If time travel machines existed and allowed for travel back in time one million years ago, it would likely be an incredibly dangerous endeavor for several reasons:
Environmental Hazards: The Earth's environment and climate were significantly different one million years ago. There were different geological formations, different atmospheric conditions, and different ecosystems. Humans would likely struggle to survive in such an environment without proper equipment, resources, and adaptations.
Biological Hazards: One million years ago, the Earth was inhabited by different species, including extinct megafauna, different types of plants, and possibly even early hominids. Interacting with these ancient organisms could pose serious risks, including the potential for unfamiliar diseases, predators, or territorial conflicts.
Temporal Paradoxes: Time travel, especially to the past, raises complex paradoxes and causality issues. Interacting with the past could inadvertently alter the course of history, leading to unpredictable and potentially disastrous consequences for the present or future. Small changes could have significant ripple effects, potentially leading to paradoxes and contradictions.
Technological Limitations: Time travel itself, if achievable, would likely require advanced and highly complex technology. The operation and control of such technology could present significant risks and challenges, including malfunctions, unintended consequences, or the inability to return to the present time.
It's important to note that the topic of time travel remains purely speculative at present, and the hazards mentioned above are based on hypothetical scenarios. As of now, our understanding of the laws of physics and the nature of time does not provide a framework for practical time travel.