spanning the entire northern part of Africa.

Yet it hasn't always been dry, archaeological and geological research

shows that is undergone major climatic changes over thousands of years.

Natural climatic shifts brought the African monsoon rains further north transforming the landscape.

This period between 11,500 and 5,000 years ago is called the African Humid or Green Sahara period.

Rain was far more abundant and vast areas of the Sahara

became savanna grasslands crossed by numerous waterways and lakes.

People have lived in the Sahara for thousands of years relying on these water systems

hunting, gathering, fishing and later herding animals along its fertile corridors.

Rock art is one of the best records of the life of past peoples who lived across the Sahara

It often depicts extraordinary images of life, landscape and animals

that show a time when the Sahara was much greener and wetter than it is now.

Some of the oldest rock art found in the Sahara is 8,000 to 12,000 years old

This period is called the Early Hunter period

and it often focuses on naturalistic engravings representing wild animals

Generally large mammals represented are typical of the savanna

or wetland environments that existed during the early Green Sahara.

These engravings have been connected to hunter-gatherer fisher cultures

followed wild game and waterways across the Sahara

The Messak plateau in the central Sahara contains thousands of rock art engravings

including some of the oldest rock art in the Sahara.

Found in this plateau is a large engraving depicting a crocodile walking with its hatchling

life-sized at more than two metres long, it dates back to a time when crocodiles were found in waterways

before the Sahara became drier, around 5,000 years ago.

There are still a few relic populations of crocodiles that can be found even today in isolated Oases.

Here we can see an engraving showing the outlines of a human figure next to a large elephant.

It is a good example of the naturalistic style of the early hunter period

the image probably depicts the savanna elephant which roams the grassy plains and woodlands of the savanna

and is now found largely in southern and eastern Africa.

These two exceptional engravings of giraffes are in northeastern Niger

The area has been part of the trans-Saharan caravan trade for up to two millennia

but archaeological evidence shows much older occupation dating back over 8,000 years

The two giraffes are life-sized measuring 5.4 meters

the engravings cannot be seen from ground level they are only visible by climbing onto the outcrop.

It is easy to imagine past peoples watching these long necked graceful animals

in the former savanna below and immortalizing them in stone for future generations.

Most rock art found today in the Sahara dates from the pastoral period roughly 7,500 to 4,000 years ago.

This type of rock art focuses on domesticated cattle and scenes of daily pastoral life.

Animals began to be domesticated in the Sahara around 7,500 years ago

and represent a major shift in lifestyle of the local people

in a period that was progressively getting drier and less green.

In the Tassili n'Ajjer plateau in Algeria is a site known as the crying cows.

These skillfully engraved images depict long horned cattle

with carved teardrops appearing to roll down their faces

They're thought to date between 7,000 and 8,000 years ago when this environment was wetter.

These engravings are incorporated in a local myth that tells of a shepherd

who engraved them after being unable to find water for his herd.

Climatic data shows a period of aridity around 8,000 years ago

which may coincide with these engravings and with the associated myth.

Camels were present in North Africa from roughly 2,000 years ago when the Sahara was as dry as it is today.

Their ability to survive in harsh climates allowed major trans Saharan trade to flourish

as people, goods and ideas moved across the desert a new type of rock art developed.

Now called the camel period.

In addition to camels subjects include highly stylized human figures, flocks of goats

caravans, palm trees and hunting or battle scenes.

This camel is part of a complex scene located in Chad on the southern edge of the Sahara

probably representing a camp with animal herds.

Camels feature widely in rock art across the Sahara

their resistance to heat and ability to survive with small amounts of water

have made them key animals for inhabitants of the Sahara

deeply bounds their economy, material culture and lifestyle.

It is not surprising that camels are considered the ships of the desert

transporting people, commodities and goods throughout the Sahara.

Around 7,000 years ago the Sahara began changing to a desert with natural climatic shifts.

As it dried out grasslands and lakes disappeared desertification processes were accelerated

as vegetation which helps generate rain was lost causing even less rain

and the soil lost its ability to hold moisture, the result: desert.

As the Sahara dried out rock art has become one of the best records of life in the past

and the animals and humans that inhabited it for thousands of years.

Although its original purpose and meanings have long since been lost the expressive power

of the engravings and paintings still remains allowing us to gain a small view into the world of the people

that lived in the Sahara thousands of years ago when it was a sprawling green savanna.

Sadly now the extremes of man-made climate change is causing rock art to be endangered and destroyed

forever losing thousands of years of our shared human history.