4.2THE EARTH

TERRESTRIAL COMPOSITION The four terrestrial planets all

have similar internal features: Dense, metallic core Less dense, liquid-like mantle Low-density, solid crust

FOUR STAGES OF PLANETARY DEVELOPMENT

Earth is believed to have formed about 4.6 BYA from the solar nebula.

Along with the other terrestrial planets, Earth passed through 4 developmental stages:1. Differentiation

2. Cratering

3. Flooding

4. Slow Surface Evolution

FOUR STAGES OFPLANETARY DEVELOPMENT

Recall, differentiation, the separation of material according to density, is believed to have occurred due to melting of Earth’s interior. Heat generated from radioactive decay and energy

released from in-falling matter.

FOUR STAGES OFPLANETARY DEVELOPMENT

The heavy bombardment about occurred about 4 BYA and made craters on Earth and other planets.

When the environment cooled, water fell as rain and flooded the deep basins of Earth.

Continuing surface evolution over the past 3.5 billion years has constantly re-shaped the surface of the Earth (geologic processes along with weathering/erosion).

TECTONIC PLATES Earth’s crust is composed into several distinct pieces,

which are in constant motion with respect to each other and this process is known as plate tectonics.

Evidence of this is found on the ocean floor …

… and in geologically active regions across the Pacific.

TECTONIC PLATES Where plates move toward one another, they can be pushed

upward or downward convergent plate boundary. Formation of mountain ranges, presence of volcanic activity and/or

earthquakes.

Where plates move away from each other, magma can rise up, producing volcanism divergent plate boundary.

Hot spots result of magma penetration through holes in tectonic plates (Hawaii formation)

About 1 BYA, the supercontinent Rodinia, meaning “motherland”, existed. Most landmasses were gathered south of the equator.

THE SUPERCONTINENT CYCLE

About 450 MYA, after Rodinia broke up, Earth’s continents were separated as they are today.

THE SUPERCONTINENT CYCLE

The continents had joined back together around 200 MYA in the supercontinent Pangaea, meaning “all Earth”. Certain mountain ranges formed, including the Appalachians.

THE SUPERCONTINENT CYCLE

When Pangaea split apart, it eventually separated into a northern piece (Laurasia) and a southern piece (Gondwanaland) around 150 MYA.

THE SUPERCONTINENT CYCLE

About 50 MYA, the continents continued their separation, resembling their current-day locations. India collided with Eurasia Himalaya Mountain formation.

THE SUPERCONTINENT CYCLE

Believed if plate movements continue at current rates, in 150 million years, Africa will collide with Eurasia, closing off Mediterranean Sea. New subduction zones will form, closing off the Atlantic as well.

THE SUPERCONTINENT CYCLE

A new supercontinent, Pangaea Ultima, will form in approximately 250 million years.

THE SUPERCONTINENT CYCLE

HISTORY OF GEOLOGIC ACTIVITY

Surface formations visible today have emerged only very recently compared to the age of Earth.

EARTH’S INTERIOR High temperature and tremendous

pressure in Earth’s interior make any direct exploration impossible.

Exploration possible because earthquakes produce vibrations called seismic waves, traveling through the interior of the Earth.

Register on sensitive detectors called seismographs all over the world.

EARTH’S INTERIOR

Two main types of seismic waves: Body – seismic waves traveling through the body of

a medium (fastest-moving seismic wave category). P waves S waves

Surface – seismic waves traveling along the surface of a body rather than through the middle of it (slowest-moving seismic wave category; most destructive).

Rayleigh waves Love waves

P WAVES Body waves traveling through solids and liquids are called P

waves. “Primary” waves “Pressure” waves

Fastest moving seismic wave. Avg. speed in crust = 6.1 km/s

Particles of rock move in a back-and-forth direction.

P WAVES

S WAVES Body waves traveling through only solids are called S waves.

