一块可追溯到8.9亿年前的海绵化石，这可能是迄今为止发现的最古老的动物。虽然并非所有研究人员都相信，上面留下的标记是来自动物的，但如果是真的话，这可以让我们深入了解最早动物的进化。
These wiggly lines could be the oldest fossil animal ever discovered.
While they may look like random markings on a rock, if these are the remains of an ancient animal, it would push the first physical evidence of animals on this planet back by 300 million years.
Animals are multicellular eukaryotes – complicated lifeforms, that consume organic material, breathe oxygen and live now as the varied and complex creatures we see all around us.
But their earliest ancestors likely started small and kept things pretty basic.
They might have even been a sponge.
Okay, not quite like that, but sea sponges are a kind of organism still in existence today whose close relatives are a good candidate for early animals.
That's because they have simple body plans – essentially tube-like structures that filter feed – and they have relatively few types of cell.
But determining if sponges were the first kind of animal has been tricky.
The earliest fossils that scientists are relatively sure are animals come from around 550 million years ago, just before the Cambrian explosion.
Older fossils have been quite contentious, as it's hard to work out what's an animal and what's not.
