Wednesday, September 17, 2008

The Journey of Life Part 1 (Life begins on Earth.)

Scientists have proven that the Earth was formed about four and a half billion years ago.

The formation of the Earth was called the Hadean Era - after 'Hades,' the mythical Greek version of Hell. This was because the Earth resembled Hell - with surface temperatures of 230°C. Even as early as then, however, scientists know that Earth had liquid water oceans.

Scientists know how old the Earth was and what it was like in the beginning because of zircon crystals discovered in Greenland. They date back 4.4 billion years and could only have been formed under certain geological conditions.

This was followed by the Archean Eon, when the Earth as we know it today was formed. There is plenty of evidence about this era, as rock formations have been discovered in Greenland, Canada, Scotland and India that date back this far.

The Archean Eon was when life appeared on Earth. Interestingly, it was also a period in which lots of extrasolar debris struck the Earth. Some people have suggested that life on Earth was carried there by a asteroid or meteorite. Others hypothesis like life started with protobionts.

Protobionts are organic molecules surrounded by a membrane. They're not life, exactly, but they mimic many of the properties of life - like being able to reproduce and react to their environment. Most importantly, Cornell University proved that in an environment like Archean Eon Earth, they could have formed spontaneously.

Over the course of 400 million years, protobionts evolved into prokaryotes - bacteria and archeaea. Basically, the first form of life on Earth. We know projaryotes existed on Earth at this time because we have fossils of them dating back three and a half million years.

Now to accept protobionts became prokaryotes, you have to accept that very primitive forms of life are capable of evolution.

Fortunately, that's been proven by scientist Richard Lenski. He took a very simple Escherichia coli bacteria and, in his lab, proved that bacteria is capable of evolutionary adaptions in order to react better to their environment.

Basically, in order to better suit their environment, bacteria adapt and become different. In Lenski's experiment, a culture of bacteria that learned to feed off citrate (which E. coli normally can't) enjoyed a population explosion. In keeping with Darwin's theory of natural selection, had this occurred 'in the wild,' the E. coli that had adapted would have had a distinct advantage over the unadapted bacteria.

The same proof exists in most British hospitals - Staphylococcus aureus bacteria has evolved to become resistant to antibiotics. Because antibiotics kill the non-resistant Staphylococcus aureus, Darwin's theory of 'survival of the fittest' explains the success of antibiotic resistant bacteria, the famous Methicillin-resistant Staphylococcus aureus or MRSA bacteria.

Just like the bacteria we witness evolving today, prokaryotes thrived on Earth during the Archean Eon. As E. coli and Staphylococcus aureus prove, prokaryotes still exist today.

Prokaryotes were one path of evolution. The other path, which separated at this point, were eukaryotes. Whereas prokaryotes were single cell organisms, eukaryotes had more than one cell. They're what would evolve into plants and animals - basically, anything that isn't a bacteria.

The earliest fossils of eukaryotes date back over a billion years. They show that eukaryotes were very similar to prokaryotes. In fact, it was like two prokaryote cells decided to occupy the same membrane and exist in a symbiotic relationship.

Now exactly HOW this leap occurred is open to discussion. Was it a mutation? Perhaps a prokaryote divided itself to reproduce, but the cell division failed and created a 'Siamese' bacteria - one that flourished! However it worked, it worked.

We have fossils that show the arrival of a new form of life that was remarkably closely linked to the form of life that had existed before it. One form of life evolved into another and we have the fossils to prove it!

The next stage of the Earth's development was the Proterozoic Eon, starting about two and a half billion years ago and finishing about a billion years ago.

Life during the Proterozoic Eon consisted of single celled organisms (the bacteria) and the new multi-cellular organisms. Oxygen started to fill Earth's atmosphere (we know from all the geographical evidence) which caused a lot of changes for life on Earth. Oxygen was poisonous to a lot of the existing life forms and a lot of them were wiped out. 'Survival of the fittest' saw the ones that could cope with oxygen flourish.

During this period, hundreds of different fossils were left for us to discover, which neatly illustrated the development of eukaryotes. Fossils exist showing the development of simple multi-cellular organisms into more complex forms of life, like algae, plants, and 'bags.'

We know that this process was evolution because of the fossil trail. The eukaryotes might have become more complex, but they didn't just spontaneously turn from one form into another. The links between the original form and what they evolved into are quite obvious, like fingerprints.




The next stage on Earth was the Palaeozoic Era, which began about 550 million years ago. This was the era that saw life on Earth explode with diversity. It's this stage which makes people query evolution. After all, in four billion years, evolution developed nothing more sophisticated than multi-celled plants and algae. Suddenly, everything would change over the course of a (relatively) short space of time!

But I'll get to that later. The important things to take away from this first of my posts on evolution are:

  1. We can prove the Earth is four and a half billion years old.
  2. We can prove that life (in the form of bacteria) existed three and a half million years ago.
  3. Fossils prove that single-celled creatures evolved/mutated into multi-celled creatures over a billion years ago.
  4. Fossils prove that a wide diversity of simple life forms, all with similar roots to the first multi-celled organisms, existed on earth almost a billion years ago.

Next time, I'll take you on the journey that sees a few multi-celled algae and 'bags' become dinosaurs and people...

To Be Continued...

3 comments:

Kitty said...

Sometimes, reading your blog makes my brain hurt. :-p x

Eddie said...

Unfortunately even a mountain of evidence so intracontravertable it's not funny can simply be waved away when it doesn't support the desired agenda.

Confirmation bias can be as overwhelming as the evidence :)

sad times we live in when evolution is even in the slightest doubt. But when you need a god you'll do anything to provide a home for one. intelligent design springs to mind.

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