Chapter 2 – The Origin and Evolution of the Earth
What is the Big Bang Theory?
It explains the origin of the universe. Around 13.7 billion years ago, a massive explosion led to the expansion and formation of galaxies and celestial bodies.
What is the Solar System?
The Solar System includes the Sun and eight planets, their moons, asteroids, comets, and other celestial bodies.
How old is the Solar System?
It is approximately 4.6 billion years old, formed from a rotating cloud of gas and dust.
What is a nebula?
A nebula is a huge cloud of gas and dust in space, considered the birthplace of stars and planets.
What is the Nebular Hypothesis?
Proposed by Kant and Laplace, it suggests the Sun and planets formed from a rotating nebula that contracted under gravity.
What are planetesimals?
They are small solid objects in space that collided and combined to form planets during the early Solar System formation.
How did Earth form?
Earth formed through the accumulation of planetesimals and gas, followed by internal differentiation and cooling.
What are terrestrial planets?
Mercury, Venus, Earth, and Mars—rocky planets close to the Sun with solid surfaces.
What are Jovian planets?
Jupiter, Saturn, Uranus, and Neptune—gas giants, located farther from the Sun, with thick atmospheres and many moons.
What caused Earth’s interior to differentiate?
Radioactive decay and collisions caused heat, melting materials; heavier elements like iron sank to the core, while lighter ones rose.
What are the three layers of Earth’s interior?
Crust (outer layer), mantle (middle layer), and core (inner, mostly iron and nickel).
What is the age of Earth?
Approximately 4.6 billion years, similar to the age of the Solar System.
What is a supernova?
A massive explosion of a star at the end of its life, dispersing elements that contribute to new star systems.
What are meteors and asteroids?
Meteors are space rocks that burn in Earth’s atmosphere; asteroids are rocky bodies mostly found in the asteroid belt.
How did water come to Earth?
Water vapor from volcanic eruptions condensed into clouds and fell as rain, forming rivers, lakes, and oceans.
What is outgassing?
The release of gases like water vapor, carbon dioxide, and nitrogen from Earth’s interior through volcanic activity.
When did life begin on Earth?
Around 3.8 billion years ago, in the form of simple microscopic organisms in the oceans.
What is the primitive atmosphere?
Earth’s early atmosphere had no oxygen—only gases like methane, ammonia, and water vapor, formed by volcanic emissions.
What caused the formation of the ozone layer?
Oxygen released by photosynthetic organisms formed ozone (O₃), which protected life from harmful UV rays.
What is the significance of the ozone layer?
It absorbs harmful ultraviolet radiation, making Earth suitable for life to evolve on land.
What role did comets play in Earth’s evolution?
Comets possibly brought water and organic molecules, contributing to the formation of oceans and life.
What is the geological time scale?
It’s a timeline that organizes Earth’s history into eons, eras, periods, and epochs based on major events and fossil records.
What was the Hadean era?
The earliest eon in Earth’s history, marked by intense heat, volcanic activity, and the formation of the crust.
How was the Moon formed?
The Giant Impact Theory says a Mars-sized body collided with Earth, and the ejected material formed the Moon.
What gases dominated Earth’s early atmosphere?
Mainly carbon dioxide, water vapor, methane, ammonia—no free oxygen existed initially.
What is the role of cyanobacteria in evolution?
They were the first organisms to perform photosynthesis, releasing oxygen into the atmosphere, essential for higher life forms.
What were the first forms of life?
Single-celled prokaryotes in oceans, such as archaea and bacteria, emerged nearly 3.8 billion years ago.
Why is Earth called a unique planet?
Because it has water, atmosphere, suitable temperature, and conditions to support life.
What is accretion in planetary formation?
It’s the process by which small particles collide and stick together to form larger bodies like planetesimals and planets.
What is the significance of this chapter?
It explains how the universe, Solar System, Earth, and life began—laying the foundation for physical geography.