The origin and rise of complex life: progress requires interdisciplinary integration and hypothesis testing

Abstract

Understanding of the triggers and timing of the rise of complex life ca 2100 to 720 million years ago has expanded dramatically in recent years. This theme issue brings together diverse and novel geochemical and palaeontological data presented as part of the Royal Society ‘ The origin and rise of complex life: integrating models , geochemical and palaeontological data ’ discussion meeting held in September 2019. The individual papers offer prescient insights from multiple disciplines. Here we summarize their contribution towards the goal of the meeting; to create testable hypotheses for the differing roles of changing climate, oceanic redox, nutrient availability, and ecosystem feedbacks across this profound, but enigmatic, transitional period.

Oxygen suppression of macroscopic multicellularity

“…Indeed, snowflake yeast evolve a 4.5-fold increase in maximum cluster size over just 145 days (radius of the 95th percentile ancestor = 39.8 µm, radius of the 95th percentile day-145 supplemental oxygen = 180 µm), a miniscule interval with respect to geologic time. Ongoing research into the state and dynamics of early Earth surface environments, together with an inclusive consideration of evolutionary trade-offs, is thus a particularly exciting avenue for discovering how environmental constraints may have acted to shape the evolution of complex multicellular life 13,[25][26][27][28]31,72,73 .…”

“…The abrupt radiation of macroscopic multicellularity in the Ediacaran oceans coincides with evidence for a global rise in oceanatmosphere oxygen levels (~800-550 Ma) 12,[22][23][24] . Although this geobiological observation is largely undisputed, the role of oxygen in the evolution of macroscopic multicellularity remains a topic of intense debate [25][26][27][28][29] .…”

Evolution of a key enzyme of aerobic metabolism reveals Proterozoic functional subunit duplication events and an ancient origin of animals

“…At that time, Earth was colonized mainly by microbial lifeforms, and representative species of only a few microbial clades are preserved in the fossil record. Moreover, the interpretation of these early eukaryote fossils is challenging because their key distinguishing characteristics, such as organelles and nuclei, do not preserve well 54 . Our findings for the emergence of eukaryotic NAD-IDH during the Paleoproterozoic is in agreement with contemporary molecular clock estimates for eukaryotes emergence 32 , 33 and for the canonical view that stem and crown-group eukaryotes may have emerged early in the Proterozoic, keeping low diversity levels in restricted environments until a late Mesoproterozoic diversification 55 – 57 .…”

The Nitrogen Cycle in an Epeiric Sea in the Core of Gondwana Supercontinent: A Study on the Ediacaran-Cambrian Bambuí Group, East-central Brazil

“…In addition to this, δ 15 N bulk points out that as expected in such a situation, the N-cycle (and hence redox conditions) functioned with a reduced nitrate pool, which could have contributed to hinder the sustainability of complex forms of life. The link between oxygenation and the Cambrian explosion has been discussed for more than 60 yr (e.g., Nursall, 1959;Wood et al, 2020). Metazoans can indeed habit environments with low oxygen concentrations and some studies even suggest that the amount of O 2 necessary for their metabolism was achieved much earlier than the first appearance of animals on the fossil record (e.g., Mills et al, 2014).…”