In the pre-biotic Earth the solar system originated around 4. The energy for forming the molecules was provided by lightning, volcanic activity, meteorite bombardment, high temperatures due to greenhouse gasses and UV radiation. At first, the Earth was cold and later melted from heat produced by compaction, radioactive decay and the impact of meteorites. The molten material sorted into layers of varying density with the least dense material solidified into a thin crust. The present continents are attached to plates of crust that float on the mantle.
The first seas formed from rain that began when Earth had cooled enough for water in the atmosphere to condense. The prebiotic era dates from 4. The earliest life known is dated to 3. They simulated conditions on the early Earth by constructing an apparatus that contained a warmed flask of water simulating the primeval sea and an atmosphere of water, hydrogen gas, CH4 methane , and NH3 ammonia.
Sparks were discharged in the synthetic atmosphere to mimic lightning. A water was boiled while a condenser cooled the atmosphere, raining water and any dissolved compounds back to the miniature sea. The simulated environment produced many types of amino acids and other organic molecules leading them to conclude the prebiotic synthesis of organic molecules was possible.
However, the question of the concentration of methane and other chemicals is in doubt so the applicability of the results is uncertain. Polymers are chains of similar building blocks or monomers, synthesized by condensation reactions H and OH are removed from polymers and H20 is produced.
Early polymerization reactions must have occurred without the help of enzymes. Clay increases the rate of polymerization in these ways: Monomers bind to charged sites between close clay layers, concentrating amino acids and other monomers Metal ions at binding sites in clay catalyze dehydration reactions The clays provide more stable conditions for the formation of molecules. Functions of RNA in polymerization: There is a type of RNA called a ribozyme that can catalyze its own replication.
Protobionts, or aggregates of abiotically produced molecules, accumulate organic materials like polypeptides from the environment. However, they probably do not possess a mechanism for replicating their particular characteristics so life cannot start.
However, an information storage mechanism like RNA would allow them to pass on their characteristics. Short strands of RNA, perhaps most importantly the RNA called ribozymes, could have copied themselves and could have catalysed other reactions. They could then align nucleotides according to a certain pattern when bound to clay. Thus RNA could be replicated and passed on. This is supported by the fact that RNA plays an important role in genetic control in cell life today.
Living cells may have been preceded by protobionts, aggregates groups of abiotically produced molecules. To form life they need to compartmentalise themselves from the surrounding water. Some protobionts in the presence of lipids form a molecular bilayer liposome around the protobiont droplet when shaken. This resembles the lipid bilayer of modern cells.
The liposomes can break, reform and merge with others and mix their contents. Within these droplets reactions could be catalysed and RNA could replicate itself. The most successful liposomes at surviving would pass on their characteristics and develop into early prokaryotes.
Eukaryotic cells were probably symbiotic groupings of prokaryotic cells with smaller species living within larger prokaryotes. The endosymbiotic theory focuses on the origins of chloroplasts and mitochondria. The ancestors of these organisms photosynthetic prokaryotes like algae or respiring bacteria originally entered the host cell as undigested prey or internal parasites.
Normally the invaders would be digested but in this case they were not. The host cell would allow them to live and exploit these orginisms provide food and energy. Those which absorbed prokaryotes which became chloroplast and mitochdria formed plants, those without the chloroplasts became animal cells. The evidence that supports this theory is: Mitochondria and chloroplasts have bacteria-like RNA and ribosomes 70S as opposed to 80S in eukaryote cytoplasms that enable them to make their own proteins and divide independently of the host cell.
Mitochondria and chloroplasts both have double membranes, the inner one probably that of the original cell, and the outer that which was created when the cell was absorbed. Thylakoids resemble structures found in blue-green bacteria. Chloroplasts and mitochondria have naked DNA like prokaryotes.
Chlorophyll a is found in both prokaryotes and eukaryotes. Christae in mitochondria resemble mesosomes in bacteria. Lamarcks theory of inheritance of acquired characteristics states that the modifications an organism acquired during its lifetime could be passed along to its offspring.
The common idea is that if a giraffe stretches up to reach high leaves, it can pass a long neck onto its offspring. There is no evidence that acquired characteristics can be inherited. Characteristics that can be passed on are in your genes. If you are not born with genes programming for certain characteristics, you cannot pass down characteristics acquired during your lifetime as these characteristics do not reach sex cells.
