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I've seen in several places that there seems to be an extinction cycle on earth of approximately 27 million years. I've read this here:

http://www.dailymail.co.uk/sciencetech/article-1294372/Life-Earth-wiped-27-million-years.html

And also saw a similar explanation on Cosmos last week. Since the Earth is about 4.54 billion years old, that means there have been around 168 different extinction cycles. From what I understand, the Earth will either heat or freeze at extreme temperatures and then either cool or warm until water and life is a possibility again.

Given that this is correct (and definitely correct if I'm wrong, I'm eager to learn!), what are the chances there was a full civilization like ours that got completely wiped out in a different extinction cycle than ours? Is it possible or are there other factors in the history of our planet that would have prevented life from flourished to the point that we are in now?

MxmastaMills
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    This question appears to be off-topic because it is about either Biology or Earth Science (migratable to the corresponding SE site). Overall, a good question, albeit off-topic on SEx.SE. – Deer Hunter May 29 '14 at 07:51
  • Thanks @DeerHunter, I'm new to these forums (though I've been on the coding/tech ones for a while) so I'm still learning. I'll post in there. Thanks! – MxmastaMills May 30 '14 at 19:57

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It's a mesmerizing thought to consider that there may have been an advanced, perhaps spacefaring civilization of "first people" on Earth many millions of years ago, which was wiped out by some global catastrophe.

But, the reality is not that.

Any advanced civilization would be composed of beings with certain properties we find on Earth only in humans. To build a city you need a society, so you need large brains capable of functioning in a complex social setting. You need the ability to formulate and communicate abstract concepts, so you need language, and again, a big brain. And, you need appendages capable of a strong and precise grasp, capable of manipulating tools and other objects.

There is a clear fossil record which shows the evolutionary history of our planet, laid down in sedimentary rock. The same rock shows the extinction events you referred to. Those "pre-extinction" records show no evidence of any creature exhibiting the sort of properties needed to build a city. And, there are no artifacts or fossilized impressions of artifacts buried deep down amongst the dinosaurs or other ancient creatures.

The fossil record shows that big brains are a relatively recent innovation - much more recent than the last extinction event. So, we humans are the first people.

Perhaps some future catastrophe will wipe out our civilization, only to be reborn a million years further on. If that were to happen, even if no human survives the event, no city remains standing, there will still be evidence of our existence preserved in rock for many millions of years. It may not be obvious to the untrained eye, but to a person (or future-being) who knows what they are looking at, it will be incontrovertible proof that we were once here.

Anthony X
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  • Nice, great answer. Thank you! A follow-up question, would there ever have possibly been an extinction event that ruined the Earth so drastically that it destroyed fossils and rocks (i.e. records of the past)? I've read that the oldest fossil found was 3.5 billion years old but it's not conclusive. Do we have a vast record of fossils and life that is billions of years old? – MxmastaMills May 29 '14 at 05:28
  • @MxmastaMills The fossil record is unbroken all the way back to early and simple life. Any event such as you suggest would have left its own mark in that record. If such a thing had occurred, there would be an open question of what filled the gap which this event so thoroughly erased. There is no evidence of such an event, so no gap and no mystery. A previous "first life" would have to have preceded the entire sequence of evolution we know about, 3.5+ billion years ago - another 3.5By of evolution crammed into maybe 1B of Earth's prior existence. Probably not. – Anthony X Feb 18 '17 at 17:52