Origin of Life| Class 11 Geography Notes

Class 11 Geography Chapter 2: Origin of Life: The start of life from basic materials that weren’t alive is called the origin of life. When simpler life forms change and become more complex over time, it’s called the evolution of life. Life began on Earth around 3.5 to 4 billion years ago, and it’s been changing and growing ever since. In the beginning, all life was simple, just single cells. Later on, more complex creatures with many cells appeared, and this led to a huge variety of life on Earth.

In this article, we will delve deep into the topic of “Origin of Life” from Chapter 2 of the NCERT Class 12 Geography book. These notes are specially curated by an expert team at GeeksforGeeks for all the students.

Let’s get started!

Origin of Life

The final stage of Earth’s evolution involves the beginning and development of life. At first, Earth or its atmosphere wasn’t suitable for life to form. Scientists today believe life began through a chemical reaction. This reaction created complex organic molecules that could make copies of themselves, turning non-living stuff into living things. Evidence of life from different times is preserved in rocks as fossils. Microscopic structures similar to present-day blue-green algae have been found in rocks over 3 billion years old. It’s estimated life started evolving about 3.8 billion years ago. The Geological Time Scale summarizes life’s evolution from single-celled bacteria to modern humans.

Geological Time Scale Table

Era

Period	Epoch	Approximate Duration
Cenozoic	Quaternary	Holocene	11,700 years – Present
		Pleistocene	2.58 million – 11,700 years
	Tertiary	Pliocene	5.33 – 2.58 million years
		Miocene	23.03 – 5.33 million years
		Oligocene	33.9 – 23.03 million years
		Eocene	56 – 33.9 million years
		Paleocene	66 – 56 million years
Mesozoic	Cretaceous	Late Cretaceous	100.5 – 66 million years
		Early Cretaceous	145 – 100.5 million years
	Jurassic	Late Jurassic	163.5 – 145 million years
		Middle Jurassic	174.1 – 163.5 million years
		Early Jurassic	201.3 – 174.1 million years
	Triassic	Late Triassic	237 – 201.3 million years
		Middle Triassic	247.2 – 237 million years
		Early Triassic	251.9 – 247.2 million years
Paleozoic	Permian	Late Permian	298.9 – 251.9 million years
		Middle Permian	272.3 – 298.9 million years
		Early Permian	298.9 – 299 million years
	Carboniferous	Late Carboniferous	318.1 – 299 million years
		Middle Carboniferous	330.9 – 318.1 million years
		Early Carboniferous	358.9 – 330.9 million years
	Devonian	Late Devonian	383.7 – 358.9 million years
		Middle Devonian	393.3 – 383.7 million years
		Early Devonian	419.2 – 393.3 million years
	Silurian	Late Silurian	427.4 – 419.2 million years
		Middle Silurian	443.8 – 427.4 million years
		Early Silurian	443.8 – 419.2 million years
	Ordovician	Late Ordovician	458.4 – 443.8 million years
		Middle Ordovician	470 – 458.4 million years
		Early Ordovician	485.4 – 470 million years
	Cambrian	Late Cambrian	497 – 485.4 million years
		Middle Cambrian	509 – 497 million years
		Early Cambrian	541 – 509 million years
Precambrian	Proterozoic	Neoproterozoic	1,000 – 541 million years
		Mesoproterozoic	1,600 – 1,000 million years
		Paleoproterozoic	2,500 – 1,600 million years
	Archean	Neoarchean	2,800 – 2,500 million years
		Mesoarchean	3,200 – 2,800 million years
		Paleoarchean	3,600 – 3,200 million years
	Hadean		4,600 – 4,000 million years

Formation of Planets

Planets form in several stages:

1. Stars begin as concentrated clouds of gas in nebulae.
2. Gravity causes the formation of a central core.
3. A large rotating disk of gas and dust forms around this core.
4. The gas cloud begins to condense, and matter around the core turns into small, round objects.
5. These objects, called planetesimals, form as particles stick together due to cohesion.
6. Through collisions and gravitational attraction, larger bodies start to form.
7. Finally, small planetesimals come together to create larger bodies, which become planets.

Evolution of Earth

1. In the beginning, the Earth was a hot, rocky, and barren object.
2. Hydrogen and helium gases were present.
3. It formed around 4.6 billion years ago and developed a layered structure.
4. A lighter layer formed on the outer surface.
5. Density increased towards the core as you moved inward.

