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有名言说：“这世界上本没有路，走的人多了，也就成了路。”不论是人类还是动物，都会在这个世界上留下自己的足迹。那么究竟是谁、在哪儿踏出了这世界上的“第一步”呢？
Scientists believe they have uncovered Earth's oldest known footprints in the mountains of Nevada（美国内华达州）—a fossil find that suggests animals have been walking around about 30 million years longer than previously thought, according to new research.
The controversial tracks—described by one skeptical scientist as "paired rows of dots"— may indicate animals had legs in the late Protozoic（原生动物的） era, about 570 million years ago, according to lead researcher Loren Babcock.
The discovery is the strongest evidence to suggest animals were able to move about on their own appendages during the Ediacaran period（埃迪卡拉纪）, before the Cambrian（寒武纪） period "explosion." During the Cambrian complex animals rapidly emerged and replaced simple multicellular（多细胞的） animals, said the Ohio State University professor.
About 570 million years ago, the area was covered by a shallow sea. The water had a mat-like surface made of sediment（沉淀物、沉积物） grains that were held together by a cohesive network of bacteria and fungi, which would have easily preserved animal tracks.
The tracks were determined to have been made in the Ediacaran period by comparing the "footprints" layer to previously dated layers with similar features.
