Lidya G. Tarhan

• PhD
• PostDoc Position at Yale University

The processes responsible for the fossilization of the Ediacara Biota—Earth's earliest fossil record of communities of complex, multicellular organisms—have long been debated. On the basis of both geologic and experimental investigations, recent studies have proposed that early diagenetic silica cementation may have been pivotal to the moldic prese...

The earliest evidence of complex macroscopic life on Earth is preserved in Ediacaran‐aged siliciclastic deposits as three‐dimensional casts and molds, known as Ediacara‐style preservation. The mechanisms that led to this extraordinary preservation of soft‐bodied organisms in fine‐ to medium‐grained sandstones have been extensively debated. Ediacara...

Elevated temperatures persisted for an anomalously protracted interval following pulsed volcanic carbon release associated with the end-Permian mass extinction, deviating from the expected timescale of climate recovery following a carbon injection event. Here, we present evidence for enhanced reverse weathering—a CO2 source—following the end-Permia...

The evolution of oxygen cycles on Earth’s surface has been regulated by the balance between molecular oxygen production and consumption. The Neoproterozoic–Paleozoic transition likely marks the second rise in atmospheric and oceanic oxygen levels, widely attributed to enhanced burial of organic carbon. However, it remains disputed how marine organi...

The relative proportions of carbon, nitrogen, and phosphorus, commonly referred to as the Redfield ratio (106:16:1), have likely varied dramatically through Earth’s history in response to changes in oceanic redox state and nutrient availability. However, there have been few attempts to track long-term secular patterns in the elemental stoichiometry...

The early Paleozoic emergence of bioturbating (sediment-dwelling and -mixing) animals has long been assumed to have led to substantial changes in marine biogeochemistry, seafloor ecology, and the preservation potential of both sedimentary and fossil archives. However, the timing of the rise of bioturbation and environmental patterns in its expansio...

Calcium carbonate formation is the primary pathway by which carbon is returned from the ocean–atmosphere system to the solid Earth1,2. The removal of dissolved inorganic carbon from seawater by precipitation of carbonate minerals—the marine carbonate factory—plays a critical role in shaping marine biogeochemical cycling1,2. A paucity of empirical c...

Earth’s earliest fossils of complex macroscopic life are recorded in Ediacaran-aged siliciclastic deposits as exceptionally well-preserved three-dimensional casts and molds, known as “Ediacara-style” preservation. Ediacara-style fossil assemblages commonly include both macrofossils of the enigmatic Ediacara Biota and associated textural impressions...

The primary mineralogy of marine carbonates has varied over geological time in concert with the secular evolution of global climate and seawater chemistry. Here, we employed a multi‐proxy geochemical and petrographic approach, including measuring the Ca isotope (δ⁴⁴Ca) and Sr content of Ediacaran–Cambrian carbonates, to provide new insights into th...

In the absence of complex, bioturbating organisms, the seafloor during the Precambrian was covered in widespread organic matgrounds. The greatest diversity and complexity of organic mat textures occur in the Ediacaran fossil record as exemplified by the Ediacara Member of the Rawnsley Quartzite, which crops out in and around the Flinders Ranges, So...

The Ediacara Biota, Earth’s earliest ecosystems of complex, macroscopic, multicellular organisms, is preserved in terminal Ediacaran strata worldwide. In the Ediacara Member of South Australia, Ediacara fossil assemblages occur in intimate association with macroscopic, iterative organosedimentary structures, known as “textured organic surfaces” (TO...

The abundance and fractionation of the stable strontium (Sr) isotope system are being increasingly utilized to move forward our understanding in geological and cosmological processes. Two analytical techniques are commonly used to measure stable Sr isotopes: 1) double-spike thermal ionization mass spectrometry (DS-TIMS) and 2) Zr-doped sample-stand...

Marine dissolved organic carbon (DOC), the largest pool of reduced carbon in the oceans, plays an important role in the global carbon cycle and contributes to the regulation of atmospheric oxygen and carbon dioxide abundances. Despite its importance in global biogeochemical cycles, the long-term history of the marine DOC reservoir is poorly constra...

Bioturbation—sediment mixing and ventilation by burrowing animals—provides one of the most prominent examples of how animals shape their surroundings. A critical but longstanding question is when and how in Earth's history bioturbators began to similarly influence marine biogeochemistry. Recent work has proposed that even though the development of...

Carbonate zinc (Zn) isotopes have increasingly been used to track changes in seawater Zn isotopic composition. A large body of recent work, in particular studies conducted under the GEOTRACES program, have added significantly to our knowledge of how Zn behaves in the water column. However, our understanding of how water-column Zn isotopic signals b...

