This thesis lies in the overlap of environmental political theory and environmental ethics. More specifically, it focuses on the intersection between distributive ecological justice (justice to nature), and environmental justice (distributing environmental goods between humans). Against the backdrop of the current sixth extinction crisis, I address the question of what constitutes a just usage of ecological space. I define ecological space as encompassing environmental resources, benefits provided by ecosystems and physical spaces and when considering its just usage I not only take into account claims to ecological space held by other humans but also the demands of justice with regards to nonhuman living beings such as animals and plants. In order to address my overall research question, I look at three areas of inquiry in particular. My first area of concern is questions around how environmental justice can be made compatible with a theory of ecological justice. Here I defend a specific definition of ecological space and provide a critique of theories of justice that are based on the view that humanity has an original ownership of the Earth. Secondly, I defend a biocentric approach to distributive ecological justice based on all living beings constituting together a community of fate, and I additionally clarify the relationship between justice and biodiversity loss. Lastly, considering that the current situation of life on Earth does not resemble the circumstance of moderate scarcity where all needs could theoretically be met (as usually assumed by the most influential theories of justice), I inquire into how demands of environmental and ecological justice differ in different circumstances of scarcity, and what could be considered a just compromise between these two domains of justice. I then apply these last considerations to the Half-Earth proposal for creating large protected areas for nonhuman species, which has been advocated by E. O. Wilson and other ecologists as a means to slow the current rate of anthropogenic species extinctions. In essence, the Half-Earth proposal might be ambitious, but I argue there are good reasons to consider it as one building block of a (distributively) just future for life on Earth.