根据Ravindra Kumar的Historical Geology and Stratigraphy >，元古代早期的生命形式由于缺乏坚硬的部分，不能作为化石保存下来。除此之外，< strong>Kumar还指出，

随着硫、硫化氢、二氧化碳等有毒物质的去除，元古代沉积盆地中藻类等生命形式蓬勃发展。

我已经多次尝试寻找任何可能的答案，但无法找到任何令人满意的。如果有人对这个问题有想法，请试着回答。

提前感谢。

寒武纪是我们在任何地方发现硬体动物化石的最早时间。不同生物的矿化部分各不相同，所以我们目前最好的解释是，在寒武纪，许多生物独立地发展了矿化部分。

可以发现软组织化石，但由于软组织分解迅速，这些化石被不同的过程保存。虽然它们通常可以留下一些原始原子作为碳层，但它通常只是一个印象。有时，生命形式的存在必须从一个蛛丝马迹的化石中推断出来，比如一个蠕虫的洞穴。

软组织化石通常只保存在非常细粒度的沉积物中，如泥岩。想想看，一张照片在高分辨率的屏幕上比在低分辨率的屏幕上好看多了。

As Wikipedia says:

These formations may have resulted from carcass burial in an anoxic environment with minimal bacteria, thus delaying the decomposition of both gross and fine biological features until long after a durable impression was created in the surrounding matrix.

For most of the Proterozoic, all we find are stromatolites caused by bacterial mats capturing particles of sediment. There are hints of multicellular life from the mid-Proterozoic usually interpreted as impressions of algae. But the most unambiguous fossils of multicellular life appear in a period at the end of the Proterozoic called the Ediacaran (or sometimes Vendian) starting 650 million or so years ago. These include the famous Ediacaran biota from Australia, which give the period its name. But trace fossils and what appear to be early bilaterians appear as well.

Anyway, none of them contain hard parts. This paper hints that the evolution of hard parts similar to sponge spicules may have been starting in the Ediacaran biota, but it's unclear if any of those organisms are the ancestors of anything that came later.