Understanding The Origin of life on earth

Date: February 17, 2017

molecules bacteria formic acid

The question of how life originated is not easy to answer because it is impossible to go back in time and observe life’s beginnings; nor are there any witnesses. There is testimony in the rocks of the earth, but it

is not easily read, and often it is silent on issues crying out for answers. There are, in principle, at least three possibilities:

  1. Special creation. Life-forms may have been put on earth by supernatural or divine forces.
  2. Extraterrestrial origin. Life may not have originated on earth at all; instead, life may have infected earth from some other planet.
  3. Spontaneous origin. Life may have evolved from inanimate matter, as associations among molecules became more and more complex.

In quest for understanding the scientific evidence for origin of life, we must look back to the early times. There are fossils of simple living things, bacteria, in rocks 3.5 billion years old. They reveal  that life originated during the first billion years of the history of our planet.


An early attempt to see what kinds of organic molecules might have been produced on the early earth was carried out in 1953 by Stanley L. Miller and Harold C. Urey. In what has become a classic experiment, they attempted to reproduce the conditions at ocean’s edge under a reducing atmosphere. Even if this assumption proves incorrect— the jury is still out on this—their experiment is critically important, as it ushered in the whole new field of prebiotic chemistry. To carry out their experiment, they (1) assembled a reducing atmosphere rich in hydrogen and excluding gaseous oxygen; (2) placed this atmosphere over liquid water, which would have been present at ocean’s edge; (3) maintained this mixture at a temperature somewhat below 100°C; and (4) simulated lightning by bombarding it with energy in the form of sparks (figure 4.6). They found that within a week, 15% of the carbon originally present as methane gas (CH4) had converted into other simple carbon compounds. Among these compounds were formaldehyde (CH2O) and hydrogen cyanide (HCN; figure 4.7). These compounds then combined to form simple molecules, such as formic acid (HCOOH) and urea (NH2CONH2), and more complex molecules containing carbon-carbon bonds, including the amino acids glycine and alanine.