into a completely rigid shell?

Driven by the Earth's internal heat engine, hot mantle material rises at boundaries where plates separate, forming new lithosphere. The lithosphere cools and becomes more rigid as it moves away from these boundaries, eventually sinking back into the mantle under the pull of gravity at boundaries where plates converge. This general process is called convection (hotter material rises, cooler material sinks)

climate system

Earth system components that determine climate on a global scale and how climate changes with time. Involves interactions with the atmosphere, hydrosphere, biosphere, cryosphere, and lithosphere and is energized by solar radiation

Mantle and Core Discovery

Emil Wiechert postulated that the iron and nickel in Earth's interior had dropped inward under the force of gravity, creating a dense core surrounded by a mantle, or shell of silicate-rich rock. In 1906, Robert Oldham discovered that shear waves did not propagate through the Earth's core, meaning that at least in its outer part it was liquid

Atmosphere

Gaseous envelope extending from the Earth's surface to an altitude of about 100 km

Who was Emil Wiechert?

He was the first to propose the idea of layering of Earth's interior. He wanted to understand why our planet was so dense --> if it was just made of rocks it shouldn't have been that dense. Even if the increased pressure on the rocks deeper down attributed to the higher density, it was not enough to account for it entirely. Also postulated that the iron and nickel in Earth's interior had dropped inward under the force of gravity, creating a dense core surrounded by a mantle, or shell of silicate-rich rock

Which elements are rich in the mantle?

High-density silicates rich in magnesium and iron

What was interesting about Earth's density prior to the discovery of its core?

If it was just made of rocks it shouldn't have been as dense as Henry Cavendish calculated. Even if the increased pressure on the rocks deeper down attributed to the higher density, it was not enough to account for it entirely

Plate tectonic system

Involves interactions among the lithosphere, asthenosphere, and deep mantel. Is energized by Earth's internal heat

Geodynamo systems

Involves interactions that produce a magnetic field deep inside Earth in its liquid other core. Based on interactions between the inner and outer cores and is energized by Earth's internal heat

Earth as an open system

It exchanges energy and mass with its surroundings. Randiant energy from the Sun energizes the weathering/erosion of the Earth's reface and the growth of plants, while Earth's climate is controlled by the balance between solar energy coming into the Earth system and the what energy Earth radiates back into space

Where does Earth's 'internal heat engine' originate from?

It is powered by the heat energy trapped in its deep interior and released inside the planet by radioactivity --> this drives movement in the mantle/core, supplying the energy that melts rock, moves continents, lifts up mountains

Where does Earth's 'external heat engine' originate from?

It is supplied by the heat from the Sun --> this energizes the atmosphere/oceans and is responsible for the Earth's climate and weather

Which elements are rich in the crust?

Low-density silicates rich in aluminum and potassium

Deep Mantle

Mantle beneath the asthenosphere, extending from about 400 km deep to the core-mantle boundary

Principle of uniformitarianism

Notion that the processes we see in action on Earth today have worked in much the same way throughout the geologic past --> present is the key to the past

Cryosphere

Polar ice caps, glaciers, and other surface ice and snow

Are rocks in the oceanic or continental crust denser?

Rocks in the oceanic crust are denser as they contain more iron, but they are less thick. Since the continents are less dense then the mantle they ride higher as they float

Sea level

Smooth surface set at the average level of ocean water that conforms closely to the squashed, spherical shape expected for the rotating Earth

Geosystem

Specialized subsystem that produces specific types of activity, such as climate change or mountain building ->Earth = collection of many open, interacting geosystems

Lithosphere

Strong, rocky outer shell of the solid Earth that comprises the crust and uppermost mantle to an average depth of about 100 km; forms the tectonic plates. These plates ride on the asthenosphere

Hydrosphere

Surface waters comprising all oceans, lakes, rivers, and groundwaters

Inner core

The central part of Earth below a depth of 5150 km, consisting of a solid sphere (can transmit shear & compressional waves), composed of iron and nickel, suspended within the liquid outer core. Radius of 1220 km = 2/3 size of the Moon. The 'freezing' of the inner core is due to the higher pressures (despite such high temperatures)

Core

The dense central part of Earth below the core-mantle boundary, composed principally of iron and nickel

Topography

The general configuration of varying heights that gives shape to Earth's surface, which is measured with respect to sea level

Scientific method

The general procedure used by scientists for discovering how the universe works through systematic observations and experiments

Geologic record

The information preserved in rocks that have been formed at various times throughout Earth's history

Outer core

The layer of Earth extending from the core-mantle boundary to the inner core, at depths of 2890 to 5150 km, composed of molten iron and nickel and minor amounts of lighter elements such as oxygen or sulfur. Since it is liquid, it reflects seismic waves

Mantle

The region that forms the main bulk of Earth between the crust and the core, containing rocks of intermediate density, mostly compounds of oxygen with magnesium, iron, and silicon. Consists of the upper and lower mantle which is separated by a transition zone where the rock density increases in a series of steps due to increasing pressure with depth

Crust

The thin outer layer of Earth, averaging from about 8 km thick under the oceans to about 40 km thick under the continents, consisting of relatively low-density silicates (rich in aluminum/potassium) that melt at relatively low temperatures

Asthenosphere

Weak, ductile layer of mantle beneath the lithosphere that deforms to accommodate the horizontal and vertical motions of plate tectonics

Seismic topography

a technique that uses differences in the travel times of seismic waves produced by earthquakes and recorded by seismographs to construct three-dimensional images of the Earth's interior

Fossils

traces of organisms preserved in the geologic record