The letters following each Review Question refer to the corresponding Learning Objective from the Chapter Opener. Describe the formation of the crust, atmosphere, and oceans during the Hadean Eon. (B)

The Hadean Eon marked the dawn of our planet's history, when the Earth's crust first began to form. During this chaotic period, the process called differentiation was at the forefront. This process separated the Earth into layers based on the density of elements. The heavier elements, like iron and nickel, sank towards the center, forming the core, while lighter elements such as silicon and aluminum rose to create the crust and mantle. The cooling of the Earth allowed the molten material in the mantle to crystallize, forming the primary basaltic crust.
As the Earth's surface cooled further, volcanic activity continued to shape the emerging crust, spewing forth more material that gradually solidified on the surface. The crust at this stage was thin and continuously disrupted by volcanic eruptions and the frequent meteorite impacts that marked this eon. Despite the tumultuous conditions, the foundations for present-day continents were being laid during this pivotal time.

The Earth's early atmosphere was a volatile concoction, distinctly different from the breathable air we are accustomed to today. With no free oxygen, the primordial atmosphere was filled with gases like hydrogen, methane, and ammonia—products of volcanic outgassing and leftover elements from the planet's initial formation. These gases created a thick, hot covering around the young Earth.
Over time, the surface of the planet began to cool, and the atmosphere saw dramatic changes. Water vapor, abundant in the early atmosphere, started to condense. This condensation led to rain, which would eventually become a pivotal player in the formation of the oceans. This period set the scene for the incredible changes that would sculpt our planet's air into the life-supporting system we know today.

As the post-impact heat dissipated and the Earth's early atmosphere stabilized, water vapor condensed and fell as rain, a process that may have lasted millions of years. This relentless precipitation collected in low-lying areas, birthing the first oceans. These oceans were likely very shallow initially, but as more water vapor cooled and precipitated, they deepened and expanded to form larger bodies.
These early oceans were warmer and likely more acidic than today's oceans, rich with minerals from volcanic activity and containing a mix of chemicals critical to forming the building blocks of life. As such, Earth's oceans became the cradle for the complex processes that would eventually lead to the emergence of life.

Meteorite bombardment played a dual role in Earth's early history. Not only did it deliver additional materials essential for the composition of the crust, but the energy released during impacts also generated significant heat. This heat was so intense that it caused the surface rock to melt and mix with the incoming extraterrestrial material.
The continual barrage reshaped the planetary surface, creating and destroying landforms. These meteoritic impacts contributed to the planet's geological diversity and played a part in the complex evolution of the Earth's crust. The period of heavy bombardment is a testament to the violent origins of our planet and its dynamic developmental journey.

Differentiation is the pivotal process through which the Earth stratified into layers. As the planet formed, gravitational forces pulled denser elements toward the center, creating the iron-rich core. Conversely, lighter elements floated upwards, eventually cooling to form the silicate mantle and crust.
This process is fundamental to understanding the structure of our planet. It not only shaped the physical layers but also set the stage for the tectonic activity that would drive the continual renewal and recycling of the Earth's crust. Differentiation is responsible for giving Earth its magnetic field, due to the movement of molten iron in the outer core, which is vital for protecting the planet from solar and cosmic radiation.