If you look at all the traits animals and plants have, there are correlations and patterns unrelated to the environment, consistent only with a pattern of descent with modification.

For example, all the animals that produce milk also have fur, while all the animals with beaks and hollow bones also have feathers.

These groups of correlated organisms are found regardless of their environment, so penguins have all the bird traits even though they live in the ocean, seals have all the mammal traits even though they live in the ocean.

This pattern only has one consistent explanation: life on earth is a result of descent with modification: evolution.