Carina Hoorn
Looking down at the Amazon River from above, an observer cannot help noticing that water dominates the landscape even beyond the sinewy main channel. The river, which extends from the Pacific highlands of Peru some 6,500 kilometers to Brazil's Atlantic coast, swells out of its banks and inundates vast swaths of forest during the rainy seasons, and myriad lakes sprawl across its floodplains year-round.
All told, the river nurtures 2.5 million square kilometers of the most diverse rain forest on earth. Until recently, however, researchers had no idea how long this intimate relation between river and forest has actually existed. The inaccessibility of this remote region, now called Amazonia, meant that long-held theories about the early days of the river and surrounding forest were speculative at best.
In the past 15 years new opportunities to study the region's rock and fossil records have finally enabled investigators to piece together a more complete picture of Amazonian history. The findings suggest that the birth of the river was a complicated process lasting millions of years and that the river's development greatly influenced the evolution of native plants and animals. Indeed, many researchers now contend that the incipient river nourished a multitude of interconnected lakes in the continent's midsection before forging a direct connection to the Atlantic Ocean; this dynamic wetland produced ideal conditions for both aquatic and terrestrial creatures to flourish much earlier than previously thought. The new interpretations also explain how creatures that usually live only in the ocean - among them dolphins - now thrive in the inland rivers and lakes of Amazonia.
Telltale Sediments
Understanding how and when the Amazon River came to be is essential for uncovering the details of how it shaped the evolution of life in Amazonia. Before the early 1990s geologists knew only that powerful movements of the earth's crust forged South America's Andes and towering mountain peaks elsewhere (including the Himalayas and the Alps) primarily between about 23 million and five million years ago, an epoch of the earth's history known as the Miocene. Those dramatic events triggered the birth of new rivers and altered the course of existing ones in Europe and Asia, and the experts assumed South America was no exception. But the specific nature and timing of such changes were unknown.
When I began exploring this mystery in 1988, 1 suspected that the best records of the ancient Amazonian environment were the massive deposits of mud, sand and plant debris stored in the trough that the mighty river now follows to the Atlantic. But getting to those sediments - long since solidified into mudstone, sandstone and other rocks - posed considerable challenges. A jungle big enough to straddle nine countries with differing laws does not yield its secrets easily. And the rocks forming the trough, which poke aboveground only rarely, usually do so along nearly inaccessible tributaries and tend to be covered by dense vegetation.
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Along the hundreds of kilometers of waterways my field assistant and I surveyed in Colombia, Peru and Brazil, we encountered only a few dozen sizable outcrops. And often we had to wield a machete to cut away the foliage - once surprising a giant green anaconda and another time exposing the footprints of a jaguar. Even then, we could reach only the uppermost layers of the thick rock formation, which extends almost a kilometer below the surface in some locations.
Once the initial fieldwork was complete, my first conclusion was that the Amazon River did not exist before about 16 million years ago, the start of what geologists call the Middle Miocene. Most of the rocks we found that dated from earlier times consisted of the reddish clays and white quartz sand that clearly had formed from the erosion of granites and other light-colored rocks in the continent's interior. This composition implied that the region's earlier waterways originated in the heart of Amazonia. I inferred - and other researchers later confirmed - that during the Early Miocene, rivers flowed northwest from low hills in the continental interior, and some eventually emptied into the Caribbean Sea.
The Amazonian landscape altered significantly soon thereafter when a violent episode of tectonic activity began pushing up the northeaster Andes. By about 16 million years ago in the rock record, the red and white sediments disappear. In their place we found intriguing alternations of turquoise-blue, gray and green clays, brown sandstone and fossilized plant matter called lignite. It was obvious that the dark particles of mud and sand were from a source other than light-colored granites. And distinctive layered patterns in the fossilized sediments indicated that the water that deposited them was no longer flowing north; instead it flowed eastward. My guess was that the rising mountains to the west shifted the drainage pattern, sending water east toward the Atlantic.
In support of this idea, later analysis of the sediment at Wageningen University in the Netherlands proved that many of the brown sand grains were indeed fragments of the dark-colored schists and other rocks that began washing away as the newborn Andes rose up. What is more, some of the pollen grains and spores I found in the clays and lignites came from conifers and tree ferns that could have grown only at the high altitudes of a mountain range. This pollen contrasted with that in the older Miocene sediments, which came from plants known to grow only in the low-lying continental interior. Drill cores of Miocene rocks in Brazil, which provided the only complete sequence of the change from reddish clays to the blue and brown sediments, further corroborated my conclusions.
Finally, scientists had undeniable evidence for when the budding Amazon River was born. But it soon became clear that the river did not establish its full grandeur until much later. In 1997 David M. Dobson, now
at Guilford College in Greensboro, N.C., and his colleagues discovered that the Andean sand grains I found in Amazonia first began accumulating along the Brazilian coast only about 10 million years ago.
That timing means the river took at least six million years to develop into the fully connected, transcontinental drainage system of today. Research into the geologic changes that occurred in that transition period has now illuminated the origins of the region's enigmatic, present-day fauna.
