Introduction

▓ A common question that still bothers many scientists in the past and present is “HOW DID THE EARTH BEGIN?”

▓ Various theories have been put in place to determine the origin of Earth and the events that occurred since.

▓ By combining various knowledge, evidence and theories contributed by global scientists; we now have a satisfactory understanding on how the earth originated [with the help of various methods such as carbon or uranium dating].

▓ We also have the ability to produce a timeline of how life began…

Formation of the Solar System (4.57 billion years ago)

According to scientists, our Solar System was formed from a giant rotating

cloud of gas and dust (protoplanetary disc).

The sun was formed at the centre of the disc and the planets gradually

formed around the sun due to the process of accretion.

Formation of the Moon (4.53 billion years ago)

• The “Giant Impact” hypothesis states that the moon formed as a result of a

collision between the Earth and a Mars-sized body called Theia.

• The impact caused a portion of the combined mantle of the Earth and Theia

to be expelled into space, eventually forming the Moon.

Late Heavy Bombardment(4.1 – 3.8 billion years ago)

• Based on observations of impact craters on the moon, many astronomers

believe that the Earth endured a violent period of near constant collisions with

large asteroids and comets.

Formation of the Earth’s Crust & Oceans(4 Billion Years Ago)

• The cooling of the Earth allowed for crust formation and the condensation of

water present in the atmosphere, forming the Earth’s oceans.

Oldest Geographical Evidence of Life (3.5 Billion Years Ago)

• Stromatolites (rock formations) were formed as a by-product of microbial life.

• During the formation, sheets of microbes such as cyanobacteria capture

sedimentary particles.

Proliferation of Cyanobacteria (3.0 – 2.5 billion years ago)

• Ancestors of modern cyanobacteria may have thrived on

the earth as early as 3 billion years ago.

• The evolution of photosynthesis allowed cyanobacteria to

convert light energy to chemical energy.

• The formation of oxygen molecules as a by-product of

photosynthesis eventually transformed the Earth’s

atmosphere and paved the way for the growth in

biodiversity on the planet.

Evolution of Cells with Nuclei – Eukaryotes(2.0 billion years ago)

• Geographical evidence suggests that life on Earth

was limited to prokaryotic, bacteria-like life until

around 2 billion years ago.

• Modern eukaryotes are characterised as having

membrane-bound organelles, such as

mitochondria, chloroplasts and membrane-bound

nucleus.

• The bacteria that went on to become organelles

transferred the bulk of their genetic information to

the host cell genome and lost their ability to survive

independently.

Evolution of Multi-cellular Organisms (1.2 billion years ago)

• According to some hypotheses, multicellularity evolved as a result of

symbiotic relationship between cells of the same or different species,

eventually leading to independency.

Cambrian Explosion(600-500 million years ago)

• The fossil record shows a sharp increase in the diversity and number of

complex animals during a relatively short time span in Earth’s history.

• The cause of the Cambrian Explosion is unknown, although many scientists

suspect that the rise in atmospheric oxygen or other environmental changes

may have played a significant role.

Reign of the Dinosaurs(230-65 million years ago)

• For over 150 million years, dinosaurs have populated the Earth.

• Their extinction (also known as the Cretaceous-Tertiary extinction Event) is

thought to have been caused by a large asteroid impact or an increase in

volcanic activity.

Appearance of Modern Humans(200 thousand years ago)

• Appearance of modern humans (200 thousand years ago)

• Paleontological evidence suggests that modern humans evolved from Homo

erectus (a species of extinct humans) approximately 200 thousand years ago.

• The current human population is estimated to be over 6.5 billion, with humans

inhabiting every continent on the Earth.

MY BIBLIO www.bbc.co.uk/science/earth/earth_timeline

www.livescience.com/13363-7-theories-origin-life.html

www.shmoop.com/special-topics-evolution/life-origin.html

www.globalcommunity.org/wtt/walk_photos/print_pages/4600.htm

www.science.nationalgeographic.com.au/science/prehistoric-

world/prehistoric-time-line/

http://exploringorigins.org/timeline.html