Early Plants and Animals
The first plants on Earth were blue-green algae. These appeared about 3.5 billion years ago.
The first spiders appeared 400 million years ago. The first ferns grew 300 million years ago. The first dinosaurs appeared 230 million years ago.
Most species change over time.
When the Tyrannosaurus first appeared about 98 million years ago, they were the size of Labrador dogs. But it grew bigger and bigger. Some 30 million years later, the T-rex was 12 metres long and had teeth between 15 and 30 centimetres long.
Not all species change. Ginkgo trees, Coelacanth fish, and crocodiles are almost the same as they were millions of years ago. Because of this they are nicknamed 'living fossils'.
Can you think why living fossils are just like their ancestors?
True or false?
Spiders appeared before dinosaurs.
The T-rex grew smaller over time.
Living fossils haven't changed over millions of years.
Find words that mean: well-known, find out, look into
The Coelacanth (pronounced 'SEAL-ah-canth') is the most famous living fossil in the world. This fish first appeared about 350 million years ago.
The Coelacanth grows to 2m long and can weigh 80 kilograms. It lives more than 90m down in the ocean - in water where there is no sunlight. The Coelacanth can live 100 years. Many people thought the Coelacanth died out 65 million years ago. But in 1938 scientists discovered Coelacanth were living in the sea off the coast of South Africa.
When scientists investigated, they found local fishermen had been eating Coelacanth for many years.
Since then another type of Coelacanth has been found off Sulawesi in Indonesia. The South African fish is blue but the Indonesian one is brown.
You don't need to go far to see some living fossils.
The first crocodiles appeared about 200 million years ago. And they haven't changed much since then. To see these living fossils, visit the Chinese alligators at Hong Kong Zoo and Botanical Garden. Then there's Hong Kong's celebrity crocodile, Pui Pui, who is being well taken care of at the Wetlands Park in Tin Shui Wai.
Hong Kong also has three old and valued Gingko trees. The first Gingko trees appeared 270 million years ago. Most species died out about 1.8 million years ago, but the Gingko trees on the mainland survived. Look for Gingko trees in Chater Garden, Jockey Club Tak Wah Park and Sha Tin Park.
Alternatively, go snorkelling and look out for Nautilus. These pretty little molluscs first appeared 542 million years ago.
If you're on the beach searching for horseshoe crabs, you can also look for empty Nautilus shells. They make nice jewellery.
Choose the correct alternative:
Horseshoe crabs have remained unchanged since the Jurassic Period (208 to 144 million years ago).
Despite their name, these ancient animals aren't crabs. Horseshoe crabs are close relatives of/in spiders and scorpions.
You can see horseshoe crabs on/up mud flats near rivers and the beach. They hunt worms and thin-shelled molluscs like soft-shelled crabs.
Although they have survived for millions of years, scientists are worried that horseshoe crabs are now on/in danger.
Pollution is killing baby crabs. Also, pregnant female crabs with eggs are a popular food by/in Asia. Too many are caught and eaten.
So, if you see one, take a picture and leave it alone.
Big Planet, Big Life
Fill in the blanks: species, extinct, habitats
Species change because they adapt to different _________. Even small differences can be very important.
For example, the African elephant and the Asian elephant look similar because they have a common ancestor. But, as they live in different places, these animals evolved differently. They still look similar but they are now different _______.
Billions of years ago, the only life forms on Earth were bacteria. Today there are between 5 to 100 million living species.
As habitats change, some species become _________ and new species appear. Scientists believe most species exist for about 10 million years and then die out.
That means 99.9 per cent of all species that have ever lived are now extinct.
now do this
Answer the following questions without referring to the text. If you can't remember the details, read the article again.
1. Which appeared first?
2. Living Coelacanth were found . . .
a. in the ocean off South Africa
b. in the mountains of Nepal
c. in Modaoxi, China
3. What living fossil is at Sha Tin Park?
a. Chinese alligators
b. Gingko trees
c. horseshoe crabs
4. Horseshoe crabs live . . .
a. on mud flats
b. in the forest
c. in the mountains
5. Almost all the dinosaurs died out . . .
a. about 400 million years ago
b. about 180 million years ago
c. about 65 million years ago
6. The Nautilus is a type of . . .
Everyone thought dawn redwood trees died out 23 million years ago. But living dawn redwood trees were discovered in Modaoxi, China in 1944
Every now and again a big change on Earth kills off almost all life. About 65 million years ago, almost all the dinosaurs died out. Similar mass extinctions have happened four other times in the past 540 million years
The first Gingko trees appeared 270 million years ago. The first modern humans appeared about 200,000 years ago
True or false: T, F, T Fill in the blanks: habitats, species, extinct
Synonyms: famous, discover, investigate
Correct alternative: of, on, in, in
Quiz: 1. b, 2. a, 3. b, 4. a, 5. c, 6. a