Majisha wrote: nash1429 wrote:
4:26 "Surface area grows faster than volume."
It's still a somewhat entertaining video, if factually lacking. And I don't see a problem with focusing on arguing against creationism. The music was pretty epic, too.
Well, understand that they tried to fit it all into a 10:00 video meant for people who knows very little of actual biology. Like me!
There's nothing wrong with simplifying and breaking things down into easy to understand terms for the layman who doesn't know a lot of biology, but that's no reason to be inaccurate. Of course, I probably shouldn't criticize too much unless I've tried it myself, so here's an attempt to summarize the papers I cited in more layman's terms (please excuse anthropomorphic terms -- I'm pretty sure we all accept that molecules don't "want", "need", "invent", "figure out", etc... but these are useful metaphors for getting the idea across, especially when contracting hundreds of millions of years of chemical reactions into a few minutes of brief history):
1.) A few hundred million years after the Earth first formed, the surface had cooled enough to support being covered with water. Evidence suggests that early Earth at this time was completely covered in water. It had an atmosphere high in carbon dioxide, which in turn made the oceans very acidic (remember: the difference between acid and alkaline is how much hydrogen (as protons) there is in the solution; acid = a lot of hydrogen, alkaline = a very little hydrogen).
2.) Ocean water can circulate through the crust, entering in some areas and flowing slowly through the rock, heating up, and reacting with chemicals in the rocks. This removes the acid from the water as it flows through, and allows a number of simple molecules like carbon monoxide, ammonia, methane, phosphates, sulfates, etc. to form. This water circulates back into the ocean at "hydrothermal vents". Some of these vents are extremely hot, and while life may have found a way to live there now, were probably too hot for life to form. Others are much milder with temperatures not so different from what modern life is most comfortable at.
3.) The rocks at these vents can be rather porous (full of small holes and compartments). The rocks are rich in iron, nickel, and sulfur, which are important elements in life for helping life reactions happen. Warm alkaline vent water flows through these tiny (even the size of cells in modern life) compartments, mixing with the cold acid sea water. This sets up some important conditions. Warm tends to rise and cold tends to sink, so the temperature difference sets up small circular currents through the compartments in these rocks. As this "convection current" flows, it serves to concentrate larger molecules in the compartments (if there were no compartments, molecules from the vents would just dilute into the sea and never react with each other). Also, difference between warm and cold can act as a source of energy. More importantly, the difference between acid sea water and alkaline vent water means that the hydrogen will flow from high concentration to low concentration, which also can act as a source of energy. There is also an electrical gradient in the rocks due to the difference in sea water and vent water when they mix. This is also a source of energy.
4.) This sets the stage for the reactions that lead to life to begin. The simple carbon, nitrogen, and sulfur molecules in the vent water will start reacting with each other using the energy in the vent system. They will start to form simple versions of the important molecules to life, a.k.a. biomolecules: simple sugars, amino acids, nitrogenous bases (which will later become the nucleic acids), etc. These larger molecules get concentrated by the flow through the compartments, and continue to react with each other. Some may build up into larger complex molecules while others are broken down and re-formed into different molecules. New molecules are always being added from the constant flow of the vent water, and there is always energy available from the differences between the vent water and the sea water. Sugars may get together and form chains, or larger sugars. A few amino acids may get together and form simple proteins, which may or may not have some functions as they float around the compartments or stick to the compartment walls. A sugar, phosphate, and nitrogenous base get together to form the first nucleic acid: RNA. Single RNA units get linked together and form chains. And so on, always building up from the constant supply of energy and raw materials. However, this is just very complex geochemistry, not life.
5.) After millions of year of this, one of the most world-changing things in the history of the Earth happens. A molecule in these compartments, probably an RNA chain, starts to copy itself, using the materials available. RNA has been known to do this, and self-copying RNA has been made in the laboratory. If humans can do it in the lab after only a few decades of study, imagine what nature can do with perhaps a hundred million years and a practically unending supply of raw material. This RNA making copies of itself is the "replicator". It is not perfect, and it makes mistakes. Not all of its copies are exact. Some of them are better at copying themselves. Some of them are worse. The only constant is that all of them need materials to copy themselves.
6.) This is the beginning of evolution by natural selection. Imperfect copies passing on their traits to their copies all competing for resources in the environment. May the best copies win. Nothing breeds invention like necessity and competition for survival. If you have the better copying strategy, then your copies will expand and spread out. If you have a worse strategy, you may be too slow to get the resources you need to make copies, and eventually you disappear (become extinct). If you can figure out a way of making use of the hard work of other replicators, say by breaking them down and using their parts, then you may have an advantage. If, instead, you cooperate with other replicators so that all of your copying gets better, you may have a different advantage. Some replicators may continue building from raw materials, others may act like predators breaking others down, and still others make cooperate and become bigger, better, and stronger than their rivals. This is the nature of pre-life in the "RNA world".
