Please do not be vague in your inquiries. The claimed discovery of evidence of past Martian life in a rock ejected from Mars, which subsequently fell to Earth in Antartica and was collected as meteorite Alan Hills 84001. The discovery of extrasolar planets. And so on.
Accretion still occurs today, but at a much, much slower rate than in the distant past.
Physical evidence at this boundary is strongly suggestive of the impact of a 10 km asteroid upon the Earth. This impact is hypothesized to have resulted in the extinction of a large number of organisms, most notably, the dinosaurs.