Chapter 13: Our Home: Earth, a Unique Life Sustaining Planet (Earth Science)

Mars has only a very thin atmosphere and no liquid water on its surface. (It is farther from the Sun than the Earth, and it has almost no magnetic field.)

(iii)

Geodiversity is the variety of non-living features: rocks, minerals, soils and landforms. Options (i) and (iv) are about biodiversity, and (iii) is about weather.

(ii)

A smaller Earth would have less mass and weaker gravity. Gas particles could then escape more easily, so over time much of the air would be lost, as happened on Mars.

(ii)

Each parent passes on half of its genes, and these combine in a new way in each offspring. This creates variation.

(iv)

Where the seeds came from: tiny, light seeds and spores are carried by the wind. Others are dropped by birds (in their droppings) or carried by ants, or washed in by rainwater. Some (mosses and ferns) grow from spores.

What helped them grow:

• moisture from the monsoon rains;
• a little soil and dust collected in the cracks;
• sunlight;
• warm temperatures.

The cracks also protect the young roots.

Seeds and spores are carried by wind, birds, ants and rain; the monsoon moisture, dust and soil in the cracks, sunlight and warmth let them sprout.

Climate:

• The area becomes hotter: trees no longer shade the ground or cool the air, and concrete and tar absorb heat (an urban heat island).
• The air becomes drier, possibly with less local rainfall.
• More dust and pollution, and less carbon dioxide is absorbed.

Biodiversity:

• Birds, insects, small mammals and plants lose their homes and food.
• Many species die out locally, while others, such as monkeys and snakes, may enter homes.
• Pollinators decline, which affects nearby crops and gardens.

Water:

• Rain falls on hard surfaces and runs off instead of soaking in, so less groundwater is recharged and wells and borewells may dry up.
• Sudden run-off can cause flooding.
• Without roots to hold it, soil erodes and muddies lakes and streams, and run-off carries pollutants into them. Water quality falls.

The area becomes hotter and drier with more pollution; plants and animals lose their habitat; less rainwater soaks into the ground, causing falling groundwater, flooding and muddier, more polluted water.

It is true that the climate has changed before, for example during the ice ages and the warm periods between them. But today's warming is different:

• Cause: past changes came from natural causes, such as small changes in the Earth's orbit, volcanoes and changes in the Sun. Today's warming is mainly caused by human activities: burning coal, oil and gas, and cutting forests. These add carbon dioxide and other greenhouse gases that trap heat.
• Speed: natural changes took thousands of years. The Earth has warmed by about 1.1 °C in only about 150 years, which is far faster than plants, animals and people can easily adjust to.
• Effects: melting glaciers, rising seas, stronger heatwaves, floods, droughts and cyclones are already affecting crops, water supplies and health around the world.

Because we are causing it, we can also reduce it: by using clean energy, saving electricity and fuel, and protecting and planting forests.

Past climate changes were natural and slow; today's warming is fast and caused mainly by humans adding greenhouse gases, so it is new, and we can act to reduce it.

• Harmful particles from the Sun (the solar wind and solar storms) would no longer be deflected. Over a long time, they could strip away parts of the atmosphere, as on Mars. More harmful radiation would reach high altitudes and space.
• Animals that navigate using the magnetic field, such as migratory birds, sea turtles and some fish, would lose their way.
• Compasses would not work.
• Satellites, power grids and communication systems could be damaged by solar storms more easily.

Without it, charged particles from the Sun could erode the atmosphere and damage satellites and power grids, migrating animals would lose their way, and compasses would stop working.

1. Breathable air at the right pressure: oxygen to breathe and a sealed, pressurised dome, because Mars's air is very thin and mostly carbon dioxide.
2. Liquid water: melted from underground ice, cleaned and recycled.
3. A safe temperature and protection from radiation: heating against the cold of about −60 °C on average, and thick walls, or shelters underground, against radiation.

(Also needed: a way to grow food in soil or water.)

Hardest: a thick atmosphere together with radiation shielding. Mars has weak gravity and no global magnetic field, so it cannot hold on to a thick atmosphere or keep out harmful radiation. Everyone would have to live inside protected buildings.

Air (oxygen at the right pressure), water, and warmth with radiation protection (plus food). The hardest is a protective atmosphere and radiation shield, because Mars's weak gravity and lack of a magnetic field cannot keep one.

Possible causes:

• Climate change from global warming, due to greenhouse gases from burning fuels;
• local causes such as cutting trees and forests nearby, and the drying of ponds and wetlands.

Ways to adapt:

1. Save water: rainwater harvesting, check dams, reviving ponds, and drip or sprinkler irrigation.
2. Change farming: grow drought-tolerant crops (such as millets), change sowing dates, and mix crops so that one failure doesn't ruin everything.

Planting trees around fields and homes also gives shade and cools the area.

Probably climate change (and local tree cutting). Adapt by harvesting and saving water, and by growing drought-tolerant crops with changed sowing times (plus planting trees).

• Life: there would be no oxygen to breathe and no carbon dioxide for plants, so no life as we know it. There would also be no protection from the Sun's harmful ultraviolet rays, or from meteoroids, which now burn up in the air.
• Temperature: without the air acting as a blanket, days would be extremely hot and nights extremely cold, as on the Moon.
• Water: with no air pressure, liquid water would boil away and escape into space. There would be no clouds, rain or water cycle, and no rivers or oceans.

(Sound also needs air to travel, so the Earth would be silent.)

There would be no air to breathe, no protection from UV rays and meteors, extreme temperatures between day and night, and no liquid water or rain, so life could not exist.

In vegetative propagation, new plants grow from a root, stem or leaf, not from seeds:

1. Potato: the "eyes" (buds) on a stem tuber sprout into new plants.
2. Sugarcane: pieces of stem with nodes are planted, and shoots and roots grow from the nodes.
3. Rose or money plant: a stem cutting planted in moist soil grows roots.
4. Bryophyllum: small plantlets grow from buds on the edges of its leaves.
5. Ginger or turmeric: an underground stem (rhizome) produces new shoots.

Other examples: onion (bulb), strawberry and grass (runners), banana (suckers), sweet potato (roots). The new plants are exact copies of the parent and grow faster than plants from seed.

Potato (tuber eyes), sugarcane (stem nodes), rose or money plant (stem cuttings), Bryophyllum (leaf buds), ginger (rhizome), and also onion, strawberry and banana.