“Secondary” Waves “Shear” Waves

Second fastest seismic wave. Avg. speed in crust = 4.1 km/s

Particles of rock move in an side-to-side direction.

RAYLEIGH WAVES & LOVE WAVES

Rayleigh waves are surface waves causing the ground to move with an elliptical, rolling motion.

Love waves are surface waves causing the ground to move with a side to side motion perpendicular to the direction of the traveling wave.

SEISMOLOGY

The P and S waves (body) caused by an earthquake do not travel in straight lines or at constant speeds within the Earth.

May reflect off boundaries between the layers of different density, or they may be refracted as hey pass through a boundary.

Such information can be analyzed to infer the structure of Earth’s interior.

EARTH’S STRUCTURE

Earth’s interior gets hotter towards the center. Earth’s core is as hot as the Sun’s surface; metals are liquid.

Solid crust

Solid mantle

Liquid coreSolid inner core

Melting point = temperature at which an

element melts Melting point increases with

increasing pressure towards the center

- Reason inner core becomes solid

EARTH’S MAGNETIC FIELD

Earth’s core consists mainly of Iron (Fe) and Nickel (Ni) Both have high electrical

conductivity.

The rotation of the convecting, conducting liquid (outer core) generates Earth’s magnetic field in a process called the dynamo effect. Same process that generates

the solar magnetic field in the convective layers of the Sun.

EARTH’S MAGNETIC FIELD

Earth’s magnetic field protects it from the solar wind (ionized gases). The surface of the magnetic field where the

solar wind is first deflected is called the bow shock.

The region where Earth’s magnetic field dominates is called the magnetosphere.

High-energy particles from the solar wind leak into the magnetosphere and become trapped within Earth’s magnetic field and produce belts of radiation known as the Van Allen belts.

EARTH’S MAGNETIC FIELD

As high-energy particles leak into the lower magnetosphere, they excite molecules near

the Earth’s magnetic poles, causing the auroras.

EARTH’S ATMOSPHERE Earth once had a primeval atmosphere composed of

gases captured from the solar nebula during the formation of Earth (H, He, CH4).

Composition was severely altered, eventually led to a secondary atmosphere through 2 main processes:1. Outgassing: release of

gases in Earth’s interior through volcanism. During a volcanic eruption, 50-80% of the gas released is water vapor. The rest is CO2, nitrogen, and small amounts of sulfur gases.

2. Later bombardment with icy meteoroids and comets.

EARTH’S ATMOSPHERE

The ozone layer exists in the second layer of Earth’s atmosphere, the stratosphere. Composed of 3 oxygen atoms linked together, O3.

Absorbs (is opaque to) ultraviolet radiation from the Sun, protecting life on Earth’s surface.

GREENHOUSE EFFECT

Earth’s surface is heated by radiation from the Sun. Heat energy is re-radiated from

Earth’s surface as infrared radiation.

CO2 makes the atmosphere less transparent to infrared radiation (more opaque). Just as glass is opaque to

infrared radiation in a greenhouse.

Thus, heat is trapped due to CO2 through a process known as the greenhouse effect.

HUMAN EFFECTS The Greenhouse Effect occurs naturally an is essential

to maintain comfortable temperatures on Earth.

However, human activity may be increasing the concentration of greenhouse gases through CO2 emissions (cars and industrial plants) and deforestation through what is known as global warming.

HUMAN EFFECTS The amount of warming to

expect in the future is difficult to predict because Earth’s climate is critically sensitive to a number of different factors, not just the abundance of greenhouse gases.

For example, a planet’s albedo is the fraction of sunlight hitting it that gets reflected away. Albedo of 1 = WHITE Albedo of 0 = BLACK

Earth’s albedo is about 0.39 39% of sunlight hitting it reflects

back to space.

HUMAN EFFECTS Chlorofluorocarbons (CFC’s), used in

industrial processes, refrigeration, and air conditioning destroy the ozone layer (which absorbs UV radiation).

Destruction of the ozone layer proven ozone hole over Antarctica.