Explore 3.18 Forming Earth and Its Component Systems
Learning Objectives
By the time you have completed the 3.18. Introduction & Exploration Activities, you should be able to:
Understand the meaning of the following terms/concepts and be able to identify examples of each: accretion, differentiation, meteorite, undifferentiated meteorite, differentiated meteorite, iron meteorite, stony meteorite, stony-iron meteorite, the Moon, Earth’s crust, Earth’s mantle, Earth’s core, Earth’s magnetic field, rocky Earth (mantle & crust), Earth’s hydrosphere/atmosphere, Earth’s biosphere.
Describe how differentiation produced Earth’s layers (core, mantle, and crust).
Understand the role of planetary differentiation in producing the component systems of Earth’s habitability (magnetosphere, rocky Earth, hydrosphere, atmosphere, & biosphere). Also, describe the role of each component system in making Earth habitable (for example, Earth’s core produces a magnetic field that protects life from harmful solar radiation)
Answer: Accretion is the incremental growth process that produces planetary bodies by collision of orbiting solids. Through accretion, dust in our proplyd formed pebbles, rocks, boulders, and eventually asteroids, planets and comets.
Accretion is the incremental growth process that produces planetary bodies by collision of orbiting solids. Through accretion, dust in our proplyd formed pebbles, rocks, boulders, and eventually asteroids, planets and comets.
Example:
Answer: As you can see in this image, there is a lot of material moving around in our solar system during its formation. As the material collides with other material, accretion takes place. The material combines to form larger rock bodies. Eventually planets form.
As you can see in this image, there is a lot of material moving around in our solar system during its formation. As the material collides with other material, accretion takes place. The material combines to form larger rock bodies. Eventually planets form.
Term:
Differentiation
Definition:
Answer: Differentiation is the process of separating planetary materials by density.
Differentiation is the process of separating planetary materials by density.
Example:
Answer: Differentiation is essentially the ‘unmixing’ of materials after accretion has occurred. As you can see in this image, the differentiation led to layers in the Earth.
Differentiation is essentially the ‘unmixing’ of materials after accretion has occurred. As you can see in this image, the differentiation led to layers in the Earth.
Term:
Meteorite
Definition:
Answer: Rocks from the asteroid belt (and less commonly from other bodies like the Moon and Mars) sometimes collide with Earth. We call these rocks meteorites.
Rocks from the asteroid belt (and less commonly from other bodies like the Moon and Mars) sometimes collide with Earth. We call these rocks meteorites.
Example:
Answer: One of the most famous meteorites is the Allende Meteorite, which fell in Mexico in 1969.
One of the most famous meteorites is the Allende Meteorite, which fell in Mexico in 1969.
Term:
Undifferentiated Meteorite
Definition:
Answer: Undifferentiated meteorites are space rocks composed of primitive solids that formed in the early Solar System. They consist of finely intermixed rock and metal.
Undifferentiated meteorites are space rocks composed of primitive solids that formed in the early Solar System. They consist of finely intermixed rock and metal.
Example:
Answer: The image you see here was in our reading. This is an example of an undifferentiated meteorite (carbonaceous chondrite).
The image you see here was in our reading. This is an example of an undifferentiated meteorite (carbonaceous chondrite).
Term:
Differentiated Meteorite
Definition:
Answer:Differentiated meteorites are space rocks that formed as part of the crust, mantle or core of a planetary body.
Differentiated meteorites are space rocks that formed as part of the crust, mantle or core of a planetary body.
Example:
Answer: These images of meteorites from your reading represent differentiated meteorites.
These images of meteorites from your reading represent differentiated meteorites.
Term:
Iron Meteorite
Definition:
Answer: Iron meteorites are differentiated meteorites that originated in a core.
Iron meteorites are differentiated meteorites that originated in a core.
Example:
Answer: This image is of an iron meteorite.
This image is of an iron meteorite.
Term:
Stony Meteorite
Definition:
Answer: Stony meteorites are those that formed at the mantle or crust.
Stony meteorites are those that formed at the mantle or crust.
Example:
Answer: This image is a eucrite, from the crust of the second largest asteroid, Vesta.
This image is a eucrite, from the crust of the second largest asteroid, Vesta.
Term:
Stony-iron Meteorite
Definition:
Answer: Stony-iron meteorites are those that formed at a core-mantle boundary.