Populations tend to produce more offspring than an environment can support but populations tend to remain constant There is a struggle for survival among organisms in a species with varied characteristics Those individuals which are best adapted to their environments are most likely to survive Only these pass on their positive characteristics in the form of genes to their offspring who also survive While on his Beagle voyages, Darwin became intrigued with the different types of finches found in the Galapagos.
All the species of birds were very similar, just like a species on the mainland of South America but between the islands they differed in size and beak shape. Darwin found that the birds fed on different types of food. Their beaks were adapted to eat different types of leaves, worms and seeds and other types of diets. Darwin explained all his observations and thoughts about the origin of species by the concept of "natural selection".
This theory states that great diversity in a species ensures that some members of a population will be more suited to their environment than others. These individuals will be more likely to live long enough to reproduce and pass on their well-suited genes. Therefore, because those that are best suited the food on an island are the ones who have the most children, a population will, over time, adapt itself to its environment.
The change in the frequency of characteristics genes in a population with a common gene pool is evolution. Panspermia is the theory which suggests that life arose elsewhere in the universe and travelled to Earth through space in comets or meteors.
Special creation states that a creator s formed life directly. Panspermia - Organic compounds and amino acids have been recovered from modern meteorites. This theory is not incompatible with evolution, which would have occurred once life reached Earth. The theory could be tested in the future by looking for life similar to our own beyond Earth but space travel is not yet sufficiently developed.
Special Creation - most of the evidence for this theory is found in religious faith. There is no real scientific evidence for this theory other than a lack of evidence for alternate theories. The theory cannot be falsified contradicted by observations, unlike evolution and panspermia. However, some believe that more and more evidence is being found that points towards creation by a divine being. The Lamarckian theory also lacks any evidence in its favour.
Evolution fits with commonly held facts and is supported with sufficient amounts of evidence discussed in D. It operates based on well understood processes and laws of nature that have not been contradicted by any current observations, and thus is the preferred theory. The two northern continents are only separated by a small sea, the Bering Straight which has been crossable at times in the past.
They have very similar mammal life. The three southern continents have been far more isolated from one another and show far greater variety of mammal life. Looking at the way in which continents have drifted over time and examining the fossils in them we can map out the development of different sorts of mammals. Monotremes and marsupials developed in Gondwanaland mya before the three southern continents were separated.
Placental mammals developed life young developed later mya and replaced almost all of the monotremes egg laying mammals and marsupials undeveloped young born into pouches in the other continents. Australia was separated from the other continents so animals there could no longer mate with animals from other continents and Australian animals could not travel elsewhere.
This is why marsupials and monotremes are now found only on Australia. Monotremes and marsupials have evolved to fit the niches within the Australian environment and there are no placental mammals. This is simply because of geography not because Australia is unfit for placental mammals. These observations and other similar examples are expected under the theory of evolution. Study of past evolution - phylogeny Sand eroded from the land is first carried by rivers, seas, swamps where the particles settle to the bottom.
These deposits pile up and compress the older sediments into rock. Dead organisms are swept into seas and swamps then settle to the bottom with the sediments. When the sediments turn to rock under pressure the hard parts of the animal may remain as fossils. Minerals also leach into the soft parts of the organism, leaving a petrified cast of its shape within the rock. Fossils can also be stored in: Resins, which become amber Frozen in ice or snow In acid peat in which they cannot decay D.
Fossils contain isotopes of elements that accumulated in the living organisms. If the isotopes are unstable, they will lose protons and break down over time. Since each radioactive isotope has a fixed half-life it can be used to date fossils based on the relative concentrations of the reactant and product of the decay.
Half life is the amount of time it takes for half of a sample of a certain substance to break down. Carbon has a half life of years so useful or dating fossils less than , years old. Potassium has a half-life of 1. Look on the graph at how many times the concentration of the original isotope has halved then multiply that by the half-life.
The existence of the many fossils similar but different to current species is expected under evolution. The Acanthostega fossil shows an amphibian from mya which has eight fingers and seven toes so is different from current organisms.