Evolution and the Origin of Life 1
Life on Earth Life on Earth goes back billions of years but how long ago did the first humans appear? Humans (Homo sapiens) have really only been around for about 195 000 years This may seem like a long time when we consider the average human lifespan but in geological terms, this barely registers on the scale 2
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Life on Earth We re going to take a look at the major stages of life on Earth. What conditions made it possible for life to evolve? How did life evolve? How can we know that there were other species that existed that we don t see anywhere today? 4
FORMATION OF THE EARTH 5
Before Life on Earth Recall sec 2: Roughly 4.6 billion years ago, our solar system was created from great big cloud of dust and gas Through gravitational pull, all this dust and gas was pulled together and formed the sun! From there, matter was expelled around and this then condensed and was pulled together to form each of our 8 planets (sorry Pluto ) 6
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Before Life on Earth Recall sec 1& 2: Over time, the Earth cooled, creating the three main layers of our planet: the core, the mantle and the crust 8
Before Life on Earth At this time, there was still a lot of debris flying around in space around the Earth and much of collided with our planet But this all seemed to stop about 3.9 billion years ago This is lack of meteorite bombardments is one of the key factors that allowed life to emerge 9
Conditions for Life on Earth When did life first arise on Earth? It is believed that life would have arisen on Earth between 3.5 and 3.8 billion years ago How do we know? The oldest fossil that has been found so far has been dated at being 3.5 billion years old. 10
Conditions for Life on Earth But what were the conditions needed for life to arise? Well for life to be possible, it means that complex molecules were needed and of course water In order for complex molecules to arise, you need energy to help simple molecule reorganize And these have to be the right molecules! And of course, all of this takes a loooooooooong time. 11
Conditions for Life on Earth Conditions for life to arise: 1) Presence of essential chemicals These were present in the atmosphere and also thanks to volcanic eruptions 2) Presence of an energy source UV rays from the sun, lightning, heat from volcanoes 3) Presence of liquid water Water is a key element in many chemical reactions 4) Long period of time Needed to produce the right mix of molecules and since this occurs pretty much randomly, this process took time 12
HOW DO WE EVEN KNOW THERE WERE OTHER LIFE FORMS THAN WHAT WE SEE TODAY? Fossils! 13
Fossils What is a fossil? The remains or traces of an organism that has been preserved for a very long period of time in the Earth s crust Usually when an organism dies its remains will just decompose, but sometimes the conditions are just right so that the remain actually get preserved inside the Earth s crust Thanks to carbon dating, we can determine the age of these fossils and therefore reconstruct the history of life on Earth 14
Fossils How are fossils formed? Generally speaking fossils are found in sedimentary rock Review sec 2: sedimentary rock is formed when there is an accumulation of sediment (solid particles) that eventually compresses and hardens over time 15
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Fossils How can we tell how old they are? In addition to carbon dating (a form of absolute dating) that allows us to determine exactly how old a fossil is, paleontologist's also use relative dating Relative dating is a method that allows us to establish the general order in which fossils formed; in other words, we can determine which fossils were formed first but not their exact age 17
Fossils How can we tell how old they are? To do this we use stratigraphic layers Sedimentary rock is formed in layers, with newer layers constantly being formed on top of the old as more sediment accumulates How is this useful? We know that anything found in the same layer must be the same age (Law of original continuity) The deeper the layer, the older it is since new layers always form on top (Law of superposition) 18
Which one is older: the pottery or the stone wall? 19