NARRATOR:Listen to part of a lecture in a geology class.
MALE PROFESSOR:As geologists, we examine layers of sediment on the Earth’s surface to [verb] approximate the dates of past geologic time periods.Uh, sediment, as you know, is material like sand, gravel … fossil fragments … that is transported by natural processes, like wind, water flow, or the movement of glaciers.So, uh, sediment is transported, and then deposited, and it forms layers on the Earth’s surface over time.We examine these layers to learn about different geologic time periods, including when they began and ended.
Uh, for example,from about 1.8 million years ago to around 11,000 years ago was the Pleistocene epoch.
The Pleistocene epoch was an ice age.Uh, during this epoch, sediment was made by the kind of erosion and weathering that happens when the climate is colder.And part of those sediments are fossils of plants and animals that lived at that time.
The Holocene epoch followed the Pleistocene epoch when the Earth’s climate warmed up around 11,000 years ago.
The Holocene epoch is characterized by different sediments … ones that form when the climate is warmer.Because the climate changed, the types of plants and animals changed also.Holocene sediments contain remnants of more recent plants and animals. So it’s pretty easy to differentiate, geologically, between these two epochs.
Now there’s growing evidence that the presence of humans has altered the Earth so much that a new epoch of geologic history has begun … the Anthropocene epoch, a new, human-influenced epoch.
This idea, that we’ve entered a new, Anthropocene epoch, was first proposed in 2002.The idea is that around the year eighteen hundred C.E., the human population became large enough, around a billion people, that its activities started altering the environment.This was also the time of the Industrial Revolution, which brought a tremendous increase in the use of fossil fuels, such as coal.The exploitation of fossil fuels has brought planetwide developments— industrialization, construction,uh, mass transport.And these developments have caused major changes, like additional erosion of the Earth’s surface and deforestation.Also, things like the damming of rivers has caused increased sediment production. Not to mention uh, the addition of more carbon dioxide and methane in the atmosphere.Naturally, all these changes show up in recent sediments. And these sediments are quite different from pre-year eighteen hundred sediment layers.
Interestingly, there’s some speculation that humans started having a major impact on Earth much earlier, about 8,000 years ago. That’s when agriculture was becoming widespread.Early farmers started clearing forests, and livestock produced a lot of extra methane.But I want to stress that this is just a hypothesis.The idea that early humans could’ve had such a major effect, well … I’m just not sure we can compare it with the Industrial Age.
Geologists in the far future will be able to examine the sediment being laid down today.Whereas right now we can say that yes, human impact on the Earth is clear, it’ll be future researchers who’ll have a better perspective and will be able to really draw a line between the Holocene and the Anthropocene epochs.
比如，从大约 180 万年前到 11,000 年前左右是更新世时期。
我们进入人类世的这种说法第一次是在 2002 年提出。这种说法是说在大约 1800 年，人类人口已经足够多，达到 10 亿左右，人类的活动已经开始改变了环境。这也是工业革命时期，人类使用煤等化石燃料大幅度上升。对化石燃料的开发给地球带来了广泛的发展，工业、建筑，还有大宗运输。而这些发展引发了巨大的变化，如地球表面额外的腐蚀以及森林采伐。同样，像给河筑坝，也会导致沉积物的增加，更不要说大气层中更多的二氧化碳和甲烷了。很自然的这些变化就会在近期的沉淀物中展现出来。这些沉淀物与 1800 年前的沉积层有很大不同。
有趣的是，还有一种猜测是人类早在 8000 年前就对地球产生了巨大的影响，也就是农业开始广泛开展的时期。早期的农民开始清除森林，并且家畜生产出大量额外的甲烷。但是我想强调一下这只是一个猜想。这种早期人类造成的巨大影响的说法，我只是不确定能否将它与工业时期来相比。