|March 9, 2013|
Pin the Dinosaur on the Football Field
The Solar nebula coalesced into the sun and planets about 4.6 billion years. If we were to put the geologic time line onto a football field, where would the age of dinosaurs be? Your instinct is probably wrong, but it's not all your fault. Just as the graphics representing an atom are not to scale, neither are most geologic time-scales.
First of all, let's set the scale of our football field. If we start it at 5 billion years ago, then we can include the hypothetical supernova that triggered the star formation which included the solar nebula. Each ten yard segment will be worth 500 million years and each yard will be 50 million years. The solar system will begin at the left 8 yard line and the right goal line will be the present day.
The Earth formed within about the first 20 million years and the moon within the first 100 million years and that brings us to 4.5 billion years ago, or the 10 yard line. The sun was 70% as luminous and the Earth was bombarded by left over debris, some of which, along with water vapor from volcanic outgassing, became our oceans. Carbon dioxide was another major product of volcanism, and its greenhouse effect kept Earth warm under a cooler sun.
The left 24 yard line (3.8 billion years ago) is quite an important marker. The Earth was naked in those days, unprotected from the solar wind and energetic gamma rays because the Earth's magnetic field didn't form until the 30 yard line (3.5 billion years ago). Water, hydrocarbons, radiation, and a few non-metals somehow got cooked up into a goo that became alive: Simple, one cell organisms -- prokaryotes, probably getting their energy from hydro-thermal vents and some chemistry that would be quite toxic to us.
And so life evolved for another 2 billion years as simple one celled organisms. These prokaryotes lacked a nucleus, organelles, and mitochondria. It was a cell eat cell world. Some of cells became parasitic. After being consumed, they would eat their attacker from inside out -- a good strategy unless you eat all of your attackers. Success could be a dead end. Some parasites evolved to eat their attacker without fatally damaging them right away and next thing you know -- symbiosis! Mitochondria were probably such parasites in the beginning. And now they are the powerhouse in almost every eukaryotic cell -- a whole new life paradigm that didn't arise until the right side 36 yard line (1.8 billion years ago). Complex cells, which form the basis of every higher and multi-cellular organism, have been with us less than half the time there has been life on Earth.
About 580 to 530 million years ago (the right side 11 to 10 yard line) came the Cambrian explosion and the first worms, molusks, and insects. Oxygen levels went up and an ozone layer formed to block damaging UV light from the sun. Things started crawling out of the ocean to live and grow on dry land by the 8 yard line, fish and reptiles arrive at the 6 yard line. The earliest dinosars show up at the 4 and 1/2 yard line. They (except for birds) died out at 1 yard and 1 foot ago when a little meteorite struck the Yucatan at 120,000 miles per hours and spread a nice even layer of iridium around the world. Is that where you would have instinctively placed dinosaurs on our timeline?? Hominids don't make an appearance until 4 centimeters ago. Written human history spans the last one tenth of a millimeter. A human life time is about one tenth of a hair's breadth.
The sun will continue for another football field, growing in radius and getting brighter, then become in turn a red giant and white dwarf. We should be OK for about another 20 yards and then we'll need to look for other places to live. A nice stable red dwarf with planets would be a good choice. If you'll recall a previous post The Color of Stars, some of those have 10 to 20 football fields to go on the main sequence.