Stony-iron meteorites are those that formed at a core-mantle boundary.
Example:
Answer: This image is a a stony-iron meteorite (a pallasite)
This image is a a stony-iron meteorite (a pallasite)
Term:
Moon
Definition:
Answer: A moon is an airless, geologically dead planetary body.
A moon is an airless, geologically dead planetary body.
Example:
Answer: Our moon orbits Earth like a natural satellite. The moon helps stabilize Earth’s tilt.
Our moon orbits Earth like a natural satellite. The moon helps stabilize Earth’s tilt.
Term:
Earth’s Crust
Definition:
Answer: Earth’s crust is the outermost layer of Earth. It is made of solid rock. It makes up less than 1% of Earth’s volume.
Earth’s crust is the outermost layer of Earth. It is made of solid rock. It makes up less than 1% of Earth’s volume.
Example:
Answer: Crystal rock is less dense than mantle rock, which is why the crust forms our planet’s surface. As you can see in this image, there is crust above and below water on our planet.
Crystal rock is less dense than mantle rock, which is why the crust forms our planet’s surface.
As you can see in this image, there is crust above and below water on our planet.
Term:
Earth’s Mantle
Definition:
Answer: Earth’s mantle is the layer of earth just below the Earth’s crust. Like the crust, it is made of solid rock. It makes up about 84% of Earth’s volume.
Earth’s mantle is the layer of earth just below the Earth’s crust. Like the crust, it is made of solid rock. It makes up about 84% of Earth’s volume.
Example:
Answer: Convection currents that run through the Earth’s mantle drive plate tectonic movement. The lithosphere shown in this image represents the crust and the top most layer of the mantle.
Convection currents that run through the Earth’s mantle drive plate tectonic movement. The lithosphere shown in this image represents the crust and the top most layer of the mantle.
Term:
Earth’s Core
Definition:
Answer: Earth’s core represents the center of Earth. Earth’s core consists mostly of iron & nickel—with a few percent of light elements like silicon, carbon, & sulfur and small amounts of other metals like platinum and gold.
Earth’s core represents the center of Earth. Earth’s core consists mostly of iron & nickel—with a few percent of light elements like silicon, carbon, & sulfur and small amounts of other metals like platinum and gold.
Example:
Answer: Earth’s core makes up more than half of its radius and consists of a solid inner sphere surrounded by a thick layer of molten metal.
Earth’s core makes up more than half of its radius and consists of a solid inner sphere surrounded by a thick layer of molten metal.
Term:
Earth’s Magnetic Field
Definition:
Answer: The inner core, convection in the outer core and Earth’s rotation combine to produce a magnetic field that envelops Earth and nearby space.
The inner core, convection in the outer core and Earth’s rotation combine to produce a magnetic field that envelops Earth and nearby space.
Example:
Answer: Earth’s magnetic field protects Earth from solar radiation that would otherwise strip away Earth’s atmosphere and make Earth’s surface uninhabitable.
Earth’s magnetic field protects Earth from solar radiation that would otherwise strip away Earth’s atmosphere and make Earth’s surface uninhabitable.
Term:
Rocky Earth (Mantle & Crust)
Definition:
Answer:Earth’s rocky crust and mantle form rocky Earth.
Earth’s rocky crust and mantle form rocky Earth.
Example:
Answer: Rocky Earth is Earth’s system responsible for the tectonic activity we discussed earlier in this unit. Remember that some planets are rocky and others are comprised primarily of gasses.
Rocky Earth is Earth’s system responsible for the tectonic activity we discussed earlier in this unit. Remember that some planets are rocky and others are comprised primarily of gasses.
Term:
Earth’s Hydrosphere/Atmosphere
Definition:
Answer: The hydrosphere and atmosphere consists of Earth’s least dense, outermost material layers.
The hydrosphere and atmosphere consists of Earth’s least dense, outermost material layers.
Example:
Answer: The hydrosphere makes up all of the water on earth. The atmosphere is the gas that surrounds our planet.
The hydrosphere makes up all of the water on earth. The atmosphere is the gas that surrounds our planet.
Term:
Earth’s Biosphere
Definition:
Answer: Earth’s biosphere consists of all living things.
Earth’s biosphere consists of all living things.
