What two developments freed animals to roam and inhabit the earth?

It's impossible to pinpoint two specific developments that "freed" animals to roam and inhabit the earth. The evolution of life and the diversification of animal species is a complex process that unfolded over billions of years, driven by many interconnected factors.

However, two significant milestones in this process were:

1. The evolution of multicellularity: This event, estimated to have occurred around 2.1 billion years ago, allowed organisms to become larger and more complex, leading to the development of specialized tissues and organs. This paved the way for the emergence of animals as we know them.

2. The Cambrian Explosion: This period of rapid diversification of life, roughly 541 million years ago, saw the explosion of new animal forms and body plans. This was likely driven by factors like increased oxygen levels, the development of predatory-prey relationships, and the evolution of hard body parts like shells.

While these two events are critical in understanding the development of animal life, it's crucial to remember that they are just two points in a long and intricate evolutionary journey. The process of animals inhabiting the earth continues today, with new species evolving and adapting to ever-changing environments.