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All current scientific evidence suggests that Earth has existed for approximately 4-5 billion years.

Question's such as these will have different answers, simply because no one knows.

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10y ago
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12y ago

As a single planet the earth is estimated in age by using several sources. First there are obviously still some parts of the surface of the earth that give us a date going back to about 3.4 billion years. However this is only as old as the oldest rock we have found on earth. Such a procedure cannot tell us if there is older rock available or even if there is not it only tells us the earth is 'at least' that age. It doesn't tell us if its older...only that it can't be any younger.

To further evaluate the problem we need to look at how planets form to begin with.

Planets are formed after a sun starts to shine. The debris left around the new star forms rings (much like you might see on Saturn). These rings are known as planetary or solar accretions discs.

The rings slowly begin under the forces of gravity to form larger pieces... as these pieces orbit the new sun the collide and clump together more. Since some travel faster than others the larger pieces accumulate the smaller ones... Over time all the debris in each of these separate accretions rings will eventually be clumped into one or perhaps several planets.

In the case of the Earth we now think there is supporting evidence that there were in fact two separate planets... the early earth or (proto-earth) and another planet about the size of Mars which has been posthumously named Xia.

At some point after both planets formed they collided with one another. So I suppose the real question is when did this happen and how do we know? because this is the start of our planet the previous two planets were not our planet.

Well we know because not every single piece of dust or rock in the original ring of debris is used up. There is still some out there. Every year as the earth orbits the sun it picks up more and more of it. But it will probably never pick up all of the remaining debris. There are probably still a few large pieces too... but although on some videos and in textbooks the earth and the sun are pictured close together and very large. In real terms this is not the case. The distances between the earth and these pieces of debris are actually very large. It is essentially like throwing a tennis ball out of a plane and expecting it to hit an ant on the head. That's easy to do if the entire ground were covered in ants but if there are just a few its very unlikely.

This process of the earth mopping up the remaining bits of debris is called planetary accretion.

Every now and then a piece of debris which matches the same signatures as the rocks we know formed the early earth is just large enough to make it through the atmosphere and when we find these we can date them.

To measure dust sized particles we fly into the upper atmosphere and pick them up with sensors and some really high tech equipment, and Both NASA and ESA have also measured such particles using spacecraft.

So far the results have always been the same. The earth is approximately 4,540,000,000 years old give or take 40 million years. Now when we say 'give or take' 30 million years that might sound a long time but when you consider the total age it actually represents a little under 1% or so.

The reason its such a small time in relation to the overall estimate is that we simply haven't found any rocks in our accretion disc any younger than 4.5 billion years old. That does not mean there aren't a few still there... but its not looking like there are many, and since there are older ones then that's clearly the best benchmark.

The reason there is about a one percent deviation is that all dates are generally supplied in scientific terms with what is referred to as a 'deviation' its basically a mathematical expression of how reliable the actual figure is. So in this case its 99.3% accurate with 99% confidence.

There is not all the debris formed at the same time and indeed some of the debris is not from the original material left at the formation of the sun but was also added as new material after the impact of Earth with Xia. and some material was attracted into the disc of debris from elsewhere in the solar system. However this is less likely than it might sound and accounts for an extremely small percentage of the original material. Far less than the 1% deviation.

Now this of course relies on just the debris in our accretion disc. But to confirm the findings it is likely that other planets formed around the same time. To achieve a better understanding we also need to date the debris in the mars accretions disc and the Venus accretion disc and perhaps even take samples of asteroids etc.

So far as we can in fact measure these by using several forms of spectral analysis of debris etc. they confirm our findings.

So the answer is, as we know it now, the earth is at least 4.54 billion years old.

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11y ago

most people believe that the world has been here for 3 million years.

scientists and me approximately guess about 4,5 billion years

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14y ago

4.5 to 5 billion years

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