Life on Earth

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How Life on Earth Began

Have you ever thought about how incredible life is?

Before life could even begin on Earth some really big events needed to have happened ...


  • the Universe needed to be created from a speck of nothingness
  • the Sun had to spin into being from a cosmic cloud
  • the Earth had to make itself out of dust, & 
  • rocks from space had to fill the Earth's oceans with water 

(these events are explained in our section The Universe & Our Planet)

...and this was only the start of it

The Earth is the only planet in the solar system that has life on it, and we have not yet found another planet in the Universe that has any signs of life. This means that the earth is the only place you could ever have been you.

Why did Life Begin on Earth?

Life began on Earth because the Earth was in the right place, at the right time, with the right stuff on it. Had things been slightly different we might never have come into being.

For instance...
1.    The Earth is the right distance from the Sun 
2.    The Earth has the right mix of elements 
3.    The centre of the Earth is made of molten rock 
4.    The Earth has the right sized Moon 
5.    Life just wants to Live 

1. The Earth is the right distance from the Sun

  • If the earth had been closer to the sun it would've been far too hot for life to form.
  • If the earth had been any further away from the Sun the earth would have become a frozen ball of ice. 
  • Our closest planets are Venus and Mars, but life didn't form on either of these planets, because, unlike the Earth, the conditions weren't quite right for life to form.

2. The Earth has the right mix of elements

When you are making a cake you need to make sure you have the right mix of ingredients otherwise the cake might turn out to be something completely different, like an apple pie.

It was the same for life, the Earth was covered in the right set of ingredients, or in the Earth's case elements, for life to get started and later on become us. Had a different set of elements been on the Earth, life might have been different or it might never have occurred.

If elements are the ingredients of life, how many do you need to make life happen?

  • There are 92 naturally occurring elements on the Earth.
  • About 30 of these are found in large amounts on the Earth, the rest are fairly rare.
  • Only 6 elements are really important to life.
  • Carbon Dioxide was the most important element when it came to life beginning on Earth.

3. The centre of the Earth is made of molten rock

  • You may be wondering why a hot, liquid-rock centre would help create life?
  • Well, life would not be possible without an atmosphere. The atmosphere is, among a number of other things, the air we breath. The melted or molten rock in the centre of the Earth provided the gas that was needed to create the Earth's atmosphere. 
  • The molten rock also created a magnetic shield around the earth. This invisible barrier protects us from cosmic radiation from space. Cosmic radiation is deadly if we are exposed to it.
  • The molten rock inside the centre of the earth is always moving. This makes the surface of the Earth move. You can't see these movements as they are very gradual and happen over a long period of time. As the surface of the Earth moves it pushes some of the land up into the sky and some land down beneath the Earth's crust. This creates moutain ranges and gullies. The gullies fill with water an become seas, rivers, and lakes. This movement is called plate tectonics. If it wasn’t for plate tectonics the Earth's surface would be flat and covered in water. There would be nowhere for us to live, and all life would be sea bound.

4. The Earth has the right sized Moon

  • Although you see it every night in the sky before you go to bed, you might not realise how important the moon is to life on Earth.
  • With the help of Gravity, the moon holds the Earth steady in the sky. Without the moon our planet would wobble about in the sky. Life could not have formed on an wobbly, unstable planet. The Earth's environment would've been too changeable for life to get started.
  • The reason the Moon holds the Earth steady in the sky is because it is big compared to the Earth and therefore, with the help of gravity, has some control over the speed and angle with which the Earth spins. The Moon is about a quarter of the size of the Earth. In other words the Earth is four times bigger than the Moon. There is no other planet in the solar system with a moon as big as this. 

5. Life just wants to Live 

  • All the things listed above created the right conditions for life to get started, but on top of all of this we must remember that the amazing thing about life is that it just wants to live. This means that it made the most of everything around it just to get itself going.

What is Life?

What is the difference between being alive and not being alive?

Living things...

