Ancient green land

Copenhagen University: 5-Jul-2007 14:00 Eastern US Time

The world's oldest DNA has shown that ancient Greenland was once covered in conifer forest and had a mild climate.

Eske Willerslev is an expert in extracting DNA from organisms buried in permafrost. He is a professor at Copenhagen University.

Willerslev has been analysing DNA from beneath Greenland's kilometre-thick icecap. The DNA is close to half a million years old. The results have just been published in the journal Science.

Ten percent of the Earth's surface has been covered with ice for thousands of years, hiding what lies beneath. But scientists have been drilling through the icecap to collect complete columns of ice from top to bottom.

This ice contains yearly layers and is a frozen archive of the world's climate.

Eske Willerslev began to wonder if there might also be DNA buried deeply. If so then perhaps he could reconstruct the living environment of ancient times.

Ice-core samples

The lower parts of the icecap are mixed with mud from the bottom, which is what Willerslev was interested in. So he obtained base layer samples from three drillings. The first two were DYE-3 from the south of Greenland and the GRIP drilling from the middle of the Greenland ice sheet.

The third core came from the John Evans glacier in Canada. This is only a few thousand years old. These samples were used to test the methods.

From the Canada samples Willerslev found DNA from three of the four most common plants that grow in the area. "That means that what one finds under the ice represents the local environment," he explains.

Greenland samples

In the sample from the GRIP drilling, the scientists found no DNA remains at all. Not from plants, mammals or insects. The explanation, says Willerslev, is that the ice in the middle of the ice sheet is over three kilometres thick.

"The greater pressure produces a higher temperature at the base, and so the DNA material, which cannot tolerate warmth, disintegrates."

But at the DYE-3 drilling site the ice is 'only' two kilometres thick. Here the scientists found DNA so well preserved that traces of a long list of plants and insects could be found. These included pine, spruce, alder and yew trees.

There were also remains of flies, butterflies and moths that once flew and fluttered among the Greenland woodland. Traces of beetles and spiders were also found.

These results prove for the first time that there were forests full of life in south Greenland

The genetic material is telling a story of a living environment completely different from what we see today, says Willerslev. "We have found grain, pine, yew and alder. These correspond to the landscapes we find in Eastern Canada and in the Swedish forests today."

The scientists can also tell what the climate was like at the time. This is because each tree species has its own temperature needs. "The yew trees reveal that the temperature during the winter could not have been lower than minus 17 degrees Celsius," says Willerslev

Traces of other trees show that the summer temperatures were at least 10 degrees Celsius.

Dating

The scientists used the genetic traces of butterflies, moths, flies and beetles, to analyse their mitochondria. These contain small pieces of DNA that change with time in a regular way. This means they can be used like a clock to date the DNA.

The team also analysed the insects' amino acids, which also change over time. Both dating methods suggest that the insects were at least 450,000 years old.

The dating of the samples remains uncertain. But the DNA has been preserved under ice for at least 130,000 years, and perhaps up to 1 million years, say the scientists.

More help with words

average

breed

cell

conception

fertile

fertilisation

genes

individual

inherit

molecule

permanent

sperm

subsoil

temperature

What's it all about?

1. Scientists have discovered that something once covered Greenland. What was that?
2. What have the scientists found out about the climate there?
3. What is special about the DNA they used to make these new discoveries?
4. How thick is Greenland's icecap?
5. How old is the DNA the scientists have found beneath the icecap?
6. What have scientists been doing to collect complete columns of ice?
7. Each year more snow falls, so each year a new layer is laid down on the icecap. What does the writer of the article call these layers?
8. The scientists studied samples from how many different drilling sites?
9. Where were these sites?
10. The Canada samples were used to test that DNA from drillings was actually DNA from the ----- environment.
11. The two sets of Greenland drillings gave very different results. What were they?
12. What reason do the scientists suggest for the result at the GRIP drilling site?
13. State six of the living things the scientists found traces of at the third drilling site.
14. What do these results prove for the first time?
15. The results are telling a story of a living ----------- on Greenland much different from the solid icecap that exists there today.
16. What else can the scientists tell about Greenland at the time the trees were alive?
17. In one sentence how can they do that?
18. When were the insects the scientists found traces of actually alive?
19. Willerslev wondered if there was ancient DNA under the ice. If there was he could use it to "reconstruct the living environment" of long ago. In one sentence and your own words what does "reconstruct the living environment" mean?
20. Find a sentence in the story that says what the aim of this work was.
21. Find a sentence or phrase in the story that is a hypothesis.
22. Find a sentence or phrase in the story that is evidence for a hypothesis.
23. If you were these scientists what question would you still have about any of this?
24. Can you think how you might try to answer that question?

More activities for this story

Ancient green land UK US

Topic for discussion, research or pupil presentations

A) In the popular film Ice Age the intrepid heroes meet a whole army of dodos, the flightless bird that went extinct in the 17th century (not during the Ice Age at all but who’s counting?).

These are portrayed as hilariously stupid, headstrong and clumsy birds, which manage to extinguish themselves at every opportunity by crashing into each other, falling off cliffs into diving into molten lava.

While this makes for entertaining episodes, it is very unfair on the poor old dodo and totally misrepresents why species do go extinct. For a start any animal as suicidally stupid as the dodos in this film wouldn’t have evolved and survived in the first place.

In Ice Age 2, Manny the mammoth believes himself to be the last of his kind - until he meets a female mammoth who thinks she’s a possum (don’t ask - you need to see it).

Working in groups, students should choose a bird or animal that is now extinct, such as the dodo, mammoth, sabre-toothed tiger, and explore the various possible reasons for their extinction. They should deliver a presentation on the subject to the class.

The class should then try to find the feature common to all extinctions.

B) An interesting twist on the above is an in-depth lesson from Discovery School, with extension activities and recommended websites. This lesson looks at why particular species, known as living fossils, have survived into the present, when their contemporaries have long gone the way of 99.9% of all species that ever walked, crawled, swam or flew. Extinction is normal.

A nice aspect of the lesson is the following activity that aims to make the scientific method explicit in kids’ minds:

Before beginning the research, have students develop a hypothesis about why their animal did not become extinct. They should write their hypothesis on Part A of the sheet ... Students should base their hypotheses on the facts discussed during step 5, as well as the discussion about why dinosaurs became extinct. Below is a sample hypothesis explaining why coyotes might survive if conditions on Earth changed dramatically and other species were killed off.

Tips for science class discussions and groupwork


No 54

Many of our students are poor readers ... if they do not understand what they read, then school and reading simply become a source of frustration. I am teaching and coordinating our summer school program, which is primarily web based (LA and Math).

There is a ton of reading that these kids must do and many of them simply cannot do it - which is probably much of the reason they are in summer school to begin with. Being able to work one on one with these students has been an eye opening experience. This new perspective, coupled with
what I am learning from the reading course [the Florida On line Reading Professional Development], is causing me to become passionate about the belief that we all (teachers) must accept the responsibility of helping all students become better readers, regardless of our particular content. Many of the students I have been working with this summer are also some of our biggest discipline problems, which may result from the overwhelming frustration they encounter every day.

Extract from an online forum of the National Science Teachers Association by Tina Annucci, Gamble Rogers Middle School, St Augustine, FL