The 50th anniversary of Geology provides not only a welcome occasion to celebrate past decades of extraordinary advances in geoscience knowledge but also the impetus to cast our gaze forward and envision what new directions and discoveries will guide geoscience research through the next 50 years and beyond. My research broadly concerns reconstructing the factors that have shaped the emergence and evolution of complex life on our planet, as well as the fidelity of archives of past environmental and ecological change. This is an area that, in my view, is currently undergoing a renaissance—fueled by efforts leveraging multidisciplinary approaches; exploring increasingly highly resolved spatial and temporal scales; and harnessing the power of large, stratigraphically grounded data sets.

Many of our most pressing questions regarding Earth's early history concern interactions between past life and environments and how these have co-evolved. To address these questions, which are truly multidisciplinary in scope, we need a multidisciplinary toolkit. In recent years there have been major strides forward in the realm of combining paleontological, sedimentological, paleoclimatic, and geochemical approaches—particularly for the Neoproterozoic and lower Paleozoic eras, the interval bracketing the emergence and initial radiations of complex animal life. Geochemical and paleontological investigations of this interval, in particular, have historically occurred within disciplinary silos, even when motivated by questions centered on environmental-biotic feedbacks. Paleontological and geochemical data sets have commonly been collected from different units, facies, and even paleocontinents. For instance, many paleoredox proxy records, such as iron speciation, sulfur isotopes, and trace element analyses, are generated from muddy lithologies that are particularly susceptible to diagenesis and weathering and thus more tractably sampled from drill core than outcrop (Ahm et al., 2017). In contrast, certain body and trace fossils more commonly occur or are more readily recognized in non-muddy lithologies, and their preservation in outcrop may even be accentuated by early diagenetic cementation, dolomitization, or preferential weathering (Savrda, 2012). Additionally, Neoproterozoic successions suffer from substantial chronostratigraphic uncertainties relative to younger intervals—compounded by a paucity of robust index fossils suitable for biostratigraphic correlation as well as lingering questions regarding the syngeneity and synchroneity of potential chemostratigraphic markers such as carbon isotope excursions (cf. Xiao et al., 2016). Integrating these disparate data sets on time scales that are ecologically and evolutionarily meaningful therefore remains a major hurdle. However, a growing body of studies that provide new chronostratigraphic constraints on key intervals in Earth's early life history (Pu et al., 2016; Rooney et al., 2020) and attempt to compile paleoenvironmental, paleoclimatic, biogeochemical, and paleontological data in tandem (Li et al., 2015; Wood et al., 2019) offers promise for future multidisciplinary efforts.

At the same time, higher-resolution data are clearly critical to addressing questions of biological-environmental interactions through this interval—in part because geochemical, paleontological, and geochronological proxies can all be subject to alteration. Bulk samples, as palimpsests of primary, diagenetic, metamorphic, and recent weathering processes (Hood et al., 2016; Tarhan et al., 2018), may not serve as faithful archives of seawater and sea-floor conditions. Additionally, recent work has highlighted that finer stratigraphic and spatial scales frequently correspond to the biological and ecological time scales of greatest interest. For instance, petrographic-scale geochemical analyses are shedding new light on short-term redox fluctuations in the Neoproterozoic seawaters inhabited by some of our earliest biomineralizing and potentially reef-forming complex organisms (Hood and Wallace, 2015; Wood et al., 2017). Application of both older and emerging microscale analytical techniques with the capability to target geologic and fossil materials at a truly granular scale—from cathodoluminescence microscopy and electron microprobe analyses to laser ablation and secondary ion mass spectrometry—provides a powerful toolkit to tackle both longstanding and emerging questions in Earth's early environmental and life history (Tarhan et al., 2016; Trower et al., 2021). Likewise, studies coupling fossil records with biogeochemical modeling are allowing us to reevaluate the feasibility of longstanding conceptual frameworks for environmentalbiotic coevolution. For instance, some of my recent work has used this approach to assess whether animals emerged against a backdrop of high seawater dissolved organic carbon levels (Fakhraee et al., 2021), or whether the expansion of well-bioturbated sediments drove shifts in marine productivity and oxygen concentrations (Tarhan et al., 2021). Direct integration of stratigraphic and modeling observations ensures that paradigms of early life-environment coevolution have been rigorously tested and are grounded in a mechanistic understanding of physical, chemical, and biological processes. Similarly, research seeking to quantitatively apply insights gleaned from modern natural and experimental geobiological systems (as well as sedimentary geochemical modeling of these systems) directly to the fossil record is shedding new light on the role of preservational processes (and their inherent biases) in shaping the fossil record (Slagter et al., 2021; Westacott et al., 2021).

Recent work has also highlighted the need to be clear-eyed when it comes not only to the extraordinary opportunities offered by burgeoning proxy-based geochemical and paleontological data sets but also their limitations. Statistical and probabilistic tools increasingly offer means to constrain confidence in these data sets and guide how we can use them to robustly reconstruct major trends in evolutionary and environmental history (Sperling et al., 2015; Anderson et al., 2018). And although few would dispute the imperfect nature of the stratigraphic and shelly fossil records (Sadler, 1981), we must not overlook that even extraordinary, Lagerstättengrade fossils have undergone decay and alteration—in fact, many pathways of exceptional preservation necessitate decay—and are shaped by taphonomic processes that can obfuscate original anatomical and ecological information and introduce morphological variability (Briggs, 2003). Exceptional fossils can undeniably yield exceptional insights into past life. However, as a community, we must continue to recognize that, if we hope to distinguish outliers from patterns truly representative of Earth's history, scrutiny of all components of the fossil record—body or trace, skeletal or soft-tissue—should be premised on characterization of extensive sample sets rather than isolated examples (Evans et al., 2017; Tarhan, 2018). And if our aim is to reconstruct how changing conditions across Earth's surface environments have shaped the evolutionary trajectory of life—and how, in turn, the emergence of new ecological novelties and innovations has engineered Earth's landscapes (cf. Erwin, 2015)—any consideration of fossil data must occur in a geologic context and be grounded in a paleoenvironmental and taphonomic framework.

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