Earth's formation began about 4.6 billion years ago. Our planet started as part of a giant molecular cloud - a vast collection of gas and dust particles floating in space. This cloud contained all the materials that would eventually become our solar system, including Earth.
The molecular cloud was unstable and began to collapse under its own gravity. As the cloud collapsed, it started spinning faster due to conservation of angular momentum. The collapsing material flattened into a disk shape, with most of the mass concentrating at the center to form what would become our Sun.
在原始行星盘内，微小的尘埃颗粒开始通过碰撞和静电力相互粘连。这些小团块逐渐长大，形成了我们所称的星子——直径从几公里到数百公里的岩石天体。这种吸积过程是行星形成的第一步。
星子通过引力吸引和碰撞逐渐合并，最终形成了原始地球。早期的地球是一个炽热的熔融球体，温度极高。在这个过程中，较重的物质如铁和镍下沉到中心形成地核，较轻的物质上浮形成地幔和地壳，这个过程称为分异作用。
地球的原始大气主要通过火山活动释放的气体形成，包括水蒸气、二氧化碳和其他气体。地球上的水主要来自富含冰的彗星和小行星的撞击。随着地球表面温度的降低，水蒸气凝结形成了最初的海洋。这样，地球逐渐具备了支持生命的基本条件。