Casts and molds of soft-bodied organisms in Ediacaran sandstones ("Ediacara-style" fos-silization) have played an important role in reconstruction of the emergence and radiation of early complex macroscopic life. However, the preservational processes responsible for the Ediacara fossil record are still vigorously debated. Whereas classic studies pr...

The Precambrian Ediacara Biota-Earth's earliest fossil record of communities of macroscopic, multicellular organisms-provides critical insights into the emergence of complex life on our planet. Excavation and reconstruction of nearly 300 m2 of fossiliferous bedding planes in the Ediacara Member of the Rawnsley Quartzite, at the National Heritage Ed...

An amendment to this paper has been published and can be accessed via a link at the top of the paper.

The marine phosphorus cycle plays a critical role in controlling the extent of global primary productivity and thus atmospheric pO2 on geologic time scales. However, previous attempts to model carbon–phosphorus-oxygen feedbacks have neglected key parameters that could shape the global P cycle. Here we present new diagenetic models to fully paramete...

Many infaunal marine invertebrates produce mucus excretions that play an important role in metal binding, authigenic mineralization and burrow stabilization. To date, only a handful of studies have characterized the functional groups that control the surface reactivity of burrow linings and backfills. This makes it difficult to place estimates on t...

The diversification of metazoans during the latest Neoproterozoic and early Cambrian has been attributed to, among other factors, a progressive rise in surface oxygen levels. However, recent results have also questioned the idea of a prominent rise in atmospheric oxygen levels or a major or unidirectional shift in the marine redox landscape across...

The Ediacara Biota, Earth's earliest communities of complex, macroscopic, multicellular organisms, appeared during the late Ediacaran Period, just prior to the Cambrian Explosion. Ediacara fossil assemblages consist of exceptionally preserved soft-bodied forms of enigmatic morphology and affinity which nonetheless represent a critical stepping-ston...

Bioturbation, the physical and chemical mixing of sediments by burrowing animals, is a critical engineering process in modern seafloor environments and exerts an important control on not only benthic ecology and sediment properties but also ocean-wide biogeochemical cycling. Well-mixed sediments have long been assumed to appear at the Precambrian–C...

The paleoenvironmental setting in which the Ediacara Biota lived, died, and was preserved in the eponymous Ediacara Member of the Rawnsley Quartzite of South Australia is an issue of long-standing interest and recent debate. Over the past few decades, interpretations have ranged from deep marine to shallow marine to terrestrial. One of the key feat...

Trace fossils from the Ediacaran–Cambrian transition of Brazil point to the existence of bioengineering meiofaunal animals prior to the ‘Cambrian Explosion’.

Patterns of origination and evolution of early complex life on this planet are interpreted largely from the fossils of the Precambrian soft-bodied Ediacara Biota. Excavation and reconstruction of beds of the Ediacara Member of the Rawnsley Quartzite at the National Heritage Ediacara fossil site Nilpena, in the Flinders Ranges of South Australia has...

The evolutionary trajectory of early complex life on Earth is interpreted largely from the fossils of the Precambrian soft-bodied Ediacara Biota, which appeared and evolved during a time of dynamic biogeochemical and environmental fluctuation in the global ocean. The Ediacara Biota is historically divided into three successive Assemblages—the Avalo...

Fossils preserving the anatomy of soft tissues provide rare but essential evidence for the reconstruction of metazoan evolutionary history. Decay is inherent to the fossilization process and features may be distorted, displaced, or missing even in exceptionally preserved fossils, and non-anatomical artifacts may be introduced. Here we describe the...

The Ediacara Member of the Rawnsley Quartzite of South Australia hosts some of the most ecologically and taxonomically diverse fossil assemblages of the eponymous Ediacara Biota-Earth's earliest fossil record of communities comprised of macroscopic, complex, multicellular organisms. At the National Heritage Site, Nilpena, fifteen years of systemati...

The Ediacara Biota, Earth’s earliest fossilized ecosystem of complex, macroscopic, multicellular organisms, occurs in terminal Ediacaran strata worldwide, yet how the fossils are preserved remains controversial. Ediacara assemblages consist of exceptionally preserved soft-bodied forms of enigmatic morphology and phylogenetic affinity. Many of these...

The Cambrian has long been regarded as a time of dynamic morphological innovation and ecological expansion for a wide range of epibenthic and pelagic metazoan clades. Less well documented, however, is the extent to which infaunal organisms participated in this 'Cambrian Explosion' and particularly the extent to which the infaunal lifestyle, infauna...

The Ediacara Biota, Earth's earliest fossilized ecosystem of complex, macroscopic, multicellular organisms, occurs in terminal Ediacaran strata worldwide, yet how the fossils are preserved remains controversial. Ediacara assemblages consist of exceptionally preserved soft-bodied forms of enigmatic morphology and phylogenetic affinity. Many of these...

