This posting is only my English typing practice.

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Because dry deserts are notoriously poor environments for fossilization, 

it has been difficult tot reconstruct the biotic history of deserts.

Is a particular desert old or young? 

Did deserts move closer to the equator during glacio-plu-vial periods,

or did they stay where they were,

but with greatly contracted areas? 

Are the desert communities seen today the same ones that existed before and during the Pleistocene?

Where did desert vegetation survive during the mesic pluvial periods?

Many of these questions remain largely unanswered, 

but they are the focus of much current research.

Traditionally, the history of deserts has been inferred mainly from theoretical paleoclimatological models,

reinforced wherever possible by fossils, especially pollen records from the sediments of pluvial lakes.

Neither provides a very reliable account of the small-scale history of deserts.

In recent decades, a new type of fossil data has been used to reconstruct the vegetational history of one complex region:

the desert zoned of the semiarid and arid southwestern United States ( e.g., Betancourt et al. 1990; Grayson 1993).

Pack rats(Neotoma) are abundant rodents in xeric habitats.

They hoard plant materials in large caches, which are sometimes protected in caves or under rock ledges.

The remains of these caches become solid structures, called middens, 

and persist for thousands of years if kept dry.

They are excellent sources of plant fossils because they provide a relatively complete and often quite continuous sample of the plants growing within 100m of the rats' den during its occupation.

By collection pack rat middens at different elevations and locations and dating the materials using radiocarbon methods, researchers can reconstruct the shifts in elevation and composition of vegetation types and deduce past climatic regimes(i.e., those back to 40,000 years B.P.).

Data from pack rat middens are continuing to e synthesized ( Van Devender 1977; VAn Devender and Spaulding 1979; Wells 1979l Betancourt et al. 1990; see also Fritts 1976),but some general trends are apparent. 

It is clear that there have been major changes in the vegetation at all elevations throughout the arid Southwest within the last 20,000 years. In general, climates in this region were substantially cooler and wetter during the most recent(Wisconsin) glacial maximum.

During this period, vegetation zones were displaced as much as 500 to 1000 m below their present limits(Figure 7.22).

The change to the present configuration of climates and vegetation types occurred primarily within the last 8000 to 12,000 years.

In general, pack rat middens reveal a history consistent with that found in pollen records and geological studies of pluvial lakes, but they provide a much more detailed picture of vegetation changes. 

It is now clear that plant communities did not simply move as entire entitles up and down the mountains.

Rather, they changed dramatically in composition.

For example, during the most recent glacial maximum (21,000 to 15,000 years B.P.),

most plant species in the Grand Canyon occurred 600 to 1000 m lower than at the present time.

This finding indicates a cooler, wetter climate (Cole 1982), Many of the species that inhabited areas along the rim of the Grand Canyon, however, are no longer found in similar communities in the same region today.

In fact, the community contained several species that are presently found in northeastern Nevada and northwestern Utah, at least 500 km to the north (Cole 1982).

Many of the plants now dominant in the coniferous forests of the inter mountain West (e.g., ponderosa pine and pinon pine) were rare and restricted in glacial times. On the other hand, species that were much more widespread 10,000 to 30,000 years ago are now narrowly distrivuted or no longer occur in this region.

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It is very popular drama in Korea and all of the Asia.

It was made by Korea & China.

The main Actor is Song Joong Ki and Jin Goo.

The main Actress is Song Hye Kyo and Kim Ji Won.

Song Joong Ki's name is Yoo Si Jin in drama.

Jin goo is Seo Dae young and Song Hye Kyo is Kang mo yun, Kim Ji Won is Yoon Myung Joo in drama.

Yoo Si Jin & Seo Dae Young & Yoon Myung Joo are army.

But Yoon Myung Joo is a doctor.

Kang Mo yeon is a Doctor.

I attach some video.

I Believe It attract you.

Thank you.