4 . Ancient builders across the world created structures that are still standing today, thousands of years later. Roman builders built thick concrete sea barriers against waves. Mayan builders created great sculptures, and Chinese builders constructed walls against foreign enemies.

A growing number of scientists have been studying materials since a long time ago. They are breaking apart pieces of buildings and reading historical texts hoping to learn how they have stood for thousands of years. The research has turned up a surprising list of materials that were mixed into old buildings. They include tree bark, volcanic ash, rice and beer. These unexpected materials can have the ability to get stronger over time. Figuring out how to copy these features can have real impacts today. While some of our modern concrete has the strength to hold up very tall buildings and heavy structures, it cannot compete with the durability of these ancient materials.

Many scientists have turned to the Romans. Starting around 200 BC, the Roman Empire was building concrete structures that have stood the test of time. Even in places where seawater has been hitting structures for ages, you will find concrete basically the way it was when it was poured 2,000 years ago. They think they have found an important reason why some Roman concrete has held up structures for thousands of years. That the ancient materials have an unusual power to restore themselves and “cure” cracks (裂缝) when they form is the most shocking for them. Exactly how is not yet clear, but scientists are starting to find the reasons.

Today’s builders cannot just copy the ancient processes. Even though Roman concrete lasted a long time, it couldn’t hold up heavy buildings. Instead, researchers are trying to take some of the ancient materials and add them into modern mixes. People don’t need to make things last quite as long as the Romans did. If we add 50 or 100 years to concrete’s lifespan, we’ll surely require less pulling down, less maintenance and less material in the long run.

7 . Ancient builders across the world created structures that are still standing today, thousands of years later. Yet the concrete that makes up much of our modern world has a lifespan of around 50 to 100 years. A growing number of scientists have been studying materials from long-ago eras, hoping to uncover how they’ve held up for millennia.

Many researchers have turned to the Romans for inspiration. Starting around 200 BCE, the architects of the Roman Empire were building impressive concrete structures that have stood the test of time. Even in harbors, where seawater has been battering structures for ages, you’ll find concrete basically the way it was when it was poured 2,000 years ago. Most modern concrete starts with Portland cement, a powder made by heating limestone and clay to super-high temperatures and crushing them. That cement is mixed with water to create a chemically reactive paste. Then, blocks of material like rock and gravel are added, and the cement paste mixes them into a concrete mass. According to records from ancient architects, the Roman process was similar. The ancient builders mixed materials like burnt limestone and volcanic sand with water and gravel, creating chemical reactions to stick everything together.

In a study published earlier this year, Admir Masic, a civil and environmental engineer, proposed that this power comes from blocks of lime that are scattered throughout the Roman material instead of being mixed in evenly. Researchers used to think these blocks were a sign that the Romans weren’t mixing up their materials well enough. Instead, after analyzing concrete samples from Privernum—an ancient city outside of Rome — the scientists found that the blocks could fuel the material’s “self-healing” abilities. When cracks form, water is able to flow into the concrete, Masic explained. That water activates the leftover lime, leading to new chemical reactions that can fill in the damaged sections.

The ancient architectures suggested using extracts from local chukum and jiote trees in the lime mix. When researchers tested out the recipe, they found the resulting plaster was especially durable against physical and chemical damage.

Studies have found all kinds of natural materials mixed into structures from long ago: fruit extracts, milk, cheese curd, beer, even dung and urine. The paste that holds together some of China’s most famous structures—including the Great Wall and the Forbidden City — includes traces of sticky rice.

“Some of these ancient builders might have just gotten lucky”, said Cecilia Pesce, a materials scientist at the University of Sheffield in England, “They’d throw just about anything into their mixes, as long as it was cheap and available.”

Today’s builders can’t just copy the ancient recipes. Even though Roman concrete lasted a longtime, it couldn’t hold up heavy loads: “You couldn’t build a modern skyscraper with Roman concrete,” Cecilia said. “It would collapse.” Instead, researchers are trying to take some of the ancient material’s specialties and add them into modern mixes.

8 . Great! You finally have a long holiday during which you can get to that corner of the world you’ve always wanted to visit. However, to make sure your trip goes as smoothly as you want, you need to make some preparations. Here are the steps you need to take to prepare for your trip.

Choose a destination

You can’t plan a trip when you’re not sure where you want to go.     1     Choose a place you want to visit and plan your vacation around it.

Budget

    2     Research the cost of your destination including transportation, hotels, food and drinks. You can save money by traveling during the off-season. Prepare a little more money than you might need, just in case.

    3    

Depending on your vacation destination, you might need some important documents such as a valid passport and visa. Make sure your passport hasn’t expired and if you don’t have one, apply in time, as visa applications are often a complex process that can take weeks to be approved.

Consider travel insurance

A car accident lawyer in Vancouver would advise you to take out travel insurance because it’s more than just medical protection.     4     You can also buy overseas medical insurance because it can help you prepare for the worst.

Book your flight and accommodation

Booking the flight and accommodation should be one of the first things you should do. Book your flight months in advance because it’s more economical and you can save a lot of money.     5    

9 . When I first set foot in Western Australia’s Pilbara, a landscape holding 3.5-billion-year-old clues to the beginning of life, I was very disappointed. The year was 1994. I drove excitedly out of the west coast town of Port Hedland, but all I saw for the first 150 kilometers were a few dead trees and smoky dust across the burnt, flat plain. And the heat!! I’d never experienced anything this terrible before. Or breathed air so thick with biting flies.

But as we continued to head south on the highway to. Marble Bar—the hottest town in Australia—some low, broad hills started to rise from the horizon. As we continued down a dirt track into the hills, the burnt plains gave way to grass-covered hills. This grass is called spinifex, an amazing but cruel creation. It grows as bushes up to one meter in diameter (直径), with round, fine leaves with needle-sharp tips. The tips will go through just about any piece of cloth. My guide wore thick gaiters (护腿) to protect his legs. But he had failed to inform me of the risk. Without any gaiters, my skin was covered with needle tips that remained in my legs for months.

The land, ultimately, proved worth the discomfort. Here I was walking over some of Earth’s oldest, best-preserved rocks that contain evidence of life from almost the very beginnings of time on our planet.

This area had changed much from when it was first formed 3.5 billion years ago. Back then it would have been a black volcanic land, with no color from vegetation. Over the hills I might have seen a green, iron-rich sea under an orange sky heavy with carbon dioxide and without oxygen. Several billion years after that, the world would turn cold and become covered in a global ice sheet, destroying almost every living thing. When it melted away, oxygen levels rose again. Life really got going. Animals slowly occupied the land, so did new types of plants. The greening of our planet began, and a wide variety of organisms (有机体) appeared including. unfortunately for me, spinifex.