I am referring to abiogenesis - life arising from non-life matter. Cacti have not appeared out of simple chemicals, they have evolved from other plant-based lifeforms (in fact, there is no "first cactus").
My point is that, despite the huge abundance of life on Earth today, it is all based on a very old abiogenesis event, with all indications that it was more or less a singular event.
All life on earth seems to be part of the same philogenetic tree, so it seems that life appeared once and then kept evolving from that initial life-form. Of course, there is a good chance that there was some variety of initial organisms that either merged together in symbiotic relationships, such as mitochondria with the rest of the cell, or got out-competed by the one type of organism that we are all descended from. This still indicates that life arose in a single place and only over a relatively short amount of time.
My point is that, despite the huge abundance of life on Earth today, it is all based on a very old abiogenesis event, with all indications that it was more or less a singular event.
All life on earth seems to be part of the same philogenetic tree, so it seems that life appeared once and then kept evolving from that initial life-form. Of course, there is a good chance that there was some variety of initial organisms that either merged together in symbiotic relationships, such as mitochondria with the rest of the cell, or got out-competed by the one type of organism that we are all descended from. This still indicates that life arose in a single place and only over a relatively short amount of time.