Chapter 1
Earth Science
Course: Elementary Education Multiple Subjects 5001
Subject: Elementary Education Science Subtest 5005
Chapter: Earth Science
1. Origin and Early Evolution of Earth
a. Formation of Earth (~4.6 billion years ago)
Earth formed from the solar nebula—a rotating cloud of gas and dust left over after the Sun’s formation. As gravity pulled particles together, planetesimals formed. These collided and merged into a proto-Earth. Due to heat from impacts, radioactive decay, and compression, the early Earth was molten.
As the planet cooled, planetary differentiation occurred. Denser elements like iron and nickel sank toward the center to form the core, while lighter silicates formed the mantle and crust. This created Earth's layered internal structure: core, mantle, and crust.
b. Formation of the Moon
The most accepted theory—the giant impact hypothesis—proposes that a Mars-sized body (Theia) collided with early Earth. The impact ejected debris, which later coalesced to form the Moon. Supporting evidence includes: