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IELTS Preparation Series 2, Episode 8: Air Archive


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0:13

Hello. I'm Margot Politis. Welcome to Study English, IELTS preparation.

0:18

Today we're taking a look at tenses. We'll focus on the present perfect and simple past

0:25

tenses, and we'll hear examples of each.

0:29

Then, we'll practice using some adverbs of time.

0:32

The clip we're looking at today is about greenhouse gases. Scientists have been measuring the

0:39

concentration of certain gases, stored in ice in Antarctica. Let's find out more.

0:49

The air archived in ice helps prove how much the level of greenhouse gases in the atmosphere

0:54

has changed in just the last two hundred years.

1:00

What we've found out is that indeed there were much lower concentrations pre-industrially,

1:04

around about a third of the methane concentration that we have presently. We've seen a big increase

1:11

in carbon dioxide, so the two main greenhouse gases in the atmosphere have increased.

1:17

If you look back a half a million years ago, we don't see concentrations anything like

1:24

we have presently. We can link those high concentrations of the present day uniquely

1:26

to activities of man - combusting of fossil fuels, clearing of lands and so on, agricultural

1:34

activities.

1:35

As you know, there is a variety of verb tenses in English - simple, perfect and continuous.

1:45

Tenses are used to describe 'past', 'present' and 'future' actions.

1:51

Sometimes, we need to give more information about when an action happened, how long it

1:56

happened for and whether it is continuing.

2:01

When an action has been completed, we use the present perfect tense.

2:06

Listen to Dr Etheridge use it here.

2:11

What we've found out is that indeed there were much lower concentrations pre-industrially,

2:12

around about a third of the methane concentration that we have presently. We've seen a big increase

2:21

in carbon dioxide, so the two main greenhouse gases in the atmosphere have increased.

2:27

Dr Etheridge uses the present perfect tense.

2:31

He says: 'we've found out'

2:36

He's talking about an action that has been completed.

2:40

He also says: 'we've seen', and

2:44

'greenhouse gases have increased'.

2:48

These actions started sometime in the past but have now been completed - they are in

2:54

the present perfect tense.