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Book Presentation
(Useful Language)
| (The) Present | ||||
 article
book
essay
paper
| is about is concerned with deals with is devoted to |
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| The book embraces a wide range of problems. | . | |||
| The main emphasis in this book will be on | ||||
| My discussion will be centered on (the following issues) | ( ) | |||
| The paper presents (a comparative analysis of ). | ( ). | |||
| The problem is | , | |||
| The problem raised (studied, considered, discussed) here is | , (, , ) | |||
| The present book is aimed at The present book aims at | ||||
| It is the purpose of this book (survey) to explain the principles of this viewpoint | ||||
| There is a vast literature on | ||||
| On this question there is an enormous literature. | . | |||
| This question has been widely discussed in the literature. | . | |||
| The question of was repeatedly raised in the literature. | . | |||
| In recent years a considerable amount of (valuable) work has been done in | () | |||
| Almost all observers emphasize that | ||||
| Some authors define it as , other view it as | , | |||
| Scholars give us more definite information on | ||||
| The paper abounds in illustrative material, examples. | , . | |||
| It has been established by recent studies that | , | |||
| A great advance in is indicated by | ||||
| Recent works have a direct bearing on the matter under discussion. | . | |||
| It is necessary to give a short review of | ||||
| It is now argued that | , | |||
| It has been argued that | (), | |||
| We may argue that | (), | |||
| There is another proof that | ||||
| It is true that | , | |||
| A careful examination of proves that | , | |||
| It is clear (evident, obvious) that | , | |||
| For confirmation of we will turn to | ||||
| In the light of these data, the discovery of confirms the | , | |||
| This is proved by the fact | ||||
| We have no clear proof of | ||||
| It must be admitted that | , | |||
| There is some evidence to suggest that | , | |||
| It seems essential to emphasize that | , | |||
| It should be noted that | ||||
| A very important point to be made is | ||||
| It should be added that | , | |||
| As we have said | ||||
| As has been mentioned earlier | ||||
| It is generally accepted that | , | |||
| It has often been claimed at present | ||||
| It is known that | , | |||
| It is a well-known fact that | , | |||
| It is commonly known that | , | |||
| It is usually regarded as | ||||
| It is common place to say that | , | |||
| It has become customary to think that | , | |||
| According to this view | ||||
| On the basis of the view it is possible to | , | |||
| Some hold that while others hold that | , . | |||
| The view that is characterized by is | , | |||
| This point of view was stressed by | ||||
| The view that has been widely held in recent years is | , , | |||
| The opposite view was taken by | ||||
| From this point of view it must be regarded as | ||||
| A new theory of was elaborated (formulated, worked out, created) by | () | |||
| There is a theory based on | , | |||
| This is a scientifically valid theory | - | |||
| In the light of the theory it is possible | ||||
| This supports the concept of | ||||
| This conception is current. | . | |||
| The essence of the conception of was expressed in | ||||
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Text Presentation
(Useful Language)
The heading of the text is and it is devoted to the problem of (topic of)
The heading of the text is and it deals with
I ll brief you on the topic and show how the author considers this problem.
talks
considers
speaks
The author firstly / analyses
secondly / then / next / focuses on
finally stresses
outlines
highlights
explains
informs
emphasizes
briefs on
Id like to start with
Now Id like to move to
Id like to say a few words about
In conclusion Id like to
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Topic Presentation
(Useful Language)
The topic of my talk is
The subject can be looked at under the following headings:
We can break this area down into the following fields:
Firstly / first of all
Secondly / then / next
Thirdly / and then we come to
Finally / lastly / last of all
Lets start with
consider
focus on
outline
stress
Ill emphasize
(well) highlight
brief you on
talk about
inform you about
describe
mention
analyse
explain our position on
Lets move / go on to
Now we come to
That covers
In fact
Actually
To sum up
In brief
In short
In conclusion
That brings me to the end of my presentation
Before l stop / finish, let me just say
That covers all wanted to say
Thank you for your attention
Thank you for listening
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English for Presentations
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The Golden Rules of Presentations
Leave nothing to change
Check everything before you are due to speak room, seating, visibility, acoustics and equipment.
Know exactly how to start
Plan the first minute of your presentation down to the last detail. Try to memorize your opening words. This will help you to sound confident and in control.
Get straight to the point
Dont waste time on long boring introductions. Try to make at least one powerful statement in the first two minutes.
Talk to your audience
Many of the best presentations sound more like conversations. So, keep referring back to your audience, ask them questions, and respond to their reactions.
Know what works
Certain things are always popular with an audience: personal experiences, stories with a message, dramatic comparisons, amazing facts they didnt know. Use them to the full.
Be concise
Keep your sentences short and simple. Use deliberate pauses to punctuate your speech.
Speak naturally
Dont be afraid to hesitate when you speak, but make sure you pause in the right places. Remember, you are not an actor trying to remember lines. A certain amount of hesitation is actually quite natural.
Know your audience
Speak for your audience, not yourself. Take every opportunity to show how much common ground you share with them. Address their goals, their needs, their concerns.
