SPEAKER: Let's talk a little bit about stratigraphy, the formation of strata. Stratigraphy refers to levels. And in many circumstances in geology, we find that the older levels first deposited are going to be at the bottom of a stratigraphic profile while those at the top are most recent. So when Farmer Brown digs a hole in his field, he's standing on firm ground of the present day and digging a hole, but the hole may go down to a deposit of about 10,000 years.
Now, if archaeologists many years in the future look at the material at the bottom of that hole that Farmer Brown may have placed there, he's going to find or she is going to find evidence that is not 10,000 years old but rather something intrusive from the surface. This is just one example of how stratigraphic sections become disturbed. They can be disturbed by geological agencies-- earthquakes, floods, fires, volcanic activities. Once these are disturbed, then, of course, the nice layer cake order that we have in stratification is interrupted.
The importance of these strata for us is that they contain materials of interest, mainly fossils and in the case of later humans cultural artifacts, products of human culture. And as we need to know the date of the stratification, we are able then to determine something about the date of the cultural artifact. But at the same time, artifacts made at a certain period of time may also help the geologists to date the stratification.
We call these stratifications that contain the remains of living things biostratigraphic units. And they are in time contexts that are called chronostratigraphic units. So the relationship of the chronology, the time, and the biology, the fossils, tell us about a sequence that we would not have just by looking at a layer cake disturbed or undisturbed.
One of the reasons that we need to know this is that it allows us to have dates for the material we're examining particularly in cases of fossil human remains. Because without that information, we're in a very poor position to know what the relationships of the fossils may be to one another. Just as we will find fossils of elephants and bears, pigs and cows and horses, mammoths, dinosaurs in stratigraphic contexts, so also we find human remains.
Now, human beings live on top of their debris so that in looking at a cultural sequence, again, unless it's disturbed, we're likely to find the earliest cultural evidence in the lower bottom of the stratification and the more recent material toward the top. It's because of this collection of artifacts, material cultural events and circumstances of invention and technology, in association with the fossil material that we are able to build a profile of how earlier people lived. And with respect to the animals and plants that are found with them, we are able to reconstruct the ancient ecology and environments, the climates, and the other natural events that are taking place at the time of those particular human occupations.
How long ago did we find our first human ancestors? Well, the universe itself is about 15 billion years old. The Earth and the solar system is about 4.5 billion years old, and about a million years ago, we find the first evidences of living things.
These are single-celled animals. And geologically, we put them into a particular era of geological time. It is not until much later in other eras with their subdivisions of periods and epochs that we begin to see the rise of mammals.
And by about 65 million years ago, we have the first examples of animals that we can relate to the order, the taxonomic order, to which we belong. And that order is called the primates. And you all know what primates are because we've all been to the zoo or zoos. And you have seen monkeys and apes.
The monkeys are found either in the new world or the old world. They used to be in Europe. But except for the Isle of Gibraltar, they're not there today. In Southeast Asia, you have the apes, the gibbons, and the orangutans, and in Africa, of course, the large apes-- the chimpanzee and the gorilla.
Now, these apes are not our ancestors, of course. They're our contemporaries. They had their fossil ancestors just as do we. But I'll tell you something very interesting. It's only been about 4.5 million years ago that the living apes and us as living humans had a common ancestor. Some fossils of that common ancestor have been recovered. They date to about 4.5 million years in some deposits in Africa.
We have a very well-established fossil record in later periods of our human history. But at least we can go back now to the period that shows the earliest examples of a common ancestor.
Missing link? No, that's not what we call that. A missing link is a concept that comes out of the Middle Ages, which is very different from what we're talking about in transitional forms and in forms of animals that were able to bifurcate for natural selection and adaptation reasons into different living groups, some of which survive today, namely the great apes and ourselves.
But don't be mistaken. We are also apes. It's only our vanity as human beings that lets us think that we belong to a very special part of that creation. And as we go back in time to these early humans that show so many characteristics with apes in the fossil record, we can verify that. We can also verify it through molecular biology and comparative anatomy and other scientific approaches.
So our understanding of ourselves as members of the primates while going back about 65 million years ago allows us only to find our own immediate ancestors about 4.5 million years ago. And these are found in stratigraphic contents in the biostratigraphy of various sites. And after that period of 4.5 million years ago, we find other fossils that we definitely would relate to members of the human family but not necessarily modern in their appearance and showing many characteristics that are shared with our common ape ancestors.
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Since the time of separation of the evolutionary lines of apes and humans about 5 million years ago, some fossil specimens of the skeletal remains of our earliest ancestors have been preserved and discovered. Putting together the pieces of the puzzle of human biological history is the task of paleontologists, geologists and anthropologists.
In this room we explore how these scientists can reconstruct the past from their studies of the geological contexts in which fossils are found, the dating of the specimens, their comparative anatomy with extinct and living species of our taxonomic order, the Primates, and the lifeways and behavior patterns of the first members of the human family within the Primates.
By looking at reproductions and pictures of this fossil record, including representations of pre-human Primate species, we learn about our prehistoric beginnings among those populations of first two million years of our evolution, as identified as Ardipithecus, Australopithecus and the earliest members assigned to our own genus- Homo habilis and Homo rudolfensis.
This video is part 2 of 13 in the Human Paleontology series.