Natural sciences Year 5: Earth, life and its environments
Natural sciences, Year 5 (Portugal): Why there is life on Earth, the four Earth subsystems, and how to tell land environments from water environments using field data.
A planet with the conditions for life
Earth is the only planet where we know there is life. It has liquid water, because the temperature at the surface is mild, and an atmosphere with the gases living things need, such as oxygen and carbon dioxide. The atmosphere also filters part of the Sun's radiation and stops the temperature from swinging to extremes. It is the three conditions together that make life possible, not any one of them alone.
Four subsystems that interact
We study the planet as four subsystems: the geosphere (rocks, soil and the Earth's interior), the hydrosphere (all the water), the atmosphere (the air around the Earth) and the biosphere (all living things). They are not separate boxes: rain from the atmosphere fills a river (hydrosphere), wears down rocks (geosphere) and keeps plants alive (biosphere). A change in one ends up affecting the others.
Land or water: reading field data
Example data (made up for the exercise). Cork-oak pasture: air between 12 °C and 32 °C in one day, sunlight reaching the ground. Pond: water between 17 °C and 21 °C, light fading with depth. Step 1: compare the swings: 32 − 12 = 20 °C against 21 − 17 = 4 °C. Step 2: compare light and water. Step 3: conclude: on land the air changes a lot and water can be scarce; in water it never runs out and the temperature is steadier.
One condition is not enough
A common idea is «there is life on Earth because it has oxygen» (or because it has water). Each one alone is not enough. The Moon has almost no atmosphere: without one, its temperature goes from over 100 °C by day to about −170 °C at night, and liquid water cannot stay on the surface. On Earth, liquid water, a suitable atmosphere and a mild temperature work together.
A document with all four subsystems
On 1 November 1755 an earthquake struck Lisbon, followed by a tsunami and fires. In a text about that day you can find the geosphere (the shaking ground), the hydrosphere (the sea waves and the Tagus), the atmosphere (the air full of smoke from the fires) and the biosphere (the people and animals affected). History and Geography of Portugal help you place these subsystems in a real event.
Test what you learned
Which conditions together make life possible on Earth?
- a) Oxygen in the air, and nothing else
- b) Liquid water, a suitable atmosphere and a mild temperature
- c) Plenty of sunlight, and nothing else
Correct answer: b) Liquid water, a suitable atmosphere and a mild temperature — Right: it is the three conditions working together that make life possible on Earth.
Example data: air in a pasture varied from 12 °C to 32 °C in one day; pond water from 17 °C to 21 °C. Which conclusion fits?
- a) The temperature changes more in the pond
- b) The temperature changes the same amount in both
- c) It changes more on land (20 °C) than in the pond (4 °C)
Correct answer: c) It changes more on land (20 °C) than in the pond (4 °C) — Right: 32 − 12 = 20 °C on land against 21 − 17 = 4 °C in water.
A classmate says: «there is life on Earth only because there is oxygen». What is the best reply?
- a) Oxygen is not enough: liquid water and a mild temperature are needed too
- b) Yes, oxygen is the only condition life needs
- c) No, oxygen plays no part in life on Earth
Correct answer: a) Oxygen is not enough: liquid water and a mild temperature are needed too — Right: the Moon shows that one condition alone is not enough for life.
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