Deep-time Major Biological and Climatic Events Versus Global Changes: Progresses and Challenges

Climate changes are altering Earth's biodiversity in very complex ways while predicting the evolutionary trajectories of Earth's ecosystem response to the current global changes is highly challenging. The Earth has witnessed multiple climate extremes associated with profound perturbations in the global carbon cycle since the formation of modern ecosystems 540 million years ago. Unraveling the triggering and terminating mechanisms, the environmental perturbations, and the associated biological responses to these climate extremes can provide a basis to anticipate and manage the responses of biodiversity to the current changing climates. However, these efforts have been hampered by major challenges concerning the vast differences in the time scales of deep-time and modern ecosystem changes, the lack of high-resolution and reliable environmental proxy data (temperature, CO2, precipitation, ocean redox conditions, etc.), and the missing of high-resolution marine and terrestrial biodiversity curves. Therefore, those challenges bring a huge gap in comparison between current global changes and the deep-time archives. Although the Earth has been in greenhouse conditions for most of the past 540 million years (i.e., where the poles were ice-free), there were numerous climate extremes such as glaciations and hyperthermal events. Unfortunately, the relationships between major biological revolutions (extinctions and radiations) and climatic events in deep time are more complex than expected. For instance, biodiversity exhibited a steady increase during the Early Ordovician cooling, the Late Paleozoic Ice Age, the Late Cenozoic Ice Age, and the greenhouse intervals from the Middle-Late Triassic and Cretaceous. In contrast, biodiversity underwent rapid decline during the rapid cooling of the Late Ordovician glaciation and during the rapid warming periods associated with volcanic CO2 degassing at the end of the Permian, the end of the Triassic, and the end of the Cretaceous. The different response patterns of biodiversity to climate changes in deep-time led us to realize that the fundamental driving factors of biodiversity change may not simply be the background values of environmental factors such as temperature and CO2, but what really matters is the rate of environmental change. Specifically, when the rate of environmental change is small, namely, the environment is relatively stable, organisms have enough time to adapt to environmental changes and biodiversity will not be lost or even undergo flourish; on the contrary, if the rate of environmental change is too sharp, exceeding the tipping point for the ecosystems, organisms do not have enough time to adapt and biodiversity will be significantly reduced and even lead to mass extinctions. The limited deep-time carbon emission data from numerical models suggest that the present-day CO2 emission rate exceeded any intervals during major extinction events in geological history. Therefore, avoiding environmental catastrophes and mass extinctions against future impacts has become a top priority. Here, we propose integrated multidisciplinary research through breaking multi-layer boundaries of the Earth, and carrying out comparative studies of deep-time and modern geological records, glacial and hyperthermal climates, marine and terrestrial ecosystems, and long-term and short-term time scales. Simulating interactions between biological and environmental events by establishing deep-time Earth system models is also a clear avenue to go. Those integrative studies will bring essential constraints for the prediction of the impact of climatic perturbations on future biodiversity trajectories, which is critical given the current concerns about the consequences of the ongoing 6th mass extinction. These are also important directions for Earth system science studies in the future.