The Whole History of the Earth and Life 　Part2:Initiation of Plate Tectonics(2nd edition)

Summary

The early Earth, bombarded by planetesimals and icy planets, formed an atmosphere and ocean over 200 million years. Initially toxic, the ocean's high salinity and heavy metals prevented life. Asteroid impacts created magma and basaltic crust, leading to oceanic and continental crust development through plate tectonics. Subduction neutralized the acidic ocean, fixing heavy metals as deposits. A liquid core formed, generating a magnetic field that protected Earth from solar winds and cosmic rays, making it ready for life.

Takeaways

• 🌍 The early Earth lacked an atmosphere and an ocean.
• ☄️ Planetesimals and icy planets bombarded Earth for 200 million years.
• 🧬 An ocean-atmosphere system began forming from elements in planetesimals.
• 🌊 The early ocean was toxic with high salinity and heavy metals, making it uninhabitable.
• 💥 Asteroids 1,000 kilometers in diameter impacted Earth, turning crust and asteroids into plasma.
• 🗻 Basaltic crust formed from cooling magma, creating oceanic crust thinner than continental crust.
• 🌧 Surface water pooled in craters, forming the early ocean.
• 🌋 Mantle convection caused breaches in the oceanic crust, leading to plate tectonics.
• 🌎 Oceanic plates subducted under continental plates, neutralizing the acidic ocean.
• 🌡 Heavy metals settled and became deposits, making the ocean habitable over time.
• 🔥 A liquid core formed in Earth's center 4.2 billion years ago, creating a geomagnetic field.
• 🛡 The geomagnetic field protects Earth from solar winds and cosmic rays, preparing it for life.

Q & A

What were the conditions of the early Earth?

The early Earth had neither an atmosphere nor an ocean and was bombarded by countless planetesimals and icy planets over a period of 200 million years.

How did the ocean and atmosphere system form on early Earth?

The ocean and atmosphere system formed from carbon, hydrogen, oxygen, and nitrogen contained in planetesimals that bombarded the Earth.

What were the characteristics of the early ocean?

The early ocean was toxic, with high salinity and an overabundance of heavy metals, making it too toxic to support life.

What happened when asteroids with a diameter of 1,000 kilometers hit the Earth?

When these large asteroids impacted Earth, both the crust and asteroids became plasma, and the surface was covered with magma. A basaltic central cone formed in the center of the crater, creating an upflow in the mantle.

What is oceanic crust and how did it form?

Oceanic crust is thinner than continental crust and formed when magma cooled and solidified after asteroid impacts.

How did the early oceans form?

Surface water flowed into giant craters, forming small puddles that eventually combined into one large ocean.

What role did mantle convection play in plate tectonics?

Mantle convection caused uplift of the plate, leading to horizontal slippage due to the weight of the plate, which is plate tectonics in action.

How were the ultra-acidic oceans neutralized?

Weathered sediments neutralized the ultra-acidic oceans, and heavy metals settled out and became fixed as deposits at the mid-oceanic ridge.

How did the ocean become a habitable environment?

As heavy metals settled out and were transported into the deep mantle through plate tectonics, the ocean gradually became a habitable environment.

What is the significance of the Earth's liquid core and its convection?

The liquid core, which formed 4.2 billion years ago, creates a strong magnetic field through convection. This geomagnetic field shields the Earth's surface from solar winds and cosmic rays, making it more suitable for life.