  1. Move
  2. Grow
  3. Reproduce
  4. Die
  5. Respond to changes in their surroundings
  6. Have many Chemical Reactions taking place inside the
  7. Are made of cells

1. Most Living Things Move 

  • Animals move because they need to find food, shelter, and avoid danger.
  • Plants also move, but in a different way to animals. Pants need energy from the Sun to live so turn themselves to face it.

2. Living Things Grow 

  • Rocks don't get bigger as they get older, but you do and so do all the animals and plants you can think of. Your body uses the energy it gets from food to help it grow stronger. All living things start life small and then get bigger as they get older.

3. Living Things Reproduce 

  • This is where living things create other living things. When a living thing reproduces it passes some of its characteristics onto the next generation. For instance, you may be a fast runner like your Mum. 

4. Living Things Die

  • All living things will eventually die. Living things want to be alive, so spend most of their day doing the things that will keep them alive for as long as possible, like looking for food, water and shelter and protecting themselves from danger.

5. Living things can respond to changes in their surroundings 

  • This is a very important part of staying alive. Living things respond to the environment around them. For example, if it starts snowing, you will look for somewhere warm to shelter; whereas a rock will just sit in the garden and get covered in snow. If you are too hot your body will start to sweat to cool you down. You sneeze, to stop dust and germs from entering your body through your nose. If there is no food where you are living you will move to somewhere where there is food.

6. Chemical reactions take place inside living things

  • Many chemical reactions are happening inside your body just now. These chemical reactions are what make life possible; they change the food you eat into energy, which your body uses to make it work, which is why you must chose what food you eat wisely. Chemical reactions tell your body how to respond to the things happening around it. For example, to get out of the way if a big rock is rolling down a hill towards you; to shiver if you are cold to help your body keep warm; to clot your blood if you cut yourself with a sharp knife. 
  • Chemical reactions also happen in things that are not alive, but at no where near the same levels. 

7. Living things are made of cells

  • All living things are made of cells. Your skin, hair, fingernails, blood, bones, and every other part of your body are made up of millions of cells. These cells work together to keep you alive.

How did life start itself on the Earth?

  • Would you believe me if I told you that life on Earth began as a sea of soup. This soup was made up of a mixture of chemical elements.
  • It was called Primordial Soup and, although it wasn't alive, it had all the elements needed to create life.
  • In order for the soup to come alive the chemicals had to first make some cells.
  • Cells are like little protective bags. Once safely inside a cell, the chemicals could start working together to make life happen.
  • How and why the first cell formed in the Primordial Soup is still a mystery. It's believed that a spark of energy in the soup set off a chemcal reaction that made the cells and something called amino acids, which were, and still are, the "building block of life".
  • The source of the spark of energy could have been either lightening, the sun, a meteorite or something completely different, we're not sure, we just know that somehow life began.

What are cells?

  • Cells are the smallest living thing you can get, but it is not the smallest thing that exists. 
  • A cell is made of atoms, but an atom is still not the smallest thing that exists.
  • An atom is made up of subatomic particles, which are made of elementary paticles. Nothing in the Universe is smaller than an elementary particle.
  • Our bodies are made up of billions of cells.
  • Each cell has a little job to do to help to keep you alive.

The first form of life on earth was very simple compared to life as we know it today. It was made of only one cell and it just hung around in the sea doing not much at all apart from living. It didn't go to school, watch TV, ride its bike or eat sweets.

In fact the first type of life on earth probably just ate Primordial Soup, moved around a bit and made lots more of itself. They were bacteria and algae.

After several million years, the first living cells had eaten so much Primordial Soup that they were going to run out. This meant that soon there would be nothing left for all the new cells they were busy creating to eat. If they wanted to survive they would need to change the way they lived. This is the first example of living things adapting themselves to live in their changing surroundings. What happened was, over time, these cells stopped eating Primordial Soup and started to create their own food. They made food from the chemicals around them and from the heat from the Sun and the Earth. This stopped them from dying out. 

The first living cells had changed the way they did things in order to survive in their new surroundings. This is called Evolution.

After many more Evolutionary changes, over many millions of years these simple cells would eventually become life as we know it today - in other words these cells would become US. 

Move onto next section about What People are made of ....

         What are we made of? Cells

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