7.) After millions of years of this kind of competition, a lot of things can happen. These RNA replicators may develop many strategies for offense and defense as they flow through their microscopic compartments in the rocks of the vent. Some may start working with amino acids to help make their copying reactions faster. As certain amino acids associate with certain bits of RNA, the beginnings of the genetic code are born. Other RNAs which are good at attaching amino acids to each other may start working with those to build new useful molecules which help them accomplish their copying better than others: these new molecules are proteins. Some may simply form repeating structures of sheets which RNAs may use for protection from other RNAs that would break them down (this is similar to how modern viruses are). Some may find certain proteins can help make the RNA more stable and aid directly in replicating it. If RNA can delegate replicating from itself to a protein, this may be more efficient and therefore be an advantage. We are now in a microscopic chemical world of RNA and Protein together in the competition for best RNA replicators. Cooperation between units of RNA (genes, in a sense) make bigger replicators, but all aspects of offense and defense, breaking down food or building up from resources, etc. are now on a single large molecule, so this may be a big advantage. Scientists sometimes call this stage the "RNP world" for RNA and Proteins working together.
8.) Over the course of RNP world, something interesting and important starts happening. Proteins coded by the RNA take over more and more of the functions of replicating, protecting, maintaining, and providing energy for the RNA, and the RNA replicators become more like information storage molecules than being active in their own replication. However, RNA tends to be less stable and more vulnerable to attack than another up and coming nucleic acid: DNA. DNA has mostly the same bases and structure as RNA (to be specific, each unit of DNA has one less oxygen than the corresponding RNA, hence the name "D
cid"). DNA, however, has a tendency to form a very stable double-stranded molecule. At first, RNA only keeps some parts of it copied into DNA, but over time DNA becomes the master copy of all of the information necessary to replicate the molecule. DNA by itself is not a replicator, but all of the machinery is in place for it to take over. RNA gets "demoted" into being a messenger molecule between the master copy and the machinery to build proteins for the sake of the master copy.
9.) Is this life? Well, it is at least getting very close. The reactions taking place in these compartments at this stage may seem very similar to the life reactions going on inside a modern bacterium. The key difference is that the bacterium is a free-living lifeform, while back in our vent system of long ago, all of this biochemistry is trapped inside of compartments in the rock. Any compartments closer to the ocean side which erode away lose all of their contents to the surrounding ocean, so whatever "life" may have been occurring in them dies.
Clearly something needs to change to give an advantage. There would be a strong advantage in not dying when your compartment wears away. If only you could have a compartment of your own.
10.) Which brings us to the next big step in the early evolution of life, which leads us to free-living cells. To this point, everything happening in the compartments is serving the replicators. It is likely that replicators are sharing their genes among the entire system, as bits move between compartments (just like they do in modern bacteria, transferring things like antibiotic resistance between each other). However, other types of reactions are happening in the compartments. Some molecules are being broken down for energy for replicating or maintainance. Other molecules are being built up for storing energy and providing structure. Among these are lipids (fats, waxes, cholesterol, oils, etc.), and at one point a very important kind of lipid is formed: the phospholipid. If you could see a phosopholipid, it might resemble a head area with two tails. The "head" likes water, and the "tails" do not, so when they are in a solution, in interesting thing happens. The tails will face away from the water (and in the case of our ancient compartments, towards the rock walls of the compartments), while the heads will face towards the water. So, as phospholipids start to form, they quickly line the walls of the compartment, forming the first membranes. Any proteins attached to the wall, perhaps as an anchor, or perhaps as a tunnel to the next compartment, will get stuck in the membrane. As life goes on and that compartment starts to wear down and be exposed to the ocean, any phospholipids will now form another layer on the outside as their "tails" try to get away from the water. Viola! Cells with membranes, free to live and grow in the sea on the rocky surface of the vent.
11.) There was probably a lot of trial and error and a lot of false starts for this early life, but while it was near the vent, it had abundant resources with which to grow and spread (and die). After hundreds of millions of years of this kind of thing, life was able to spread through the darkness of the sea and eventually up to the light, where a new, very abundant energy source awaited any who could evolve to take advantage of it.
And, 3.8 billion years later (after #10), here we are talking about it.
Hmmmm... So, I guess it is hard to over-simplify AND be accurate. I feel this explanation is still pretty complex.
But, well, life is a complex thing, and even the best hypotheses for its formation don't lend themselves to the most simple explanations.
Comment and critique on this are very welcome.
If anyone finds this to be a reasonable explanation and has some mad animating skills, making it into an animation to explain it would be awesome (and probably much clearer than trying to convey it in words alone). Feel free.