The first living things on Earth, single-celled micro-organisms or microbes lacking a cell nucleus or cell membrane known as prokaryotes, seem to have first appeared on Earth almost four billion years ago, just a few hundred million years after the formation of the Earth itself.
No system is closed off by it surroundings.
Answer:
Fossils of Ambulocetus
Explanation:
Fossils of Ambulocetus show that it was about 3 meters long. It had hind legs which were more suited for swimming than for walking. It could hear very well under water, and its teeth resembled those of modern cetaceans. Its limb anatomy suggests that it was slow on land and in the water.
No, because the immune system is already battling with the virus or disease
