It's impossible to pinpoint an exact date for the first fossils, but the earliest known fossils date back to around 3.7 billion years ago. These are stromatolites, layered structures formed by the growth of microbial mats.

Here's a breakdown of the earliest fossil discoveries and their age:

* 3.7 billion years ago: Stromatolites in Greenland

* 3.5 billion years ago: Microfossils in Western Australia

* 3.4 billion years ago: Stromatolites in South Africa

It's important to note that:

* Fossil formation is a rare event. Only a tiny fraction of organisms are preserved as fossils.

* The early Earth was very different from today. The atmosphere and oceans were likely very different, and life was much simpler.

* The search for the first fossils continues. Scientists are constantly finding new and older fossils that push back the timeline of life on Earth.

So, while we don't know the exact moment the first fossils formed, we know that life on Earth has been present for at least 3.7 billion years, and likely even longer.