how old is earth? – Disease Zone

Question: how old is earth?
- Keywords:
  earth
Asked by 12swanb to Lyn, Katy, Paul, PB, Ruth on 20 Jun 2013.
- Paul Waines answered on 20 Jun 2013:
  
  The earth is a whopping 4.5 billion years old- thats 4500000000 years. Very old…
- Ruth Mitchell answered on 20 Jun 2013:
  
  We don’t actually know! There is some debate about this. 4.5 billion years old comes from evidence from radiometric age dating of meteorite material. But this amuses that the rates of change of processes in the past were the same as we observe today.
  Some people think that the earth is alot younger – around 6 thousand years old. This is based on genealogies from the Bible but also evident form science that contradict that the world is 4.5 billion years old such as the fact that DNA decays too fast (DNA experts insist that DNA cannot exist in natural environments longer than 10,000 years, yet intact strands of DNA appear to have been recovered from fossils allegedly much older) and history is too short (Prehistoric man built megalithic monuments, made beautiful cave paintings, and kept records of lunar phases. Why would he wait two thousand centuries before using the same skills to record history?).
- Ee Lyn Lim answered on 20 Jun 2013:
  
  Hmm…4.5 billion years is sort of an estimated number that most scientists agree on. I don’t know exactly how true that is, but I would think it’s rather older than 6 thousand years! We know that because people in the Mesopotamian civilisation (where Iraq is today) started to leave written records from almost 7 thousand years ago, and we also have historical writings from the Indus (India), Nile (Egypt) and Yellow River (China) civilisations from many thousands of years ago.
  
  For life to evolve from single molecules into intelligent humans who can draw and write will certainly take more than a few years! From what we know about the rate of evolution, it wouldn’t be surprising if it took many millions of years. We have layers of fossils in the ground, and geologists can read the layers of rock and dirt in the ground like tree rings, and that’s how long they think it took. And we don’t know how long it was between the formation of the earth and the first appearance of life. So it’s quite hard to tell really, but Earth is definitely really old!
- Peter Balfe answered on 21 Jun 2013:
  
  In the 19th century, before the discovery of radioactivity, Lord Kelvin calculated from the known temperature of the insides of volcanoes that the earth had been cooling from lava for ~20 – 40 million years. In fact inside the earth heat is being generated all the time by radioactive decay, pushing back that date to where it is now.
- Katy Brown answered on 24 Jun 2013:
  
  I would also lean towards the 4.5 billion years estimate, rather than 6000 years! Most scientists believe that animals and plants evolved very very slowly, and by looking at our DNA now we can estimate how fast it changes. Then, by comparing the DNA of different animals we can estimate how long they’ve been separated from each other. The first organisms with more than one cell are estimated to be 1200 million years old and very early ancestor of humans were around 6.5 million years ago.

Question: how old is earth?

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