L is for life. Not just life but carbon-based life, this is the only way life on Earth seems to exist, maybe there is some bacterial with no need for carbon.

        But I do not know of any life on the planet that can survive, without carbon. At the beginning of life on this planet, carbon was, simply put, the only option life had a chance to start with, and where is all of that carbon now? Turned into mountains, caves, or buried deep under seas and oceans, no longer available for life to make use of. Every year prior to mankind's arrival as a species (that does not so much live with the planet, as it adapts the planet for our needs) the planet has lost access to around 10 gigatonnes of carbon every year, year in and year out and in the early day's of life on the planet, this amount was quite a bit higher. However, the planet's interior was quite a bit more active than it is today, but because of the slowly cooling down, that comes with time and the slow decaying of elements that normally produce heat as they decay, the tectonic plate actively has decreased. Try and tell someone who was in a large earthquake or volcanic event, that they were lucky that they were not on the planet a billion years ago, but prepared to duck, as they either take a swing at you or throw a part of the house that tried to kill them at you!                                                             100,000,000 gigatonnes of past life are now tucked away from life's ability to use any of that carbon unless it comes in contact with those still actives parts of the planet that return that carbon back into the atmosphere as carbon dioxide as the material is melted and then changed into a gas at such places. This amount is calculated to be around 3 gigatonnes on average each year!                                                                      Scientists will tell you that, the planet is the most perfect recycler of life that has ever been produced, and they are correct, but even the best recycler ever designed will constantly miss a little bit and after 3,000,000,000 years of this tiny amount every year (as if 10 gigatonnes sequestrated and 3 gigatonnes returned each year is a tiny amount, but this is all relative to how much carbon there was at the beginning of the start of life) There will come a time when the loss of enough carbon from the carbon cycle will start affecting how life on the planet can continue, and for this planet, the examples of this happening can be seen to all the way back hundreds of millions of years ago. Life and it need to adapt to ever so slowly changing atmospheric conditions both in the strength of the sun's energy that reaches our planet and the make-up of the gases, all produce changes in what types of life can be cultivated. Plantlife that existed when dinosaurs roamed this planet, could no longer survive the much lower levels of carbon dioxide in the atmosphere that is now available.                                                                                                                                                           Starting around 2.5 million years ago the ice-ages began because the levels of carbon dioxide were low enough to cool the planet where ice could now be staged on the planet in ever-increasing amounts. As the production of ice on the planet started lowering the carbon dioxide-rich oceans of the planet this evaporation allowed the atmosphere to slowly increase its levels of carbon dioxide, and after many thousands of years, the balance between warm and cold tipped in favor of a warmer interglacial period that would only last until carbon sequestration again reduce the levels of carbon dioxide in the atmosphere low enough to repeat the cycle. During these last 2.5 million years the planet would have sequestered 2.5 x 7= 17.5 million gigatonnes of carbon and the only place on Earth that is large enough to contain that much available carbon was the great oceans of the planet.                                                                                                    Now there is estimated to be only around 40,000 gigatonnes of carbon dioxide left in these great oceans, not nearly enough to bring the planet out of another cycle of ice bringing staged on the planet if mankind would no longer be a viable species on the planet, which has been what has kept the planet from entering into another cycle that should have begun starting around 3,000 years ago!                                                 To me who has studied the past iceages for over 50 years, everything fell into place with the coming of the drilled ice-cores that we now have access to that information starting around 10 years ago. Such a huge amount of data that both offered a glimpse into the past rise and fall of carbon dioxide in the atmosphere during period of glaciers and inter-glacier time frames, so tightly in-line with increasing and decreaseing levels of carbon dioxide in the atmosphere! The only response that mankind can make that will both maintain the amount of ice being staged on the planet and reducing the temperatures extremes that has lead to weather extremes, is to use all of the available fresh water of the planet to regrow and rebuild all of the arid and semi-arid areas of the planet, to increase cloud cover enough to offset all of the other negative aspects of a planet with too much uncovered soils and too little cloud cover. Dan