Quiz of the Day
Deserts & Drought
Wednesday, 17 June 2026
World Day to Combat Desertification — desert facts, water science, arid ecosystems
1. What percentage of the Earth's land surface is covered by deserts?
- About 33%
- About 20%
- About 10%
- About 50%
One-third of all land on Earth is desert or semi-arid. That is roughly 50 million square kilometres — an area larger than the entire continent of Asia.
2. Which is the largest desert on Earth?
- Arabian Desert
- Gobi Desert
- Antarctic Desert
- Sahara Desert
Antarctica receives less than 200mm of precipitation per year, making it technically the world's largest desert at 14.2 million square kilometres. The Sahara is the largest hot desert at about 9.2 million.
3. What is 'desertification'?
- Irrigating desert land for farming
- The natural formation of sand dunes
- The process by which fertile land becomes desert
- The study of desert wildlife
Desertification affects about 3.2 billion people worldwide. Every year, the world loses 12 million hectares of productive land to desertification and drought — an area the size of England.
4. The Sahara Desert is roughly the same size as which country?
- United States
- India
- Russia
- Australia
The Sahara covers about 9.2 million square kilometres, close to the area of the entire United States (9.8 million). Remarkably, only about 5,000 years ago the Sahara was green savanna with rivers and lakes.
5. What is a desert varnish?
- A mirage effect on flat ground
- A dark coating on exposed rock surfaces in arid regions
- A type of cactus sap
- Sand polished to a shine by wind
Desert varnish is a thin, dark layer of manganese and iron oxides that forms on rocks over thousands of years. Ancient peoples carved petroglyphs by chipping through the varnish to reveal lighter rock beneath.
6. Which animal can survive the longest without drinking water?
- Kangaroo rat
- Thorny devil lizard
- Fennec fox
- Dromedary camel
Kangaroo rats can survive their entire lives without ever drinking water. They obtain all the moisture they need from metabolising dry seeds, and their kidneys are so efficient they produce urine five times more concentrated than human urine.
7. What is the driest place on Earth?
- Atacama Desert, Chile
- Dasht-e Lut, Iran
- Death Valley, USA
- McMurdo Dry Valleys, Antarctica
The McMurdo Dry Valleys have received virtually no rain or snow for approximately 2 million years. The katabatic winds that sweep through at up to 320 km/h evaporate all moisture. They are used by NASA to simulate Mars conditions.
8. What is the Great Green Wall project?
- An 8,000 km belt of trees being planted across Africa
- A massive solar panel installation in the Sahara
- A chain of oasis conservation sites
- A seawater desalination pipeline
The Great Green Wall stretches from Senegal to Djibouti across 11 countries. When complete, it will be the largest living structure on Earth. By 2030, it aims to restore 100 million hectares of degraded land.
9. What temperature was recorded at Death Valley in 1913, often cited as the highest air temperature ever measured?
- 52.0 degrees C
- 60.1 degrees C
- 56.7 degrees C
- 49.4 degrees C
The 56.7 degrees C (134 degrees F) reading at Furnace Creek, Death Valley, on July 10, 1913, remains the official world record, though some climatologists dispute its accuracy. Ground surface temperatures in deserts can exceed 80 degrees C.
10. What is an oasis?
- A sand whirlpool
- A type of desert storm
- A rocky desert plateau
- A fertile area in a desert where water is found
Many oases are fed by underground aquifers that can carry water from rainfall hundreds of kilometres away. The Siwa Oasis in Egypt has been continuously inhabited for over 12,000 years.
11. Which desert plant can live for over 1,000 years and has only two leaves?
- Welwitschia
- Saguaro cactus
- Joshua tree
- Baobab
Welwitschia mirabilis, found only in the Namib Desert, produces just two leaves that grow continuously and split over time. Some specimens are estimated to be over 2,000 years old. Charles Darwin called it 'the platypus of the plant kingdom.'
12. What causes a mirage in the desert?
- Dust particles scattering sunlight
- Reflection off sand crystals
- Hallucination from dehydration
- Refraction of light through layers of hot and cool air
Mirages are real optical phenomena, not hallucinations. Hot air near the ground bends light rays upward, making the sky appear to be reflected on the ground — which the brain interprets as water.
13. How much of the Sahara Desert is actually covered by sand dunes?
- About 5%
- About 25%
- About 50%
- About 75%
Most of the Sahara is rocky plateau (hamada), gravel plains (reg), and dry valleys. The vast sand seas (ergs) that most people picture make up only about a quarter of its area. Some dunes reach 180 metres tall.
14. What is the name of the fog-basking beetle that collects water from fog in the Namib Desert?
- Goliath beetle
- Stenocara gracilipes
- Dung beetle
- Scarab beetle
This beetle stands on its head facing into fog-laden wind. Water condenses on bumps on its back and rolls down channels into its mouth. Engineers have copied this design to create water-harvesting materials for arid regions.
15. Which river flows through the world's largest hot desert but never dries up?
- The Nile
- The Zambezi
- The Congo
- The Niger
The Nile flows for over 1,600 km through the Sahara without a single tributary joining it. It survives because of massive water volumes from equatorial Africa. Ancient Egyptians called it 'Iteru', meaning 'great river.'