Yours,

Li Hua

5 . Walk through the Amazon rainforest today and you will find it is steamy, warm, damp and thick. But if you had been around 15,000 years ago, during the last ice age, would it have been the same? For more than 30 years, scientists have been arguing about how rainforests like the Amazon might have reacted to the cold, dry climates of the ice ages, but until now, no one has reached a satisfying answer.

Rainforests like the Amazon are important for mopping up CO₂ from the atmosphere and helping to slow global warming. Currently the trees in the Amazon take in around 500 million tons of CO₂ each year: equal to the total amount of CO₂ giving off in the UK each year. But how will the Amazon react to future climate change? If it gets drier, will it still survive and continue to draw down CO₂ ?

Scientists hope that they will be able to learn in advance how the rainforest will manage in the future by understanding how rainforests reacted to climate change in the past. Unfortunately, getting into the Amazon rainforest and collecting information are very difficult. To study past climate, scientists need to look at fossilized pollen, kept in lake mud. Going back to the last ice age means drilling deep down into lake sediments （沉淀物）which requires specialized equipment and heavy machinery. There are very few roads and paths, or places to land helicopters and aeroplanes. Rivers tend to be the easiest way to enter the forest, but this still leaves vast areas between the rivers completely unsampled（未取样）.So far, only a handful of cores have been drilled that go back to the last ice age and none of them provide enough information to prove how the Amazon rainforest reacts to climate change.

6 . How fit are your teeth? Are you lazy about brushing them? Never fear: An inventor is on the case. An electric toothbrush senses how long and how well you brush and it lets you track your performance on your phone.

The Kolibree toothbrush was exhibited at the International Consumer Electronics Show in Las Vegas this week. It senses how it is moved and can send the information to an Android phone or iPhone via a Bluetooth wireless connection.

The toothbrush will be able to teach you to brush right (don’t forget the insides of the teeth!) and make sure you’re brushing long enough. “It’s kind of like having a dentist actually watch your brushing on a day-to-day basis,” says Thomas Serval, the French inventor.

The toothbrush will also be able to talk to other applications on your phone, so developers could, for example, create a game controlled by your toothbrush. You could score points for beating monsters among your teeth. “We try to make it smart and fun,” Serval says.

Serval says he was inspired by his experience as a father. He would come home from work and ask his kids if they had brushed their teeth. They said “yes,” but Serval would find their toothbrush heads dry. He decided he needed a brush that really told him how well his children brushed.

The company says the Kolibree will go on sale this summer, from $99 to $199, and the U.S. is the first target market.