For more on this see The Greenwich Tales.
Oldest known rock about million B. These dates may be as much as ten per cent. That is to say, 60, years ago our ancestors were mammals, probably not unlike lemurs, , years ago amphibians somewhat resembling newts or mud-puppies, and , years ago very primitive fish, combining some of the Injection mould thesis of sharks and lampreys.
The origin of life on our planet was probably over a thousand million years ago, so that the record furnished by fossils only refers to half—perhaps much less than half of the time during which life has existed.
If all the lead in our planet is of radio-active origin, which is rather unlikely, it can hardly be more than eight thousand million years old.
Astronomical evidence points to a somewhat smaller age. As the earth goes round, the moon, and to a lesser extent the sun, raise tides in the sea.
The moon thus acts as a brake on the earth, and by so doing is pushed onwards in its orbit, and moves further away. If we calculate backwards instead of forwards we find both the day and the month becoming shorter, until at a sufficiently early date they possessed the same length of about four hours, and the moon was so near to the earth as to be practically touching it.
At present the main retarding action takes place in the Bering Sea. At a geological epoch characterised by many shallow and partly land-locked seas tidal friction must have been greater Injection mould thesis now, at other times less.
So we can only say that the moon was born somewhere about four thousand million years ago, but the true figure might be as low as one thousand million, or as high as twenty thousand.
The birth of the moon was only one event in a greater catastrophe. Our sun, after a relatively brief period, probably a few thousand million years or less, of youthful exuberance as a giant star radiating energy at thousands of times its present rate, settled down as a respectable dwarf, which it now is, and has been throughout geological time.
For many thousands of millions of years it probably shone as a lonely star unaccompanied by planets. Then it appears to have passed near to another, probably heavier star, which raised tidal waves in it.
The detached crests of these waves, or one of them, formed the planets, and it is fairly clear that the moon broke off from the earth within a few years of its formation.
It can be calculated that it has not been going round the sun for more than ten or less than one thousand million years.
Various other lines of evidence converge to a date somewhere between 8,, and 1,, B. If science continues we shall arrive at the exact date in the following way. The star in question must be very far away by now. It is a wise child that knows its own father, and we shall probably not know ours for thousands, perhaps hundreds of thousands of years.
It is possible to penetrate still further into the past and to arrive at a very rough date for the origin of the sun. But any such date depends on some particular hypothesis as to the origin of stellar energy, and there are several such hypotheses, leading to very different dates.
On the other hand a number of independent arguments, based on well-ascertained facts, converge to the same date for the origin of the earth.
There are, of course, respectable scientific theories, such as the planetesimal, which lead to different conclusions. In a popular exposition it has been necessary to be dogmatic.
If I have been so it is because I consider it unlikely that any of the figures I have given will be very seriously upset in the future. In a few generations it is probable that these dates will meet with general acceptance and their meaning will gradually penetrate the human imagination.
As the earth has lasted for at least a thousand million years in a condition not very unlike the present, it will probably continue habitable for a future period of at least the same order of magnitude, possibly for very much longer.
An acceptance of such a future is bound to affect human thought. It will be realized that the things which seem to us most stable, such as human nature and the facts of geography, are really not only changeable but certain to change.
On the other hand it will be realized that remarkably little change can occur within a lifetime.
Such a world-view leaves room for optimism in the most desperate circumstances, but yet reduces the probable effects of the vastest human efforts to the tiniest dimensions.
As it is accepted, people will probably become more and more prone to devote themselves to their own affairs and those of their immediate neighbours.May 09, · Re: Injection Moulding Thesis You can find many ideas on this forum, such as % full by weight or volume.
You could research that and argue that it is supported science or dogma.
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