Listening audioscript

1. HOW DOES THE PROFESSOR ILLUSTRATE THE CONCEPT OF 
PHOTOTROPISM? 
2. ACCORDING TO THE PROFESSOR, WHAT IS THE SIGNIFICANCE OF PEA 
PLANTS? 
3.INDICATE WHICH PARTS OF A PLANT EXHIBIT EACH TYPE OF TROPISM, 
ACCORDING TO THE DISCUSSION. 
 
PASSAGE TWO 
 
Page 194
[ mp3 065-066]
 
Questions 4 through 6.
Listen to part of a lecture in an archaeology class.
(Professor)
Today I want to talk about the process of fossilization. It’s important to 
understand that the distinction of becoming a fossil is bestowed upon 
very few organisms—the conditions have to be just right. And of course, 
this makes sense. Complete decomposition is the normal end of all 
organisms that live. If it weren’t, vital nutrients wouldn’t be recycled into 
the food chain, and there would be fewer and fewer basic nutrients that 
life needs to flourish. 
So, my point is that fossilization is necessarily very rare. And 
furthermore, as we’ll see, the process is very selective. It favors the 

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preservation of some types of animals over others. Let’s take an ocean 
creature, say a fish, and a land creature…um, let’s use some kind of 
small lizard that lives near a river. First of all, the creature dies, and it’s 
best if it’s buried soon after dying. If it’s not buried, then it will probably be 
torn apart by scavengers, looking for an easy meal, or it will certainly 
decompose if left lying out on the land. In the case of our fish and lizard, 
maybe a huge flood buries the lizard near his river home, and then 
washes dirt into the sea, burying our recently deceased fish before it has 
a chance to break down completely.
Now, soft tissues, skin and fat for instance, will eventually 
decompose…um, but if there is not enough oxygen present to completely 
break down the organism, the hard tissues, like bones, shells, and teeth 
may remain. Already you can see that fossilization favors creatures with 
some hard elements to their bodies, creatures with skeletons or shells. 
Soft tissues themselves are generally not preserved, but we can see 
fossils of soft tissues that are actually imprints of soft creatures. What I 
mean is that the body of the soft creature has completely decomposed, 
but the space left might be filled by sediments. You might say that they 
are mineral casts or molds in the shape of the body. 
So, our fish and lizard both have a higher likelihood of being preserved 
than many, many other creatures that do not have mineralized, hard 
body structures. But after being buried under sediment, the next part of 
the process is where the fish has an advantage that the lizard does not. 
OK, so we have our fish and our lizard skeletons both buried under 
sediment. On land, the tendency, even under sediments deposited by a 
big flood, is for all of this to continue to erode. The forces of wind and 
water tend to take away sediments, whereas in the sea, the tendency is 
to build up the sediments that come from the land. So already, just by 
virtue of being a sea creature, our fish has an enormous advantage over 
our land-based lizard in the likelihood of becoming a fossil. 
So, over millions of years, in order to become a fossil, the remains of the 
creatures must stay undisturbed, locked away from the forces of 
decomposition and erosion. But let’s say here that the flood was caused 
by a great geological shift, such as a sudden climate change from a 
volcanic eruption, and that sediments continue to accumulate over both 
the lizard and the fish. 
Now, the next step in the process is mineralization. Although buried deep 
within sediments that have continued to pile up, the buried remains will 
be in contact with minerals around them and in the groundwater. 
Minerals, especially those dissolved in groundwater, can fill up the 
spaces in living tissues, for example in the pores or tiny holes between 
cells of bone. This process is called permineralization—the filling up of 
the spaces in living tissues with minerals. And this process can 
sometimes continue until the hard organic tissue is completely replaced 
by minerals. This is simply called, no surprise here, replacement. So, 
that’s easy to remember, but of course there’s another technical name 
for it: petrification. 
At some point, with many meters of sediment having turned the 
skeletons of our creatures into stone, quite literally, they are now fossils. 
But, buried underneath tons of rock, they remain completely hidden. So, 

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there must be one more process that brings these fossils to light. After 
having sediments deposited on top of it for millions of years, the land 
around our fossilized fish and lizard must then begin to rise out of the sea 
and emerge. The geological processes that are always moving and 
shifting the Earth now lift the land to surface where the forces of erosion 
can wear away all the layers that have built up over time. Only then can 
we find the fossils. So, you can imagine just how many fossils are locked 
away deep in the Earth, never to see the light of day, or how many 
possibly came to the surface before humans were around and then 
eroded away to nothing. 
When someone spots our lizard and fish, now made mostly or completely 
of minerals, and ever so carefully brushes away the surrounding rock to 
reveal them…um, this is only possible because there has been a long 
series of chance events that led to this newfound fossil.
Certainly some creatures are more likely than others to become fossils 
by virtue of the living conditions in their living environment. You can 
understand that range is a factor, too. That is, if a species is spread over 
a wide area, it is more likely that somewhere, the conditions will be just 
right to fossilize an individual of that species. And the physical 
characteristics of the creature make a huge difference in the likelihood of 
its preservation as a fossil. Harder tissues preserve better. But even with 
all of these different factors, I hope you appreciate the sheer 
improbability that any one organism, of any type, will be buried just so 
perfectly, become a fossil, and then surface again for us to find.