Note4Students

From UPSC perspective, the following things are important :

Prelims level: Last Universal Common Ancestor (LUCA); Molecular Clock Theory; Oparin-Haldane Hypothesis; Miller-Urey Experiment.

Why in the News?

The origin of life on Earth remains one of the world’s most enduring mysteries.
- Numerous competing theories exist, but none have conclusive proof.
- A significant concept in understanding the origin of life is the Last Universal Common Ancestor (LUCA).

What is the Last Universal Common Ancestor (LUCA)?

Researchers believe that all life forms— the Bacteria, the Archaea, and the Eukarya —originated from a single cell known as the last universal common ancestor (LUCA).
It is suggested to have been a “cellular organism that had a lipid bilayer and used DNA, RNA, and protein“.
There is a lack of clarity about direct fossil evidence of LUCA.
However, the shared features of modern genomes provide significant insights into this ancient ancestor.

The molecular clock theory was proposed by molecular biologist Emile Zuckerkandl and biochemist Linus Pauling in the 1960s and later refined by biologist Motoo Kimura.
The theory allows scientists to reconstruct the evolutionary timeline.
According to the theory, the rate at which mutations are added or removed from a population’s genome is proportional to the rate of acquiring new mutations, which is constant.
By calibrating the molecular clock with known events, such as the emergence of the first mammals or the age of certain fossils, researchers can estimate the time between evolutionary events.

Researchers at the University of Bristol and Exeter estimate that LUCA originated around 4.2 billion years ago, nearly 1 billion years earlier than previously thought.
- They obtained evidence from the 3.3 km deep Candelabra’ hydrothermal vent on the Mid-Atlantic Ridge.
LUCA had a small genome of about 2.5 million bases encoding 2,600 proteins, sufficient for survival in a unique niche.
Its metabolites may have created a secondary ecosystem for other microbes.
The presence of immunity genes in LUCA suggests it had to defend against viruses.

In 1952, Stanley Miller and Harold Urey conducted an experiment at the University of Chicago, simulating lightning strikes on a mixture of methane, ammonia, and water, which resulted in the formation of amino acids.
This demonstrated that complex organic compounds could arise from inorganic compounds under the right conditions.

LUCA’s estimated origin at 4.2 billion years predates the earliest fossil records by almost 1 billion years.
Fossil records from the Pilbara Craton in Australia suggest life emerged around 3.4 billion years ago, but the study pushes this date back.

Another prominent theory suggests that meteorites from space could have brought the building blocks of life to Earth.
This theory is supported by various discoveries.
In August 2019, French and Italian scientists reported finding 3.3 billion-year-old extraterrestrial organic material.
Japan’s Hayabusa 2 mission to the asteroid Ryugu detected more than 20 amino acids, further supporting the possibility of an extraterrestrial origin for the building blocks of life.

In the 1920s, Alexander Oparin and J.B.S. Haldane independently proposed theories regarding the origin of life.
They suggested that life originated from a “primordial soup” in a prebiotic environment on the young Earth.
This concept is now known as the Oparin-Haldane hypothesis.

[2012] Which one of the following sets of elements was primarily responsible for the origin of life on the Earth?

(a) Hydrogen, Oxygen, Sodium

(b) Carbon, Hydrogen, Nitrogen

(d) Carbon, Hydrogen, Potassium