Example:
Answer: The biosphere is where living organisms live. This could be on earth, air, or water.
The biosphere is where living organisms live. This could be on earth, air, or water.
Differentiation Produces Layers
Sometimes when we think of differentiation, we think of this:
But differentiation is the process of separating planetary materials by density. This density separation or ‘unmixing’ produces layered planetary bodies with metallic cores surrounded by rocky mantles and crusts - as was mentioned in our reading.
When Earth first formed, it looked more similar to our moon. What caused the differentiation in the layers of the earth?
Answer: Heat increased on our planet as our planet experienced radioactive decay (as mentioned in our previous lesson). Heat also increased on our planet from accretionary collisions from meteorites. We will discuss meteorites more in the next section. These activities,combined with gravity, pulled the heavier materials like nickel and iron, to the core of the earth, leaving the lighter materials closer to the surface.
Heat increased on our planet as our planet experienced radioactive decay (as mentioned in our previous lesson). Heat also increased on our planet from accretionary collisions from meteorites. We will discuss meteorites more in the next section. These activities,combined with gravity, pulled the heavier materials like nickel and iron, to the core of the earth, leaving the lighter materials closer to the surface.
Watch this video (about 5 minutes) to review the formation of the solar system (including Earth).
Understand the role of planetary differentiation in producing the component systems of Earth’s habitability (magnetosphere, rocky Earth, hydrosphere, atmosphere, & biosphere). Also, describe the role of each component system in making Earth habitable (for example, Earth’s core produces a magnetic field that protects life from harmful solar radiation)
Meteorites are invaluable records of the nature and development of the early Solar System. The following questions will help to deepen our understanding of planetary differentiation, which produced the interacting systems that make Earth habitable.
What is the role of planetary differentiation in producing the magnetosphere?
Answer: Earth’s spin and the flow of liquid iron in Earth’s outer core generate a magnetic field that mostly prevents the solar wind from encountering Earth’s atmosphere. We say mostly because unusually strong pulses of solar wind do penetrate Earth’s upper atmosphere… and produce the aurora.
Earth’s spin and the flow of liquid iron in Earth’s outer core generate a magnetic field that mostly prevents the solar wind from encountering Earth’s atmosphere. We say mostly because unusually strong pulses of solar wind do penetrate Earth’s upper atmosphere… and produce the aurora.
What caused Earth to differentiate?
Answer: Heat from accretion (collisions) and radioactive decay caused Earth to differentiate. Accretion produced Earth, and differentiation was the first major planetary process to occur on Earth. Evidence recorded in Earth materials indicate that Earth’s Moon, core, and atmosphere formed no later than 30 My after accretion produced Earth. These early years were chaotic! Research performed by Dr. Tonks has shown that the large meteorite impacts that characterized the accretion process would have triggered core formation by the time Earth was Mars-sized, when Earth contained just 10% its present matter. After initial differentiation, the process of differentiation would have continued as Earth grew. Earth’s earliest atmosphere likely formed from the gases adsorbed on and ‘dissolved’ in the solid materials that collided to form our planet. This atmosphere likely contained abundant carbon dioxide, nitrogen, methane, sulfur dioxide, and so forth.
Heat from accretion (collisions) and radioactive decay caused Earth to differentiate.
Accretion produced Earth, and differentiation was the first major planetary process to occur on Earth. Evidence recorded in Earth materials indicate that Earth’s Moon, core, and atmosphere formed no later than 30 My after accretion produced Earth. These early years were chaotic! Research performed by Dr. Tonks has shown that the large meteorite impacts that characterized the accretion process would have triggered core formation by the time Earth was Mars-sized, when Earth contained just 10% its present matter. After initial differentiation, the process of differentiation would have continued as Earth grew. Earth’s earliest atmosphere likely formed from the gases adsorbed on and ‘dissolved’ in the solid materials that collided to form our planet. This atmosphere likely contained abundant carbon dioxide, nitrogen, methane, sulfur dioxide, and so forth.
Briefly describe the event that formed the Moon.
