B. M. Academia is for your aid let's dive deep into
Origin and evolution of Earth
Watch the video explanation here 👇
Theories About the Origin of Earth
Many scientists and philosophers have given different ideas about how Earth was formed. One of the earliest and most famous was given by Immanuel Kant, a German philosopher. Later, in 1796, Laplace, a mathematician, revised it. This idea is known as the Nebular Hypothesis.
According to this hypothesis:
- A cloud of dust and gas, called a nebula, was present around a young Sun.
- This nebula slowly started rotating.
- Due to rotation, particles in the nebula began to come together and formed planets.
In 1950, two scientists, Otto Schmidt (Russia) and Carl Weizascar (Germany), updated the Nebular Hypothesis. Their theory stated:
- The Sun was surrounded by a solar nebula made of hydrogen, helium, and dust.
- Due to friction and collision between these particles, a disk-shaped cloud was formed.
- Planets formed from this disk in a process called accretion (slow growth of particles sticking together).
Big Bang Theory: The Origin of the Universe
The most widely accepted theory about the origin of the universe is the Big Bang Theory, also called the Expanding Universe Hypothesis.
- In 1920, Edwin Hubble gave evidence that the universe is expanding.
- If you take a balloon, mark some dots on it (representing galaxies), and inflate it, the dots move apart. Similarly, galaxies in the universe are moving away from each other.
- However, galaxies themselves are not expanding, only the space between them is increasing.
The Big Bang Theory explains the universe’s formation in three major stages:
1. The Singularity (Beginning of the Universe)
- Everything in the universe was concentrated in a tiny, dense, and hot ball (singular atom).
- It had an infinite temperature and density.
2. The Big Bang Explosion (Start of Expansion)
- 13.7 billion years ago, this tiny ball exploded in a massive blast.
- This explosion caused the universe to expand rapidly.
- Some energy changed into matter, forming the first atoms within three minutes.
- The expansion slowed down later but still continues today.
3. Formation of Atoms and Transparent Universe
- In 300,000 years, the universe cooled down to 4,500K (Kelvin).
- Atoms were formed, and the universe became transparent.
Steady State Theory
Another idea was given by Hoyle, called the Steady State Theory.
- It stated that the universe always looked the same and never changed.
- However, more evidence showed that the universe is expanding, so scientists now accept the Big Bang Theory more than this theory.
Formation of Stars
- In the early universe, matter and energy were not evenly spread.
- Some areas had more gravity, pulling gas together and forming galaxies.
- A galaxy is a collection of millions of stars.
- Galaxies are huge, measuring 80,000 to 150,000 light-years across.
- A light-year is the distance light travels in a year, which is 9.461 × 10¹² km.
- The distance between the Earth and the Sun is 8.3 light-minutes.
A nebula (large cloud of hydrogen gas) collapsed due to gravity, forming stars.
- The first stars formed 5-6 billion years ago.
Formation of Planets
The process of planet formation occurred in the following steps:
1. Gas Clumps and Cores
- Inside the nebula, gas and dust came together due to gravity.
- A core formed at the center, surrounded by a rotating disk of gas and dust.
2. Creation of Planetesimals
- The gas condensed, forming small, round objects called planetesimals by process of cohesion ( Cohesion is the process by which particles of the same substance stick together due to intermolecular forces.)
- These small objects collided and stuck together, forming larger bodies.
3. Formation of Planets
- Over time, these planetesimals merged to form fewer, larger planets.
- These became the planets we see today in our solar system.
Evolution of the Earth
The Earth was not always like it is today. It was originally:
- Hot, barren, and rocky.
- Had a thin atmosphere of hydrogen and helium.
- No water or life.
Over 4.6 billion years, Earth changed into a planet with water, air, and life.
How Earth Developed Layers?
- The Earth cooled down over time.
- Heavier materials like iron sank to the center, forming the core.
- Lighter materials rose to the surface, forming the crust by process of Differentiation
The Earth’s interior separated into layers:
1. Crust (Outer layer)
2. Mantle (Middle layer)
3. Outer Core (Liquid)
4. Inner Core (Solid)
Evolution of Atmosphere and Hydrosphere
Earth’s atmosphere and water bodies developed in three stages:
1. Loss of Primordial Atmosphere
The first atmosphere of hydrogen and helium was blown away by solar winds.
2. Formation of the Second Atmosphere
- Gases like water vapor, nitrogen, carbon dioxide, methane, and ammonia came out from inside the Earth through volcanic eruptions (degassing process).
- No oxygen was present.
3. Formation of Oxygen and Oceans
- As Earth cooled, water vapor condensed into rain.
- Rain filled low areas, forming oceans (formed 4 billion years ago).
- The first life forms appeared 3.8 billion years ago.
- About 2.5 billion years ago, bacteria in oceans started photosynthesis, releasing oxygen into the air.
- 2 billion years ago, oxygen filled the atmosphere.
Origin of Life
- At first, Earth was not suitable for life.
- Scientists believe life started due to chemical reactions that formed organic molecules.
- These molecules self-replicated, creating the first living cells.
- The oldest fossils of blue-green algae are 3 billion years old.
- Life evolved from unicellular bacteria to complex plants, animals, and humans.
No comments:
Post a Comment