Continental siltstones of the Mesoproterozoic Copper Harbor Formation, Michigan contain macroscopic structures of a size and morphological complexity commonly associated with fossils of eukaryotic macroorganisms. A biogenic origin for these structures would significantly augment the Proterozoic continental fossil record, which is currently poor, an...

Discoidal macrofossils reported herein from the lower Cambrian Zabriskie Quartzite (Great Basin, western United States) record the oldest Phanerozoic medusozoan body fossils, as well as the oldest medusozoan stranding event on record. Moreover, these fossils provide evidence of a significant shift in the taphonomic mode characteristic of preservati...

Seagrass meadows are a key component of marine ecosystems that play a variety of prominent geobiological roles in modern coastal environments. However, seagrass itself has low preservation potential, and consequently seagrass meadows are hard to identify in the rock record. In this study we combine observational taphonomic data from a modern sparse...

Problematic fossils, extinct taxa of enigmatic morphology that cannot be assigned to a known major group, were once a major issue in palaeontology. A long-favoured solution to the 'problem of the problematica', particularly the 'weird wonders' of the Cambrian Burgess Shale, was to consider them representatives of extinct phyla. A combination of new...

The Ediacara Biota, Earth’s earliest complex, macroscopic, multicellular ecosystem, is preserved in terminal Ediacaran strata worldwide, deposited in the wake of the ‘Snowball Earth’ glaciations and just prior to the Cambrian Explosion. Ediacara fossil assemblages consist of exceptionally preserved soft-bodied forms of enigmatic morphology, ecology...

Oxygenation has widely been viewed as a major factor driving the emergence and diversification of animals. However, links between early animal evolution and shifts in surface oxygen levels have largely been limited to extrapolation of paleoredox conditions reconstructed from unfossiliferous strata to settings in which contemporaneous fossils were p...

The transition to the diverse and complex biosphere of the Ediacaran and early Paleozoic is the culmination of a complex history of tectonic, climate, and geochemical development. Although much of this rise occurred in the middle and late intervals of the Neoproterozoic Era (1000–541 million years ago [Ma]), the foundation for many of these develop...

Bioturbation, the physical and chemical mixing of sediment by burrowing animals, exerts an important control on the character of modern marine sediments and biogeochemical cycling. Here we show that the mixing of sediments on marine shelves remained limited until at least the late Silurian, 120 million years after the Precambrian-Cambrian transitio...

The paleoenvironmental setting in which the Ediacara Biota lived, died and was preserved in the eponymous Ediacara Member of the Rawnsley Quartzite of South Australia is an issue of longstanding interest and recent debate. Over the past few decades, interpretations have ranged from deep marine to shelfal to intertidal to terrestrial. Here we examin...

The radiation of burrowing metazoans in the early Phanerozoic dramatically altered the properties of marine sediment, an event commonly referred to as the “Cambrian substrate revolution” or “agronomic revolution.” The advent of infaunalization, and especially biogenically-mediated sediment mixing, profoundly impacted the development of Phanerozoic...

The affinity of the Ediacaran fossil Shaanxilithes ningqiangensis and putatively related forms has long been enigmatic; over the past few decades, interpretations ranging from trace fossils to algae to metazoans of uncertain phylogenetic placement have been proposed. Combined morphological and geochemical evidence from a new occurrence of S. ningqi...

Instances of exceptional preservation-preservation of near-surface structures of high taphonomic fidelity, including bioglyphic detail-have been previously reported from Cambro-Ordovician trace fossil assemblages worldwide. However, it has hitherto been unknown to what extent this exceptional preservation characterises the Cambro-Ordovician record...

Microbialites are the most abundant macrofossils of the Precambrian. Decline in microbialite abundance and diversity during the terminal Proterozoic and early Phanerozoic has historically been attributed to the concurrent radiation of complex metazoans. Similarly, the apparent resurgence of microbialites in the wake of Paleozoic and Mesozoic mass e...

Tarhan, L.G., Jensen, S. & Droser, M.L. 2011: Furrows and firmgrounds: evidence for predation and implications for Palaeozoic substrate evolution in Rusophycus burrows from the Silurian of New York. Lethaia, Vol. 45, pp. 329–341. The Silurian Herkimer Formation of east-central New York contains abundant, exceptionally preserved composite Rusophycus...

Earth's earliest known metazoan ecosystems are represented by a handful of globally distributed fossil assemblages, collectively referred to as the Ediacara Biota. Although a number of these deposits have been extensively studied, a large proportion of Ediacaran diversity remains uncharacterized. As a result, our understanding of community structur...