Answer: The Moon formed from debris produced when another planet collided with Earth. This colossal event, which likely occurred quite late in Earth’s accretion, re-forged much of the Earth. Although evidence is unable to falsify the giant impact origin for the Moon, that same evidence struggles to differentiate between specific aspects of the Moon’s formation. For example, was the Moon the result of a glancing blow by a single large protoplanet (about the size of Mars)? Or did it result from multiple giant impacts with smaller protoplanets? Simulations of Moon-forming collisions show that most of the projectile(s) and the upper about 10% of Earth would have been vaporized. As this vapor expanded, a small fraction of it began orbiting Earth, cooled, and formed small solids that accreted to form the Moon. The collision(s) increased Earth’s internal temperature, which would have further differentiated Earth. In addition, the core(s) of the impactor(s) joined with Earth’s core.Also, the collision(s) reset the speed and orientation of Earth’s rotation (for example, its spin rate and tilt). The image below shows a still-accreting Moon orbiting Earth
The Moon formed from debris produced when another planet collided with Earth.
This colossal event, which likely occurred quite late in Earth’s accretion, re-forged much of the Earth. Although evidence is unable to falsify the giant impact origin for the Moon, that same evidence struggles to differentiate between specific aspects of the Moon’s formation. For example, was the Moon the result of a glancing blow by a single large protoplanet (about the size of Mars)? Or did it result from multiple giant impacts with smaller protoplanets? Simulations of Moon-forming collisions show that most of the projectile(s) and the upper about 10% of Earth would have been vaporized. As this vapor expanded, a small fraction of it began orbiting Earth, cooled, and formed small solids that accreted to form the Moon. The collision(s) increased Earth’s internal temperature, which would have further differentiated Earth. In addition, the core(s) of the impactor(s) joined with Earth’s core.Also, the collision(s) reset the speed and orientation of Earth’s rotation (for example, its spin rate and tilt). The image below shows a still-accreting Moon orbiting Earth
What is the age of the earliest evidence of liquid water on Earth’s surface?
Answer: The Moon-forming impact(s) completely destroyed Earth’s original atmosphere. Another aspect of Dr. Tonks’ research has shown that the impact(s) would have melted at least half of Earth, and perhaps more. Just as volcanoes release gases today from Earth’s interior, molten rock (magma) produced by collisions would have produced a new atmosphere for Earth, and subsequent volcanic activity and impacts by rocky and icy bodies would have continued adding gases to the post-impact atmosphere. As mentioned, Earth materials record that early Earth was hot. The first record of abundant glaciers on Earth is found in rocks formed at 2.7 Bya, some 1.8 Bya after its origin. However, at this time the Sun was about 30% less luminous (hot) than it is today, so it delivered less heat to Earth’s surface. The composition of Earth’s early atmosphere would have been similar to the current atmospheres of Venus or Mars, both of which consist of 96% CO2, 3% N2, and about 1% Ar. And the abundance of greenhouse gases (for example, CO2) in the early atmosphere would have kept early Earth hot, despite receiving less heat from the Sun. The hot early Earth lacked oceans but had abundant atmospheric water vapor. As Earth cooled, that water condensed, raining to Earth’s surface over a period of tens to hundreds of thousands of years—eventually forming the first oceans, which covered much of Earth.
The Moon-forming impact(s) completely destroyed Earth’s original atmosphere. Another aspect of Dr. Tonks’ research has shown that the impact(s) would have melted at least half of Earth, and perhaps more. Just as volcanoes release gases today from Earth’s interior, molten rock (magma) produced by collisions would have produced a new atmosphere for Earth, and subsequent volcanic activity and impacts by rocky and icy bodies would have continued adding gases to the post-impact atmosphere.
As mentioned, Earth materials record that early Earth was hot. The first record of abundant glaciers on Earth is found in rocks formed at 2.7 Bya, some 1.8 Bya after its origin. However, at this time the Sun was about 30% less luminous (hot) than it is today, so it delivered less heat to Earth’s surface. The composition of Earth’s early atmosphere would have been similar to the current atmospheres of Venus or Mars, both of which consist of 96% CO2, 3% N2, and about 1% Ar. And the abundance of greenhouse gases (for example, CO2) in the early atmosphere would have kept early Earth hot, despite receiving less heat from the Sun. The hot early Earth lacked oceans but had abundant atmospheric water vapor. As Earth cooled, that water condensed, raining to Earth’s surface over a period of tens to hundreds of thousands of years—eventually forming the first oceans, which covered much of Earth.