Evolution of Lithosphere

1. The lithosphere is the outer layer of the Earth.
2. In its early days, the Earth was very active and unpredictable. As the Earth’s density increased, so did the temperature inside its core.
3. This caused materials inside the Earth to separate based on their densities.
4. Heavier materials sank towards the center, while lighter ones rose towards the surface.
5. This process, called differentiation, led to the separation of lighter and denser materials.
6. As the lighter materials cooled, they solidified to form the Earth’s outer layer, known as the crust.
7. During the formation of the Moon, the Earth was heated up, leading to further differentiation and the formation of different layers inside the Earth.
8. These layers include the crust, mantle, outer core, and inner core.

Evolution of Atmosphere and Evolution of Hydrosphere

The evolution of the atmosphere happened in three stages. Initially, the Earth’s atmosphere consisted mainly of hydrogen and helium. Changes occurred due to solar winds. As the Earth’s core heated up and then cooled, gases and water vapor were released, leading to changes in the atmosphere, a process known as degassing. This expelled gases like hydrogen and helium from the Earth’s interior.

This started the second stage, where the atmosphere contained nitrogen, methane, water vapor, carbon dioxide, ammonia, and some oxygen. Volcanic eruptions during this stage increased gas and water vapor levels. Carbon dioxide dissolved in rainwater, leading to cooler temperatures and more rain.

The hydrosphere, or surface water, formed as rainwater collected in depressions on Earth’s surface. Finally, photosynthesis modified the atmosphere’s composition, saturating the oceans with oxygen.

Origin of Life: Short Notes

• The final phase in Earth’s evolution was the “Origin of Life”. Life began with a chemical reaction that produced complex organic molecules capable of self-replication. These molecules turned inorganic matter into living things.
• Life is believed to have started on Earth around 3.5 to 4 billion years ago. Scientists study the origin and development of life using fossils. Life evolved from single-celled organisms to more complex forms over time.
• The earliest known single-celled creatures appeared around 3.5 billion years ago, about a billion years after Earth formed. More complex life forms evolved gradually, with multicellular organisms emerging about 600 million years ago.
• The transition from simple single-celled life to multicellular organisms was a significant event in Earth’s history, dramatically changing the planet’s environment.

Conclusion

Apart from the Origin of Life, this article also covers the following topics from the chapter “The Origin and Evolution of Earth”: Formation of Planets, Evolution of Earth, Evolution of Lithosphere and Evolution of Atmosphere and Evolution of Hydrosphere. In conclusion, we’ve explored the evolution of Earth and how its layers formed. We’ve also delved into the origin of life, tracing the journey from single-celled organisms to complex life forms. It’s important to mention the Big Bang Theory when discussing life’s origin. This theory suggests that the universe, including Earth and its diverse life forms, came into being around 20 billion years ago due to a massive explosion.

Origin of Life- FAQs

What is origin of life class 11 geography?

The appearance of the simplest primordial life from non-living substances is referred to as the origin of life. The progressive creation of sophisticated species from simpler ones is referred to as evolution of life. Life evolved on Earth at least 3.5 to 4 billion years ago, and it has continued to evolve ever since.

What is the name of the chapter 2 of class 11 geography?

Chapter 2 of Class 11 Geography is called “The Origin and Evolution of Earth”.

What is the origin of the earth short notes?

The earth is thought to have formed from the accretion of small particles, or “planetesimals”, that were present in the solar nebula from which the sun and planets formed. These planetesimals were drawn together by gravity to form larger bodies, which in turn collided to form larger bodies still.

What are the 4 theories of the origin of life?

Divine creation, evolution, spontaneous generation, and cosmogenesis are the four theories of the Origin of Life.

What is the Nebular Hypothesis? 

According to this theory, the solar system arrived at its current form after collapsing from a molecular gas cloud some 4.568 billion years ago.

What is Biopoiesis?

The process of development of living organisms from non-living matter is known as biopoiesis.

What is the Theory of Biogenesis?

The theory of biogenesis states that life has evolved from pre-existing life forms.

What is the Theory of Abiogenesis?

Theory of abiogenesis states that life originated abiogenetically (suddenly and spontaneously) from any kind of non-living matter like mud, dust, etc.