Between 20 and 40 per cent of planet Earth is covered in grasslands, across every continent except for Antarctica. Grass is a low-growing, flowering plant with groups of narrow leaves growing from its base. Strong roots typically hold this plant's leaves firmly to the ground.
One of the most common sights along stretches of grass is grass-eating animals. This is because many large animals rely on extensive grasslands to survive, and grass grows well with this regular trimming (修剪). The plants gain their energy from sunlight and require healthy cells to do so. If the leaves aren't cut, the tips die and start to rot. When they are damaged with a clean cut, however, the cells are caused to grow quicker and produce new, healthy tissue. This is also why cutting your garden's grassland regularly can make your grass look thicker and healthier.
Humans rely on grass for food, too. Many grasses, such as w heat or corn, are harvested as a main part of some diets. Meanwhile, grass is used indirectly to produce food in the form of livestock (牲畜). Cattle farmers require grass in their fields to feed cows and sheep before they are turned into meat for human consumption.
One of the most debated questions is how long ago grass evolved. Because grass doesn't preserve well as a fossil, a definitive answer is hard to come by. Until recently, many scientists estimated that grass began to grow on Earth between 50 and 65 million years ago.
However, within the last decade, a piece of 100-million-year-old amber (琥珀) was found that appeared to contain the oldest grass fossil to date. Studies of fossilized dinosaur faces (粪便) also suggest that some dinosaurs lived at the same time that grass grew on the planet, incorporating it into their diets.