What scientists think is that the earth
科学家们认为地球
was different because of the arrival of
是不同的是因为在它的表层的水里面长有的小植物.
small plants growing in the water on its surface.Nobody understood that these plants were the start of many changes.
没有人曾认识到这些植物正是许多变化的开始.
They multiplied and filled the first oceans and seas with oxygen.
它们不断繁衍给最初的海洋提供氧气.This encouraged the development of early shellfish and all sorts of fish.这促成了早期海贝和各种鱼类的发展.
Mary（Many） millions of years later the first green plants began to appear on land.数百万年以后这些早期绿色植物开始出现在陆地上.Scientists believe that taking carbon dioxide from the atmosphere and filling the air with oxygen helped life to develop.科学家们相信植物从大气中吸取大氧化碳又向空气中释放氧气帮助生命发展.Later land animals appeared.陆地动物随后出现了.Some were insects.他们中有些是昆虫.Others,called amphibians,were able to live on land as well as in the sea.还有一些被称为两栖动物,它们既能生活在陆地上也能生活在海洋里.When the plants grew into forests,reptiles appeared from the first time.当这些植物长成了丛林,爬行动物首次出现了.They produced young generally by laying eggs.它们通过产卵繁衍后代.Later,some huge animals,called dinosaurs developed.后来,出现了一些被称为恐龙的巨型动物.They laid eggs,too.它们也是产卵的.They became the most important animals on the earth for millions of years.在数百万年的时间里,它们成了地球上最重要的动物.But when they disappeared,mammals became more important.但是当他们渐渐消失的时候,哺乳动物变得更加重要了.They were the last group of animals and they were different because they produced their young from within their bodies.它们是最后一群动物,它们与其他动物不同的是它们通过分娩繁衍后代.
Small clever animals,now with hands and feet,appeared and spread all over the earth.后来出现的小巧的聪明的动物,现在长有手和脚,遍及地球各个角落.They developed new methods of growing food,hunting and moving around.他们发展了新的方法来种植食物、狩猎和迁徙.As time went by they covered the earth and have become the most important animals on the planet.随着时间的推移,他们遍布地球,现在已经成为这个星球上最重要的动物.But they are not taking care of the earth very well.但是他们却没有很好的照看地球.They are putting too much carbon dioxide into the atmosphere,which prevents heat from escaping from the earth into space.他们朝大气层中投放了太多的二氧化碳,含有太多二氧化碳的大气层使热量不会从地表散发到空中.The earth may become too hot for the lives on it.地球很可能变得太热而不适合生物在上面生活.Whether life will continue on the earth for millions of years to come will depend on whether this problem can be solved.地球上的生命是否会持续数百万年取决于这个问题能否得以解决.