It’s often claimed that we are in the middle of a great mass extinction, caused by human recklessness towards the environment. And certainly, extinction rates are nothing short of alarming, and action urgently needs to be taken – however, in the interest of factual accuracy, if extinction were to stop right now (i.e. if extinction rates went back to ‘normal’, which is probably not all that well defined a notion), would some hypothetical future archaeologist, going by fossil evidence, consider our period one of mass extinction?
The reason I’m asking is that while we’re probably killing off things faster than almost anything else, we haven’t done so for very long, compared to other extinction events. So, how much have we reduced total biodiversity (as measurable through fossil evidence)? In an analysis of the fossil record, would this appear statistically significant to a future archaeologist?
The last 300 years? No.
The last 30,000 years (since about the time anatomically modern humans first appeared)? Sure. Lots of megafauna extinct since then. And that is pretty much a geological eyeblink, although an archeologically long time.
For one thing, the part of the fossil record we have by far the best picture of is marine invertebrates (although even this is hardly perfect). In some regards, this really is the fossil record: we have some limited insight into other types of organisms, but not enough to really establish a good picture of Earth history on their own. So, with that in mind, I don’t believe the human-driven extinction event (prehistoric or modern) has really had much of an effect on marine invertebrates and so I’m somewhat doubtful that it would be recognized as an extinction event of any significance in the fossil record. Maybe if some of the dire predictions about the effects of climate change on the oceans come to pass this might change.
According to The Earth After Us, yes we have already made a visible dent.
The (excellent) book takes the premise that humans themselves become extinct in the near future, and archeologists 100 million years from now are exploring earth. Actually, much of the book is really an introduction to geology and fossil exploration, and the amazing amount of information we can tease out of strata in the earth.
Assuming humans just continue on as normal, and ignoring any global warm effects (which, if true, will cause many changes visible 100 million years from now), there are still fossil records that will be noticeable. DrFidelius mentioned the megafauna loss, but something even more noticeable is plant life. It’s possible to determine with surprising precision the plant life in various regions, just from the fossilized record of pollen it gives off. The book points out the massive reduction in plant variety from large-scale farming of just a few strains of plants around the globe.
That’s not to say we’ve made a lot of plants go extinct - just that the overall biodiversity is way down from a statistical point of view.
You’d be in the minority on that one. While not many specific marine invertebrates are noted as having gone extinct, that doesn’t say much given the paucity of data and the state of taxonomy in the field. But certainly many marine invertebrates are listed as endangered or threatened by monitoring bodies.
Some of this is already happening - coral reef destruction, for instance, is way, way up already, not just because of climate change but also other human actions. And coral reefs definitely show up strongly in the fossil record.
Becoming a fossil is very hard. Not only do you have to die in the right place at the right time, you also have to be not eaten by anything after you die, including microorganisms. You also can not be in the path of any volcanoes, earthquakes or even less likely meteors. Then someone, intelligent enough to recognize a fossil (creationists need not apply), needs to find you before you are eroded away.
Since fossil hunting began we have only found a very small percentage of all the species that have ever existed. It is estimated that well over 90% of all the animals that have ever lived on this planet have gone extinct.
Although we have changed this planet in ways that no other organisms has done in this short a time span, it is still not enough to make any noticeable difference for future scientists.
You are right, we will leave evidence of our civilization, but what I meant was that if a future scientist were to be studying the fossil record before humans, during our civilization and after today there would not be a significant decrease in species. At least not a difference that a future scientist could conclusively blame on us.
Really? Humans have converted huge swaths of the planet from one ecosystem to another for our own use. We’ve cut down forests, tilled grasslands, filled swamps, irrigated deserts to create more farmland. Some of those changes will be permanent, and leave an obvious mark on the fossil record. Others might be temporary, as when a forest is cleared but regrows a few hundred years later. But even that will leave a record in many places; at the very least there will be a thin layer of agricultural deposits between two layers of the usual forest soils.
For marine fossils (well limnological to be precise), consider shellfish in the Great Lakes. Just a few decades ago the zebra mussel invaded and replaced just about every other type of shellfish throughout the lakes. The zebra mussel has also altered the ecosystem rather dramatically, altering populations of other species like fish. There will be a fossil record with a dramatic and obvious change from many species of mussel to large populations of another.
That is an excellent point, and I do not dispute that a future scientist will be able to tell that we changed many parts of the earth. But any changes will be very minute and be almost gone in a few thousand years if humans were to disappear today. Of course stainless steel and plastic will be around for a much longer time than that but that is hardly anything that will impede life on this planet.
The original question was whether there would be any apparent change in the number of species in the fossil record due to human activity. I stand by my no.
Yes, and, then again, no. Some organisms are guaranteed, by their makeup and location, to fossilize in greater probability than, say, vertebrates - forams, coccoliths, that sort of thing.
Part of the problem is HOW long humans dominate/control the changed ecosystem and how long does it take for it revert back to normal (if it can) in the area where fossils are being created?
Lets say humans move into an area and decimate the local alligator population. This goes on for a hundred years then humans just disappear for whatever reason. The alligator population rebounds. Millions of years go by. Someone starts digging up fossils in that area.
IMO that hundred year blip will not be detectable in the FOSSIL record. Its going to have a be significantly longer than that. In your typical fossil record, whats the number of years per inches of strata thickness?
The bulk of the book I reference argues the exact opposite - the reduction in species in the fossil evidence will be very noticeable, according to it. It concentrates more on plant (including microscopic pollen) and marine fossils (including coral, as mentioned by MrDibble, and makes the (convincing to me) case that it’s already been enough effect to be very noticeable to future scientists who are at least as skilled as we are.
It also talks about the direct evidence left by humans, and from it the author concludes that future scientists (in this hypothetical case, aliens researching earth, with no prior knowledge of humans) will determine the changes were caused by an intelligent species, not some planet-wide natural process.
And these conclusions were from the premise of looking into the fossil record 100 million years from now, when large parts of today’s surface earth will be gone (underwater, shifted under ground, etc.)
We have already seen a great decrease in the megafauna that was present during in the Pleistocene, almost certainly in large part due to human impacts. This is glaringly obvious in the fossil record. And subfossil remains demonstrate that probably thousands of species of birds were lost in the islands of the Pacific during human colonization of the region.
I completely agree with your statement but I think my error was the assumption that the original question was referring to a mass extinction, comparable to the mass extinction after the KT boundary.
The direct answer to the OP is that no, we are not yet in a mass extinction event comparable to any of the “Big Five,” in which 50% of all genera died.
This is what I am contesting. There have been significant decreases in the number of species due to human impacts, especially among large terrestrial species and species on islands, that are detectable (and have been detected) in the fossil record.
These are not, however, anywhere near the level of the greatest mass extinctions in geological history. It remains to be seen, however, what the ultimate result of current anthropogenic change will be.
Thanks for the excellent answers. There’s a number of things that I didn’t consider at all that have been highlighted – the extinction of megafauna (I didn’t even consider that our influence on the environment reaches back further than the couple of hundred years we’ve been in the game on the big scale), reduction in plant species diversity, coral reef destruction etc. The Earth After Us is definitely going on the ‘to read’ list.
One follow up question about the rate at which species are going extinct: by this criterion, are we experiencing a ‘Big 5’ level mass extinction event? I.e. if current trends continue for as long as those events have lasted, will the reduction in number of genera be of a comparable order of magnitude? I’m guessing the answer to that will be yes, but I’m looking for some facts to substantiate that guess.
We have shuffled the fossil record a bit with all our digging. Suppose Jack Horner gets fossilized next to some of his dinosaur finds. What would future paleontologists think?
