A good place to start

Life on earth started slowly, gathering speed and complexity over a very long time. Conditions do not sound too positive for nascent life forms around the time when the earth was formed about 4,5 thousand million years ago. Bear in mind that oxygen arrived so much later and the earth’s surface only became solid around three thousand nine hundred million years ago.

Things started happening within the “short” spell of fifty million years after that, although there is a theory that complex organic molecules, necessary for the beginnings of life, had already formed in the protoplanetary disk of cosmic dust grains before the earth was properly formed.

The moon is thought to have formed in response to a collision between earth and an hypothesized planet called Theia. This sent a very large number of small “moonlets” into orbit around the young earth. These bits and pieces gradually coalesced into the single moon that provided the gravitational pull for stabilising the Earths fluctuating axis of rotation, bringing about the seasons and giving the sea its tides.

Primitive life, single cells called prokaryotes were present on earth within one thousand million years of the earth becoming a planet. By three thousand million years ago photosynthesising bacteria began to produce oxygen on earth that made plant and animal life possible, but poisoning some of the older bacteria that had been thriving here for many millions of years. At this time the moon was still so close to the earth that some tides were around 300 m high. Frequent hurricanes swept land and sea.

The way was "paved" for the mass oxygenation that came around 500 million years later, taking until 1800 million years ago before sufficient oxygen brought about the advent of the eukaryotes, organisms with cells containing a nucleus and other organelles, all enclosed within membranes.

By 1200 million years ago meiosis and sexual reproduction were present in single-celled eukaryotes. The first protozoa, single-celled organisms with animal-like behaviour, such as motility (active and spontaneous movement from own energy) and predation (preying or feeding on other living things), appeared only around 750 million years ago. The ozone layer, caused by the accumulation of atmospheric oxygen, formed around the earth about 600 million years ago.

The first primitive land plants evolved from green algae along the edges of lakes around 434 million years ago, probably accompanied by fungi, which may have aided them through symbiosis. The first signs of teeth in fish appeared around 410 million years ago, the first dinosaurs around 225 million years ago, as did the first mammals. By this time the cycads and conifer trees were diversifying.

Archaeopteryx, thought by some to be the first dinosaur ancestor of the birds, appeared around 155 million years ago, at the time when the earth also welcomed its first blood-sucking insects. Only after dinosaurs became extinct around 65 million years ago did the birds really take over the skies in a big way.

The first proliferation of flowering plants on earth came at about 130 million years ago, i.e. the earth has seen flowers for less than 3 percent of its existence. Bees to pollinate them came only a 100 million years ago and ants have been around for the last 80 million years.

People? Living on earth for less than 0,04 percent of the span of existence of their planet, but contributing more to destruction of fellow species and despoiling of nature overall than anything else ever alive (Bryson, 2005; Collis, 1950; Wikipedia).