有名言說：“這世界上本沒有路，走的人多了，也就成了路。”不論是人類還是動(dòng)物，都會(huì)在這個(gè)世界上留下自己的足跡。那么究竟是誰、在哪兒踏出了這世界上的“第一步”呢？

    Scientists believe they have uncovered Earth's oldest known footprints in the mountains of Nevada（美國內(nèi)華達(dá)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（原生動(dòng)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（埃迪卡拉紀(jì)）, before the Cambrian（寒武紀(jì)） period "explosion." During the Cambrian complex animals rapidly emerged and replaced simple multicellular（多細(xì)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、沉積物） 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.