Earth in Time

The geomagnetic field is one of the most ancient features of our planet—at least 3.4 billion years old. The geomagnetic field is thought to be essential for life because it keeps the solar wind from stripping away the atmosphere. As Earth’s core cools, the solid inner core freezes, releasing latent heat and gravitational energy, thus producing the magnetic field. However, this process presents a profound challenge to our understanding. If the core loses heat at the rate necessary to produce the magnetic field, as we go back in time, the core rapidly becomes so hot that inner core freezing is no longer possible. The inner core may only be 1 billion years old, leaving most of the paleomagnetic record unexplained by inner core freezing. Recent mineral physics determinations point to a core that has a higher thermal conductivity than previously thought, a result that pushes the age of the inner core even younger. If not via inner core freezing, how was the magnetic field produced over most of geologic history?

The Earth is the only planet with well-defined plate boundaries whose motions and evolution frame nearly all geological phenomena and provides basic controls on Earth’s atmosphere and oceans. There is a lack of fundamental understanding of when plate tectonics developed on the Earth, why on Earth and not elsewhere, the interconnections with elemental cycling on the Earth (see question 3), and the processes that explain how it developed. New instruments, emerging fields, experimental investigations, computational advances, and imaging and modeling will be crucial to answering questions about plate tectonics.

More than 5,000 known minerals, as well as many yet to be discovered, hold the chemical diversity and history of the Earth. Minerals, along with associated melts and fluids, host and transport critical elements that are essential for geologic processes. Critical elements are defined as those that: (1) have created suitable conditions for biological activity; and (2) provide the raw ingredients for materials essential to the functioning, prosperity, and security of modern society, such as low-carbon or carbon-free energy and elements for electronics, defense, medicine, and advanced manufacturing. These elements are concentrated in certain parts of the Earth by processes that geoscientists are beginning to understand on a planetary scale.

The distribution of critical elements is determined by the processes that have influenced element cycling between Earth’s interior and surface environments throughout Earth’s history. Ongoing, present-day processes continue to redistribute critical elments.

Recent observations show that earthquake rupture is not simple and that deformation of the Earth occurs over a broad range of spatial and temporal scales. For example, recent earthquake ruptures have expressed exceptional geometric complexity and dramatic improvements in monitoring have led to discoveries of a far broader specturm of slow, transient deformation than represented by ordinary earthquakes.

We know the form of the equations governing deformation but not the flow laws that govern the relevant material properties for deformation. The promise of the coming decade is that advances in characterizing material properties, coupled with high-performance computing to carry out increasingly accurate simulations of crust, lithosphere, and mantle deformation processes, will lead to a more fundamental understanding of the full spectrum of observed deformation.

Volcano science is poised to supply answers via physics-based models for all key processes driving eruptions, taking advantage of a wealth of data from eruption observations on fine temporal and spatial scales and the emerging ability to process data extremely rapidly. In addition, new time-sensitive geophysical imaging techniques and micro-scale geochemical clocks provide unmatched information about the speed of rising magma in the crust and mantle, and how the geometries of storage regions and transport pathways of volcanoes evolve and influence eruptions.

Geoscientists are on the cusp of being able to use these approaches during eruptions to provide urgently needed advice to response agencies in near-real time.

Great progress over the past two decades has been made in linking climate, tectonics, and erosion processes to understand how they shape and are dynamically influenced by Earth’s surface topography. This process has brought into focus key scientific questions concerning the role of rock mechanical properties, short-term actors such as storms, the rheology and dynamics of Earth’s interior in landscape evolution, and the co-evolution of landscapes with the atmosphere, cryosphere, sea level, and life. Quantifying topographic change is crucial to advance many areas of geoscience—from understanding Earth-system interactions over geologic time, to predicting landslides, ecosystem gradients, and the distribution of freshwater and soil resources in the coming decades. In the next decade, a community goal is to reach sub-meter resolution in modern topography for much of the globe.

The critical zone is the reactive skin of the terrestrial Earth, extending from the top of the vegetation through the soil and down to the fresh bedrock and the bottom of actively cycling groundwater. Research on the critical zone has enabled studies of water, nutrient, and carbon cycles, and connections between vegetation and deep subsurface processes. Because the structure and reactivity of the critical zone influences moisture, groundwater, energy, and gas exchanges between the land and atmosphere, it exerts a key role in modulating atmospheric concentrations of greenhouse gases (particularly water vapor and carbon dioxide) and, therefore, temperature.

Humans have become geologic agents. Changes that required thousands to millions of years to occur in the Earth are integral to providing deep and compelling scientific context to the challenges faced by human society in the face of rapidly increasing rates and magnitudes of climate and environmental change. Evidence of both long-term and rapid environmental change in Earth’s history—from the ancient past to the present—provides key baselines for comparison to modern change, helps to elucidate Earth system dynamics, and plays a critical role in the calibration of physical models that are used to project future scenarios.

Emerging cyberinfrastructure that archives and analyses paleoclimate datasets can now be leveraged to address fundamental questions about climate dynamics. Improved capacity to conduct continental scientific drilling projects or those that cross the land-sea interface could facilitate the development of targeted field programs to recover longer, continuous records of climate variability and/or to increase the spatial and temporal density of observations.

The water cycle is necessary for all terrestrial life, and there is now increased urgency to understand changes in the water cycle due to the influence of people and climate change. Earth science has a particularly critical role in advancing fundamental knowledge of the water cycle and how it integrates with other physical, biological, and chemical processes in the Earth system.

Impacts of climate change on the water cycle and the associated ramifications for civilization motivate much of contemporary hydrology. Of particular interest are the ways in which climate change will affect the nature and frequency of extreme events like droughts, floods, fires, and the attendant impacts on human populations. There is also growing recognition of the inseparability of the water cycle and human activity. The dynamic integration of hydrologic and human systems is therefore increasingly important in hydrologic modeling. Substantial water will be required for future food and energy production, but it is unclear whether water availability can meet the demand.

To date, the Earth is the only known planet with an active biosphere. This biosphere has evolved and interacted with the chemical makeup of Earth’s surface for billions of years. Biological processes that cycle carbon, oxygen, nitrogen, sulfur, and other elements and influence the global chemistry and mineral diversity of Earth’s surface include photosynthesis, microbially-catalyzed weathering and mineral formation, and the production of biogenic greenhouse gases such as carbon dioxide and methane. The next decade will bring advances in the mechanistic understanding of biological contributions to these biogeochemical cycles and the history of the Earth as a habitable planet.

Biodiversity at any point in time and space reflects the net balance between the formation and loss of species and their biological traits through speciation, extinction, and change within species. The study of biodiversity is therefore inseparable from the study of evolutionary rates, as well as the timing and rate of geological processes that shape the environments in which evolution occurs.

The relationships between biodiversity and geological processes, which include large-scale human activities, is considered to be reciprocal; and understanding how and why diversity varies over time, environment, and geography is central to many Earth-life interactions and feedbacks.

Geohazards (earthquakes, tsunamis, volcanic eruptions, landslides, and flooding) caused between $6.5 trillion and $14 trillion in damage and approximately 8 million fatalities between 1900 and 2015. The severity of impacts is increasing rapidly as risk mitigation fails to keep up with increasing exposure. Improved collaboration with many other disciplines, including engineering, data science, disaster psychology, health sciences, land use planning, and government policy is required to reduce risk; however, a predictive and quantitative understanding of geohazards by Earth scientists is foundational to all such efforts.