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Conditions for Life
Conditions for Life
From the BGE Science course, it has been shown that in order for life (as we know it) to exist, four fundamental needs must be addressed:-
From the BGE Science course, it has been shown that in order for life (as we know it) to exist, four fundamental needs must be addressed:-
1. Water (in liquid form).
1. Water (in liquid form).
2. Essential chemicals for living processes.
2. Essential chemicals for living processes.
3. A surface for processes to occur on/in.
3. A surface for processes to occur on/in.
4. Energy to fuel these processes.
4. Energy to fuel these processes.
What is Life ?
What is Life ?
One a the big issues with the search for life is deciding on what life is. In film and literature, Aliens always look vaguely human-like, but there is no reason at all that alien life should!
One a the big issues with the search for life is deciding on what life is. In film and literature, Aliens always look vaguely human-like, but there is no reason at all that alien life should!
So how do we decide what is alive and what isn't ?
So how do we decide what is alive and what isn't ?
One way scientists decide if something is living is to see if it performs the seven fundamental Life Processes:-
One way scientists decide if something is living is to see if it performs the seven fundamental Life Processes:-
M - Movement - All living things move e.g. animals move to hunt or a plant moves towards the sunlight.
M - Movement - All living things move e.g. animals move to hunt or a plant moves towards the sunlight.
R - Respiration - All living things use an energy source to create usable Energy e.g. animals use the energy from food
R - Respiration - All living things use an energy source to create usable Energy e.g. animals use the energy from food
S - Sensitivity - All living things react to their environment e.g. animals move away from hot objects or a flower opens in sunlight.
S - Sensitivity - All living things react to their environment e.g. animals move away from hot objects or a flower opens in sunlight.
G - Growth - All living things grow e.g. babies become adults or seeds become plants.
G - Growth - All living things grow e.g. babies become adults or seeds become plants.
R - Reproduction - All living things reproduce e.g. animals have babies or plant make seeds.
R - Reproduction - All living things reproduce e.g. animals have babies or plant make seeds.
E - Excretion - All living things give out waste products e.g. animals breathe out Carbon Dioxide or plants release Oxygen.
E - Excretion - All living things give out waste products e.g. animals breathe out Carbon Dioxide or plants release Oxygen.
N - Nutrition - All living things take in chemicals from their environment e.g. animals eat food or plant absorb nutrients from the soil.
N - Nutrition - All living things take in chemicals from their environment e.g. animals eat food or plant absorb nutrients from the soil.
Is it Alive ?
Is it Alive ?
Whether something is alive seems like an easy decision using the above processes, but it is not always the case. The image below shows some examples of this:-
Whether something is alive seems like an easy decision using the above processes, but it is not always the case. The image below shows some examples of this:-
Where can Life Exist ?
Where can Life Exist ?
As stated above, one of the main requirements for life is liquid water, which means that there are only certain places in the Universe that life could exist.
As stated above, one of the main requirements for life is liquid water, which means that there are only certain places in the Universe that life could exist.
Liquid water can only exist in locations where the temperature is between the freezing and boiling points of water.
Liquid water can only exist in locations where the temperature is between the freezing and boiling points of water.
1. Too close to parent star - Surface Temperature too high, water in vapour form only or has been lost to space.
1. Too close to parent star - Surface Temperature too high, water in vapour form only or has been lost to space.
2. Too far from parent star - Surface Temperature too low, water locked in solid form (ice).
2. Too far from parent star - Surface Temperature too low, water locked in solid form (ice).
3. Band 'in between' - Habitable Zone, Surface Temperature 'just right', water in liquid form.
3. Band 'in between' - Habitable Zone, Surface Temperature 'just right', water in liquid form.
The image above shows a visual representation of our Solar System's Habitable Zone. As can be seen, based upon distance from the Sun, three planets lie within this zone, Venus, Earth and Mars.
The image above shows a visual representation of our Solar System's Habitable Zone. As can be seen, based upon distance from the Sun, three planets lie within this zone, Venus, Earth and Mars.
