1. THE EARTH: PLANET OF LIFE

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The Earth is the only planet in the Solar System on which life has been found. The Earth provides perfect conditions for hosting life:

Video 1: How life on Earth began

1.1. The origin of life

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The oldest remains of life ever found date back 3600 million years. The origin of life on Earth is one of the most important scientific issues. There are several theories regarding the origins of life:

Chemical evolution theory. This theory claims that life on Earth started from certain chemical elements found in the atmosphere. The Sun's radiation and electrical charges allowed these elements to organise themselves into more complex molecules.

Molecules accumulated in primitive seas and evolved until they formed simple unicellular organisms. These organisms continued to evolve and diversify until they became the living things we find on Earth today.

During this process, living things changed the characteristics and composition of the atmosphere.

Exogenesis theory: This theory suggests that life on Earth came about because of a comet or a meteorite that crashed into our planet. This theory is starting to be more widely accepted as a result of scientific evidence found on Mars.

1.2. Common characteristics in living things

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Although there is a great diversity of living things on our planet, they all share certain characteristics:

Chemical elements found in living things are different from those found in non-living things.
Living things have exclusive molecules which are not found in non-living things.
Living things are made of cells and perform various vital functions: nutrition, interaction and reproduction.

1.3. Levels of organisation found in matter

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The matter which all living things consist of is organised into a structure. This structure has various organisational levels of increasing complexity.

Key concepts

The Earth has certain characteristics that make life possible.
Matter organises itself into many levels. The cell and the structural levels above it are unique to living beings.

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Look at these levels of organisation. Which ones are common to both living things and non-living things?

Look up information about the Solar System, then mark whether the following sentences explaining why there can be life on Venus are true or false:

1. The absence of liquid water helps living beings complete their cellular processes.

True

False
Correct answer

Wrong answer
2. Because of its short distance from the sun, Venus's surface temperature is very high. This is why it is difficult to find liquid water.

True

False
Correct answer

Wrong answer
3. Venus's atmosphere is very thick. This provokes a strong greenhouse effect that makes Venus's average temperature 480°C.

True

False
Correct answer

Wrong answer

3. Listen and say whether these sentences are true or false. Correct the false sentences.

a)

True

False
Correct answer

Wrong answer
b)

True

False
Correct answer

Wrong answer
c)

True

False
Correct answer

Wrong answer

Correct the false senctences in the box below:

Write three characteristics that differentiate a rock from a living thing.

Match the follwong words to their definitions:

atom
molecule
organism

a group of atoms
the smallest unit of matter
a multicellular, individual living thing

Are all the levels of organisation exclusive to living things?

Give reasons for your answer.

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