Life on Earth-Outcome 1.1-1.4
Most cultures have developed an explanation for the beginning of Life on Earth. This
usually includes creation by a mighty being controlling the destiny of Earth. However,
scientists have the task of seeking an explanation based on scientific evidence.
As new technologies are developed, new ideas arise and scientific ideas and
explanations are modified.
Evidence about cells show that they are the basic unit of life on Earth.
We are going to look at the current scientific explanation for the origin of simple
cells.
Outcome 1
Analysis of the oldest sedimentary rocks provides evidence for the origin of life
1.1 Identify the relationship between the conditions on early Earth and the origin of
organic molecules
 Scientists estimate that the universe is 10-20 billion years old and arose as a “big
bang”, which is still expanding the universe.
 Some matter in the universe came together or condensed to form solar systems
and galaxies.
 Our Earth is thought to have begun about 4.5 billion years ago.
 The early Earth was very different from the Earth today. As the earth cooled
from about 1000oC to below 100oC, clouds of water vapour condensed to form
oceans and the atmosphere consisted of the gases, hydrogen, carbon monoxide,
methane and ammonia. No oxygen was present.
 As rain began to fall, erosion produced sediments that gradually formed into
sedimentary rocks. The oldest sedimentary rocks that still exist on Earth
 On our Earth, organic chemicals appear to have originated about 4 billion years
ago.
 Scientists have hypothesized about how this happened and tested their
hypotheses.
1.2 Discuss the implications of the existence of organic molecules in the cosmos for
the origin of life on Earth
 For many centuries, humans believed that life spontaneously arises from nonliving matter. This is called spontaneous generation.
 The experiments of Redi, Spallanzani and Pasteur, carried out over a period of
200 years disproved this theory.
1.3 Describe two scientific theories relating to the evolution of the chemicals of life
and ……
 Oparin and Haldane believed that organic chemicals were produced from nonliving matter on the early Earth. Their hypothesis was tested by Urey and
Miller in the 1950’s.
 Urey and Miller found living matter when they simulated conditions on early
Earth. Organic molecules are complex carbon-based molecules, including
amino acids, that are the building blocks of protein. This supported Oparin and
Haldane’s hypothesis and was called the chemosynthetic origin of life.
 The chemicals from outer space (Panspermia) are another hypothesis.
 Scientists agree that the evolution of living chemicals was a significant first
step in the evolution of life. The evolution of cells and more complex life
forms depended on it because cells are highly organised arrangements of
biological chemicals.
 Evidence exists that the first living organisms may have had RNA as their
genetic material.
#evolution: the gradual changes that have transformed the earliest life forms to the
diversity of life found today.
1.3 cont….. discuss their significance in understanding the origin of life
 Chemical evidence of life exists from 3850 mya.
 The first living organisms probably used organic molecules from their
environment as their energy source.
 Later, new forms of life evolved that used sunlight as their energy source and
made their own organic molecules via photosynthesis.
 Oxygen released by the earliest photosynthetic microbes was at first mopped
up by dissolved ferrous iron to form insoluble ferric oxide. The rocks , known
as banded iron formations, provide evidence when the first free oxygen was
released into the atmosphere.
 By about 2000mya, free oxygen began to accumulate in the atmosphere,
converting the anoxic state to an oxic state.
1.4 Discuss the significance of the Urey and Miller experiments in the debate on the
composition of the primitive atmosphere
 The research of Urey and Miller led other scientists to investigations in this
area, pushing forward knowledge about the beginning of life.
1.6 Gather information from secondary sources to describe the experiments of Urey
and
Miller and use the available evidence to analyse the:
–
reason for their experiments
–
result of their experiments
–
importance of their experiments in illustrating the nature and practice
of science
contribution to hypotheses about the origin of life
1. Why did Urey and Miller carry out their experiments?
To test the theories of Oparin and Haldane, that the early components of earth
could be used to make organic molecules.
2. In the apparatus used by Urey and Miller, what did the following represent?
a. the electrical discharges lightning
b. the gases used atmosphere on early Earth
c. the water in the flask oceans
3. Why was the water heated and then cooled? Simulate conditions on early earth
which did not have ozone layer and so had extreme conditions.
4. What was the result of their experiments? They showed that organic molecules
such as amino acids could be formed under these conditions.
5. What do their experiments demonstrate about the nature and practice of
Science?
That a theory can be developed, and then other scientists can work on that
theory and contribute to the general understanding. Other examples include
the discovery of the structure of DNA. The work done by Urey and Miller was
just the beginning of scientific studies to determine how life began on Earth.
6. What contributions did Urey and Miller make to hypotheses about the origin
of life?
By proving that organic molecules could be formed from inorganic molecules,
they showed the possibility of how life on Earth could begin.