我最近很好奇地了解到古新世-始新世热极大值从约翰·贝兹的这个博客。对于那些还没见过的人来说，这是一个标记为“PETM"在这张(来自维基百科)过去6500万年全球温度的图表中:

这立即让我震惊，这一事件在某种程度上与现代气候变化相似——维基百科文章中也提到了这一观察结果。显然，推测古新世-始新世热极值可能是由火山爆发引起的。< / p >

(In asking the following question, I am not saying that I believe this to be the case (indeed, I find it highly implausible). I ask simply out of scientific curiosity.)

Is there any way we could tell whether the Paleocene–Eocene thermal maximum was caused by an ancient race of intelligent life forms, who caused a period of global warming in similar fashion to what humans are doing currently, and subsequently went extinct?

The answer I expect is along the lines of "No, we can't exclude that for sure. But we would expect to see some fossil records from such a civilization, which we don't." But I would be happy to be surprised in either direction by someone more knowledgeable. Some food for thought:

• This answer indicates that there is uncertainty about what actually caused the PETM.
• I have heard it said that there are only two things humans have accomplished which will leave a permanent mark on the geological record. The first is climate change. The second is leaded gasoline, which will leave an identifiable stratum around the globe.

tl;dr:

不，我们不能肯定排除它。但我们希望看到一些来自这样一个文明的化石记录，但我们没有。

是的，差不多就是这个。< / p >

To elaborate, I would refer to your statement that:

I have heard it said that there are only two things humans have accomplished which will leave a permanent mark on the geological record. The first is climate change. The second is leaded gasoline, which will leave an identifiable stratum around the globe.

This is absolutely incorrect. There are so many signatures that our civilisation is leaving at the moment in the geological record, permanently. Some examples:

1. Mining activities. Assuming your civilisation is extracting resources from the Earth to power their fossil fuel industry, then need to mine the stuff. We are talking about huge holes in the ground. There are no currently known cases of an ore deposit that looks like someone has mined out the valuable stuff millions of years ago, leaving behind a hole (whether currently filled or not) surrounded by lower grade material. What about tailings ponds? Large areas of shallow water (with sediments forming at the bottom), full of stuff that isn't usually found together. This would be very easy to find.
2. Electricity. High voltage power lines. You just don't have very long and thin lines of copper or aluminium forming in nature. Even if they don't remain in their metallic form, copper oxide or carbonate, and aluminium oxide or hydroxide don't form horizontal veins that cut across pretty much everything.
3. Agriculture. The huge amount of fertiliser dumped onto farms, and then washed away in rivers forms very large anomalies of nitrogen and phosphate. Again, something that would stick out like a sore thumb in the geological record.
4. Rare earth elements (lanthanides) and gadolinium. These elements form very distinct concentration distributions in natural rocks and sediments. Humans are using individual elements out of the entire lanthanide group, and this ends up in rivers and then in the ocean. Once the concentration anomalies are out there, they are not going anywhere. We have very sensitive ways to detect even tiny differences of these elements from what they should be in natural systems.
5. Landfills. A whole soup of elements that should not be together. No natural system can form this. They're buried in the ground, and they stay there.
6. Megacities. Tokyo, New York, London, Sydney. Huge amounts of asphalt, concrete, glass, steel, aluminium. Overground and underground. Even if you collapse and erode whatever remains, you will have huge areas covered with former cities, forming rock formation that are otherwise not possible in natural geological processes.
7. Nuclear waste. I reckon there's no need to add anything here - right? Obvious that these things will not form in nature.

The list goes on and on. Trust me, if there was a civilisation large enough and advanced enough to destroy itself, we would see that very well in the geological record.

Now we have maps of the lunar surface with a resolution of about 100 metres. This would by far not be enough to find the Apollo landers by chance, but our current civilisation is not far away from leaving larger structures on the moon, so it seems to me there is a big probability that previous industrial civilisations would've left something that sticks out like a sore thumb on the lunar maps that we already have.

There are plans to build the Lunar Gateway Station, a space station in orbit around the moon, by the end of this decade. While that's still not large enough to be found on current maps, you can easily expect a larger station only a few decades away. A station the size of the ISS from 55 million years ago would either still be orbiting the moon or (ore likely) have crashed into it by now, but in either case we should've found the debris. We will probably also build structures on the moon itself in just a few decades, whether research stations on the scale of the Antarctic stations or perhaps some exploratory mining for trace metals (whether that's ever economically viable is a different matter).

The point is that Earth's surface has changed so much that likely only very large structures (like megacities) can still be found, but may be deformed so much that we don't recognise them, while on the Moon even comparatively small structures of just a few hundred metres (or much less in some places) would still be very obvious.

一个物种能在不开采碳氢化合物的情况下显著改变气候吗?或者他们能在不留下痕迹的大技术足迹(道路、电网、核电等)的情况下，以所需的规模开采碳氢化合物吗?< /强> < / p > < p >我会认为你会寻找类似的一种食肉文明,不需要援助,亨特(没有武器像燧石需要增加税后热量从狩猎),几乎没有兴趣猎物增加农业/喂它们(没有化肥/农业增加饲料的猎物,没有脂肪的牛群驱赶其他野生动物),和不需要住房/商品添加保护/舒适——需要re-distributed资源。当然，一旦你假设一个这样的文明——他们需要这种力量做什么?交配展示/文化原因只能消耗这么多汽油。而且，他们必须看到不良影响正在发生，并且有理由不遏制他们的过度行为。