at a time?

[bosunyum]

The following sentences are about the Amazone and i have a few questions.

1. The capital of the sate was forced to close its airport for days at a time. what is the meaning of at a time in this sentence?

2.save the rain forest, long a rallying cry for conservationists,is..... Is the underline part grammatically acceptable? As far as I know, it should be a long rallying cry... what do you think?

3.Time and again , the forest has defied predictions that it was doomed. what does this sentence mean? coule you be specific?

4, chemists scour the flora and fauna for compounds with seemingly magical properties. -what does the underlined part mean?

5. The lessons encoded in the genes of the Amazon's plants may hold the key to solving a wide range of human problems.--what is the underliend part mean? especially, what does it mean by lesson?

6.... It wil bring on wrenching climate changes. what does it mean by wrenching ?

7. If the rain forest disappears, the process will begin at its edges.
. what does it mean at its edges?

[Tdol]

at a time = for periods each lasting days
it's correct- it means that it has been a rallying cry for a long time
time and again = repeatedly, so people have said it would fail, but they have been proved wrong over and over
properties that do wonderful things
the lessons are the medical properties, I think
dramatic- likely to ffect our lifestyles, maybe forcing us to move
the forest will disappear from the outside inwards

[bosunyum]

I always appreciate your kind explanation about my questions.
Here , i still don' understand what at a time means in spite of your explation. could you be more specfic?

[Tdol]

It has closed a number of times. Each time it has closed, it has done so for a period of a few days. The phrase emphasise the repeated and lengthy closures (for an airport).