Chapter 2 - Written in the Rocks Flashcards
1
Q
Charles Darwin (quote)
A
The crust of the earth is a vast museum; but the natural col- lections have been made only at intervals of time immensely remote.
2
Q
Tangible historical evidence for evolution
A
- Paleontologists have worked tirelessly to piece together the tangible his- torical evidence for evolution:
the Fossil Record. - To biologists, fossils are as valuable as gold dust
- Fossils have been known since ancient times:
Aristotle discussed them, and fossils of the beaked dinosaur - Even in the nineteenth century, they were simply explained away as products of supernatural forces, organisms buried in Noah’s flood, or remains of still living species inhabiting remote and uncharted parts of the globe.
3
Q
Formation of fossils
A
- First, the remains of an animal or plant must find their way into water, sink to the bottom, and get quickly covered by sediment so that they don’t decay or get scattered by scavengers. (This is why most of the fossils we have are of marine organisms)
- Once buried safely in the sediments, the hard parts of fossils become infiltrated or replaced by dissolved minerals.
What remains is a cast of a living creature that becomes compressed into rock by the pressure of sediments piling up on top.
Because soft parts of plants and animals aren’t easily fossilized, this immediately creates a severe bias in what we can know about ancient species.
- Once a fossil is formed, it has to survive the endless shifting, fold- ing, heating, and crushing of the Earth’s crust, processes that completely obliterate most fossils.
- Taking into account all of these requirements, it’s clear that the fos- sil record must be incomplete
- Ironically, the fossil record was originally put in order not by evolu- tionists but by geologists who were also creationist
4
Q
Radioactivity
A
Since about 1945 we have been able to measure the actual ages of some rocks—using radioactivity.
5
Q
Dating
A
- One method uses biology, and involved an ingenious study of fossil corals by John Wells of Cornell University.
- Corals: He made use of the fact that the friction produced by tides gradually slows the Earth’s rotation over time.
Each day—one revolution of the Earth— is a tiny bit longer than the last one.
Not that you would notice: to be precise, the length of a day increases by about two seconds every 100,000 years. Since the duration of a year—the time it takes the Earth to circle the Sun—doesn’t change over time, this means that the num- ber of days per year must be decreasing over time
6
Q
Eukaryotes
A
Organisms having true cells with nuclei and chromosomes.
7
Q
Tetrapods
A
Four-legged animals, the earliest of which were lobe-finned fish.
8
Q
Humans
A
- Humans are newcomers on the scene.
- Our lineage branches off from that of other primates only about seven million years ago.
- If the entire course of evolution were com- pressed into a single year, the earliest bacteria would appear at the end of March, but we wouldn’t see the first human ancestors until 6 a.m. on December 31. The golden age of Greece, about 500 BC, would occur just thirty seconds before midnight..
9
Q
Missing Links
A
- Changes in marine species may give evidence for evolution, but that’s not the only lesson that the fossil record has to teach.
- What really excites people—biologists and paleontologists among them—are transitional forms: those fossils that span the gap between two very different kinds of living organisms.
- According to evolutionary theory, for every two species, however different, there was once a single species that was the ancestor of both.
- We could call this one species the “missing link.”
- As we’ve seen, the chance of finding that single ancestral species in the fossil record is almost zero.
- The fossil record is simply too spotty to expect that.
- But we needn’t give up, for we can find some other species in the fossil record, close cousins to the actual “missing link,
10
Q
Transitional species
A
- Not equivalent to “an ancestral species”; it is simply a species showing a mixture of traits from organisms that lived both before and after it.
11
Q
Fish to Amphibians
A
- One of the greatest fulfilled predictions of evolutionary biology is the discovery, in 2004, of a transitional form between fish and amphibians.
- This is the fossil species Tiktaalik roseae, which tells us a lot about how vertebrates came to live on the land.
12
Q
Vertebrates: Fish
A
- Until about 390 million years ago, the only vertebrates were fish.
- But, thirty million years later, we find creatures that are clearly tetrapods: four-footed vertebrates that walked on land.
- If there were advantages to venturing onto land, natural selection could mold those explorers from fish into amphibians.
- That first small step ashore proved a great leap for vertebrate-kind, ultimately leading to the evolution of every land-dwelling creature with a backbone.
13
Q
Tiktaalik roseae
A
- Tiktaalik shows that our ancestors were flat-headed predatory fish who lurked in the shallow waters of streams.
- It is a fossil that marvelously connects fish with amphibians.
- And equally marvelous is that its discovery was not only anticipated, but predicted to occur in rocks of a certain age and in a certain place.
14
Q
Origin of Birds
A
- Since the nineteenth century, the similarity between the skeletons of birds and some dinosaurs led paleontologists to theorize that they had a common ancestor—in particular, the theropods: agile, carnivorous dinosaurs that walked on two legs.
- Around 200 million years ago, the fossil record shows plenty of theropods but nothing that looks even vaguely bird-like.
- By seventy million years ago, we see fossils of birds that look fairly modern.
- If evolution is true, then we should expect to see the reptile-bird transition in rocks between seventy and 200 million years old.
15
Q
Mosaic
A
Rather than having every feature being halfway between those of birds and reptiles, Archaeopteryx has a few bits that are very bird-like, while most bits are very reptilian.
