“So where did all this life come from?”
Excellent question and like all the best questions is very hard to answer. We do know that there has been life on earth for a very long time. The earth is around 4,500 million years old and the first forms of life are thought to have been primitive bacteria that appeared around 3,500 million years ago.
“How can anyone know that?”
These bacteria left fossilized rocks called stromatolites, scientists know these rocks were made by simple bacteria because they are still alive today in parts of Australia. Here's a picture of them.
“They look like rocks.”
Well spotted, but they are rocks made by the bacteria as they grow.
“So everything came from these rock-making bugs?”
Well not necessarily those exact bacteria but something very similar. The fact that all living things use DNA, the stuff we talked about last time, suggests all life on Earth came from a some simple original life form. That life-form changed and more complicated versions appeared. Over millions of years new life-forms and creatures developed from this very simple start. That’s what evolution is all about.
“The thing that Charles Darwin discovered?”
That’s the one. One of the strongest pieces of evidence for evolution is that DNA alphabet I told you about is shared by every living creature. But Charles Darwin didn’t know about DNA, he developed his theory of evolution by examining the different types of animals on a tiny set of islands in the Pacific Ocean, the Galapagos Islands. He found that birds on different islands had changed so they were best suited to eating particular types of food. From these little changes he suggested that if you string together lots of little changes over millions of years you can explain how any living creature could evolve from a simple common ancestor.
“I can just about believe that all the different forms of life evolved from one very simple creature, with a lot of imagination. But where did that first creature come from?”
Hmm, I thought I might have got away with not answering that question. Where life first came from must rate as one of the universe's really big questions. It’s one of the universe’s big questions exactly because no-one has answered it yet. For most scientists, life came by random chemical reactions over millions of years suddenly kick-starting life.
“Life just started out of the blue by chance? That seems a little unlikely.”
There are plenty of scientists who’d agree and suggest life just happening would be like a hurricane passing through a junk yard and creating a pristine Boeing 747. Or a million chimpanzees randomly hitting keys on a million keyboards and suddenly one of them writes one of Shakespeare’s plays. So some people have suggested that life came from space and landed on Earth from a comet or asteroid. There is another idea that was put put forward by Francis Crick, one of the scientists who discovered the shape of DNA. He suggested that life was deliberately put here on Earth by intelligent space travelling aliens.
“What? Was he mad?”
No, I think it was a well thought out idea if a little unusual. After all our galaxy has been around for billions of years before the Earth even formed, so if life could start once it could start many times.
So if it possible for life to start by chance, then it is likely to have happened more than once. As the universe has been in existence about 9 billion years longer than the Earth, it is likely that life started somewhere else first. Crick and his colleague Leslie Orgel pointed out that living things need a very rare element called Molybdenum to stay healthy. This is very rare on Earth but seems much more common in other star systems. So they argued that it was more likely that life started on a planet with lots of molybdenum. This theory has wonderful name of 'Directed Panspermia'.
“Life reaching earth from outer space sounds a bit weird but it doesn’t really answer the question. Even if I believe that, how did life start in outer space?”
You’re absolutely right, life has to come from somewhere and saying life on earth came from another planet doesn’t answer the real question. The real answer is that no-one really knows where life came from. What makes it a bit more believable that life could have developed out of the blue is that some of the molecules that really important for living creatures, like amino acids, have been detected in space dust. There is even alcohol floating around between clouds.
“Couldn’t that just be bits left over from a pub on some planet that blew itself up or got blown up?”
It could be, but these amino acid molecules can be created out of the simple gases found in space. There are 20 different type of amino acid in living things on earth and they are the building blocks of proteins. All those words in the DNA alphabet are instructions to make proteins. Proteins are strings of amino acids and each three letter word in the DNA alphabet tell which amino acid goes where. Proteins are the second most important molecule in living things after DNA. DNA has the instructions, but proteins are the molecules that do all the important jobs in living things.
“Like the musicians in your ‘life as an orchestra idea’.”
Just so. With radio-telescopes, astronomers have found these amino acids in space. The right combination of gases and light can just make atoms combine into these building blocks of life. So at least some of the raw materials are out there in space. Even more interesting was a shower of meteorites that landed in Australia on September 28, 1969. These were collected and investigated by NASA. Remarkably these meteorites contained 90 different types of amino acid including 19 of the amino acid found in living things on earth. So the other 71 types of amino acids that don’t exist naturally on earth can only have come from outer space.
“Alien amino acids?”
Possibly. Another meteorite ALH84001 was found hidden in snow in Antarctica in December 1984. Scientists believe this meteorite was originally blown off the surface of Mars by another large meteorite collision. It became famous when Dr. David McKay from NASA claimed in 1996 that it contained microfossils of tiny bugs showing life on early Mars, but not everyone if convinced about that. The other view is that life is so implausibly and fantastically complicated that it shows someone, like God, must have been involved.
“Could that be true?”
It all comes down to what you believe. Any of the possible explanations of where life came from needs a leap faith, so at the end of the day it depends which way you want to jump.
“Couldn't it be proved one way or another?”
Well logically there are only two ways of proving it. Finding God and asking him or showing that life really can be created out of a soup of simple chemicals that can be found in space or on planets. Back in 1953 Stanley Miller and Harold Urey showed that these important amino acid molecules might have been made here on Earth. They passed lightning through a mixture of gases that were probably around when the Earth was formed- methane, ammonia and hydrogen. The same gases that are found on lots of planets in the solar system. They showed that the simple building blocks of life could be formed in a single week– amino acids, sugars even the building blocks of DNA. It is a long way from building blocks to people but a billion years is lot longer than a week.
“So going back to my question of how life started.”
To be truthful, I don't know.
“Finally I've got you on something.”
True but to be fair I’m a physicist not a biologist and I am dead, so you have to give me a little credit for that.
This is the story of a great journey that started with a great thought. One day in 1895 a boy looked into a mirror and wondered what the universe would look like if he could travel on a beam of light. That sixteen year old boy was Albert Einstein and that one thought started him on the road to discover his Theory of Relativity. The great man has been reinvented as Albert 2.0 to come back and blog about a journey through space on a beam of light and explain the science behind everything from atoms, blackholes to global warming. If you've just joined and want to start at the beginning use the index on the left. If you're bored try these links below just for fun.
UNSCRAMBLE EINSTEIN'S BRAIN
PRACTISE SAVING THE WORLD FROM ASTEROIDS
ALIEN CONTACT CALCULATOR
HEAR THE REAL EINSTEIN TALK ABOUT E=Mc2.
Saturday, September 22, 2007
“So where did all this life come from?”