Habitable Zone Size
Habitable Zone Size
The Size of the Habitable Zone varies from star to star. The larger and hotter a star, the further from the star the Habitable Zone is. The below image shows the size of the Habitable Zone around the white-dwarf star Kepler-186 as compared to our Solar System. The planet Kepler-186f is the first Earth-sized planet to be discovered orbiting within its parent star's Habitable Zone:-
The Size of the Habitable Zone varies from star to star. The larger and hotter a star, the further from the star the Habitable Zone is. The below image shows the size of the Habitable Zone around the white-dwarf star Kepler-186 as compared to our Solar System. The planet Kepler-186f is the first Earth-sized planet to be discovered orbiting within its parent star's Habitable Zone:-
Life outside the Habitable Zone
Life outside the Habitable Zone
The Habitable Zone is a good place to look for life, but is not the only location life could occur. Even within our own Solar System, there are locations beyond the Habitable Zone which could support life.
The Habitable Zone is a good place to look for life, but is not the only location life could occur. Even within our own Solar System, there are locations beyond the Habitable Zone which could support life.
1. Europa - One of Jupiter's moons, possible liquid ocean under a surface layer of ice, kept liquid by Tidal Heating due to Jupiter's immense Gravity.
1. Europa - One of Jupiter's moons, possible liquid ocean under a surface layer of ice, kept liquid by Tidal Heating due to Jupiter's immense Gravity.
2. Titan - One of Saturn's moons, only moon in our Solar System to have a significant atmosphere. Liquid Hydrocarbon lakes could possibly sustain life in a similar way to the water cycle on Earth.
2. Titan - One of Saturn's moons, only moon in our Solar System to have a significant atmosphere. Liquid Hydrocarbon lakes could possibly sustain life in a similar way to the water cycle on Earth.
We have Liquid Water, now what ?
We have Liquid Water, now what ?
Once a planet is found in the Habitable Zone and could have liquid water, the next important factor is whether the planet has an atmosphere.
Once a planet is found in the Habitable Zone and could have liquid water, the next important factor is whether the planet has an atmosphere.
All living things need to take in chemicals from the environment and an atmosphere is a vital part of that.
All living things need to take in chemicals from the environment and an atmosphere is a vital part of that.
For example:-
For example:-
This means, in order for living things to survive, the atmosphere must contain specific useful gases.
This means, in order for living things to survive, the atmosphere must contain specific useful gases.
The gases that make up the Earth's atmosphere have changed a lot since the Earth was formed. The video below shows a detailed view of the formation of the Earth and its atmosphere:-
The gases that make up the Earth's atmosphere have changed a lot since the Earth was formed. The video below shows a detailed view of the formation of the Earth and its atmosphere:-
The present day atmosphere of the Earth contains mostly Nitrogen and Oxygen, as well as trace amounts of lots more:-
The present day atmosphere of the Earth contains mostly Nitrogen and Oxygen, as well as trace amounts of lots more:-
The Life of Plants
The Life of Plants
Without plants, the composition the Earth's atmosphere would be very different. All of the Oxygen in the atmosphere was released by plants or algae as a waste product.
Without plants, the composition the Earth's atmosphere would be very different. All of the Oxygen in the atmosphere was released by plants or algae as a waste product.
It was only after there was a large amount of Oxygen in the atmosphere that Oxygen breathing life could evolve, using the plant's waste product for Respiration. The Process which causes the Plant to release Oxygen is known as Photosynthesis.
It was only after there was a large amount of Oxygen in the atmosphere that Oxygen breathing life could evolve, using the plant's waste product for Respiration. The Process which causes the Plant to release Oxygen is known as Photosynthesis.
The process of Photosynthesis allows the plant to use the Sun's energy to create simple sugars, a food source for the plant.
The process of Photosynthesis allows the plant to use the Sun's energy to create simple sugars, a food source for the plant.
The diagram below shows the word equation for Photosynthesis:-
The diagram below shows the word equation for Photosynthesis:-
The process of Photosynthesis occurs inside the plant within a structure of the cell called the Chloroplasts.
The process of Photosynthesis occurs inside the plant within a structure of the cell called the Chloroplasts.
The Chloroplasts contain a chemical called Chlorophyll which absorbs the sunlight that falls on the plant. It is the bright green Chlorophyll that gives green plants their colour.
The Chloroplasts contain a chemical called Chlorophyll which absorbs the sunlight that falls on the plant. It is the bright green Chlorophyll that gives green plants their colour.
The image below shows Chloroplasts within a Leaf:-
The image below shows Chloroplasts within a Leaf:-
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