简单地说,生活没有任何的困难部分进化而来。这适用于元古代世界各地,不仅在印度。石化的缓慢替代有机组织与矿物质。死生物非常罕见的条件下变成化石。“硬”通常意味着组织已经矿化。例如,(脊椎动物)(骨)(https://en.wikipedia.org/wiki/Bone)或(软体动物或brachiopod)(壳)(https://en.wikipedia.org/wiki/Exoskeleton)是由方解石和霰石。这个材料是耐用的地质时间,所以有时间被其他矿物质通常慢慢取代。海绵骨针(https://en.wikipedia.org/wiki/Sponge_spicule)可以由硅,和可以不变。(寒武纪)(https://en.wikipedia.org/wiki/Cambrian)是最早的时候我们发现的化石动物艰难的部分。不同类型的生物矿化的部分有差异,所以我们现在最好的解释是,许多生物在寒武纪期间独立开发的矿化部分。 Fossils of soft tissue can be found, but since it decomposes rapidly, these fossils are preserved by different processes. Although they can often leave some of their original atoms behind as a [layer of carbon](https://en.m.wikipedia.org/wiki/Carbonaceous_film_(paleontology)), it's often just an [impression](https://ucmp.berkeley.edu/paleo/fossilsarchive/impres.html). Sometimes the presence of a lifeform has to be deduced from a [trace fossil](https://en.wikipedia.org/wiki/Trace_fossil) such as a worm burrow. Soft tissue fossils are typically only preserved in very fine-grained sediment such as mudstone. Think about how much better a picturre looks on a high-resolution screen than a lower resolution one. As [Wikipedia](https://en.wikipedia.org/wiki/Lagerst%C3%A4tte) 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](https://en.wikipedia.org/wiki/Stromatolite) 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](https://en.wikipedia.org/wiki/Ediacaran) (or sometimes [Vendian](https://ucmp.berkeley.edu/vendian/vendian.html)) starting 650 million or so years ago. These include the famous [Ediacaran biota]( https://en.wikipedia.org/wiki/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](https://pubs.geoscienceworld.org/gsa/geology/article-abstract/40/4/307/130842/The-advent-of-hard-part-structural-support-among?redirectedFrom=PDF) 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.