Life on Earth  

Big Bang ? Universe starts from nothing or almost nothing some 12 - 18 billion years ago and expands. Flying debris and gases from the explosion start to form the solar systems and planets. Planet Earth solidifies 4.6 billion years ago but is barren and void of any life whatsoever. But then somehow, Life is thought to have originated one billion year later through a system of self- replication occurring in some micro-something with the help of an external energy source. Continuing on, we will base our further speculations on the theory of evolution and natural selection and ignore other views.

Therefore, those something, which self-replicated the best by using this energy most efficiently, evolved later into simple cells with a  separating cell-wall. Those so-called Prokaryotes are the bacterias which were for the next 2 billion years the only life on earth. Some of them, the photosynthesizing bacterias were also important as they enriched the atmosphere with oxigen. Till then only anaerobic life existed. Another important step in the evolution of life was the appearance of cells with an enclosed nucleus. Those eukaryotic cells evolved probably from forming symbiotic relationships (by invading themselves?) of procarytic cells. The Protists are still single cells and another important evolutionary step was the appearance of multi-cellular structures. The first multi-celled life beings were soft bodied marine invertebrates and came into being some 700 million years ago. Life for a long time afterwards only existed in the water, with the land being completely barren. Invertebrates called trilobites abounded in the oceans and later the first vertebrates (another significant evolutionatryadaption) some simple fish appeared.

450 million years ago the first vascular plants ventured onto land to be the first land based life form and amphibians evolving from fish followed around 150 million years later to claim that distinction for the animals. Some amphibians, which became to depend less and less on water, branched later into reptiles, which were the first true land animals. Reptilian creatures with the mighty dinosaurs were dominant till the mass extinction 65 million years ago, with only a few of them surviving it. Some reptilian ancestors of birds and mammals somehow took this catastrophe better and evolved into today's true birds and mammals. Humans as known today, are very late arrivals in this world venturing out of Africa some 80 000 years ago but are now the most dominant beings and so successful, that many other life forms have to yield to them.

Life Classification


Aristotle, the great Greek philosopher, established a 2 Kingdom system with Animals and Plants, which actually would be good enough for us as we mainly deal with those two life forms here but for good science's sake let's present the 5 Kingdoms as established today.

All together 1.4 million species of life forms on earth are known and classified but the total estimate goes anywhere from 5 to 30 million species (very exact numbers, aren't they?).

People, who are not so much interested in explications but like to see and enjoy pictures of animals and plants, should check out the nature section of our visual companion site called Ecuador-Images.net.