Ocean Acoustics, Brain Organoids, and The End of Everything: Science Magazine Podcast Explores Ocean pH Sensing, Hominin Lead Exposure, and Cosmic Endings

Three science stories anchor this episode: acoustic methods to monitor ocean acidification, brain organoid research on lead exposure across modern humans and extinct hominins, and a deep dive into cosmic endings with Katie Mack. The ocean segment explains how borate chemistry and pH shift the way sound travels in seawater, and how hydrophones, autonomous floats, and fiber sensing could map these changes at scale. The brain-organoid segment reveals how archaic and modern FOXP2 variants respond differently to lead during neural development, hinting at language evolution. The cosmos segment surveys big crunch, heat death, big rip, vacuum decay, and bounce, and asks what these endings mean for humanity.

Episode Overview

This Science Magazine podcast, dated October 30, 2025, threads together three diverse but linked stories that highlight how physics, biology, and cosmology intersect with questions about Earth's future and humanity's past. The week’s conversations unfold with staff writer Paul Luson discussing sound as a proxy for ocean chemistry, a field test of brain organoids to probe ancient human biology, and a six-part series on the fate of the universe with cosmologist Katie Mack.

Segment 1 — Listening to the Ocean: Acoustic Approaches to pH Sensing

The first segment centers on the physics of sound in seawater and how it can inform measurements of ocean acidification. The discussion traces a process known as chemical relaxation, where borate in salted water shifts toward boric acid as pH changes, stealing energy from passing sound waves and slightly attenuating certain frequencies. By comparing a pH-sensitive borate system with an acid-neutral reference, researchers can infer pH changes from acoustic data. The conversation covers historical measurements from ships, the emergence of autonomous Argo floats that reach 2000 meters depth (and sometimes deeper), and the idea of using distributed acoustic sensing along fiber optic cables to monitor vast swaths of the ocean. These approaches aim to address the scale problem—how to sample an entire ocean column rather than a few surface points—and to provide long-term, high-resolution pH data that complement existing probes and floats. A key takeaway is that while ocean acidification is real, the impact on ocean noise and acoustic propagation is smaller than once feared, and can even become quieter with surface warming in the short term. The discussion also touches on how deep-water measurements could be integrated into moorings that monitor critical regions such as carbon-enhancement sites.

One guest, Paul Voosen, reflects on the late-2000s acoustical oceanography efforts, including navy-funded hydrophone deployments that tested the idea of acidification increasing ocean noise. A famous finding from 2009 suggested a detectable signal, but subsequent work over more than a decade has shown the effect to be modest, with potential implications that warming could alter how sound travels in ways that complicate straightforward pH readouts. The segment closes with questions about scale and feasibility, such as the potential of fiber sensing along cables to gather continuous data across large depths and regions, and how these acoustic measurements could ultimately serve as an efficient, noninvasive method to track ocean acidification across space and time. A notable takeaway is the multi-tool nature of ocean observation, combining hydrophones, autonomous floats, and emerging fiber-optic sensing to build a more complete picture of seawater chemistry.

"Not much. That, you know, that was like a big, that prompted a big surge of interest, and really was found to be a pretty small effect" - Paul Voosen, Earth climate and planetary science reporter at Science

Segment 2 — Brain Organoids and Lead Exposure Across Hominins

The second segment visits Allison Moultrie’s lab in San Diego where brain organoids are grown from stem cells to model developing neural tissue. The researchers use this system to investigate differences between modern humans and extinct relatives like Neanderthals and Denisovans, focusing on lead exposure during early development. The scientists identify a key gene, FOXP2, involved in language-related neural circuitry, and examine whether archaic versus modern versions of this gene produce different cellular responses when exposed to lead. A notable aspect of the work is their ability to engineer organoids carrying archaic or modern variants of NOVA1, FOXP2’s role as a master regulator of gene expression, and to expose these organoids to lead to observe the cellular consequences on neuronal migration, survival, and network formation. They report that neurons expressing the archaic version of FOXP2 show greater vulnerability to lead, particularly in neurons associated with language circuits, suggesting a potential link between genetic evolution, language development, and resilience to environmental toxins. The discussion also emphasizes limitations of organoids as models, including missing brain regions and circuitry relative to a whole organism, and references complementary work in mice where humanizing FOXP2 altered vocalization, supporting a broader link between gene variants and communication.

The researchers identify a small set of human-specific coding genes (about 61) that distinguish modern humans from Neanderthals and Denisovans, with FOXP2 among the standout examples. They generate organoids carrying either archaic or modern FOXP2 and assess lead’s impact across transcriptional and developmental programs. The results show that while many pathways respond similarly across variants, archaic FOXP2 can be more deleterious to FOXP2-expressing neurons, underscoring how subtle genetic shifts, combined with environmental exposure, could shape neural trajectories linked to language. A broader interpretation is that this approach integrates genetics, developmental neurobiology, and paleo-genomics to illuminate how our evolutionary path shaped brain function and vulnerability to toxins, offering a provocative lens on language evolution and resilience to pollutants.

"our FOXP2 expressing neurons do not die, so they're not that toxic to lead" - Allison Moultrie, Stanford Consortium

Segment 3 — The End of Everything: A Cosmic Guide to Universe Endings

The final segment frames Katie Mack’s exploration of the possible endings of the universe, based on her 2021 book The End of Everything, Astrophysically Speaking. Mack outlines five scenarios for the ultimate fate of the cosmos, each grounded in physics concepts such as dark energy, the cosmological constant, and gravitational dynamics. The big crunch contemplates a reversal of cosmic expansion, heating the universe as galaxies converge. Heat death envisions a universe driven to maximum entropy, where matter and energy are so diffuse that no events occur. The big rip posits phantom dark energy that tears apart structures at finite time, while vacuum decay considers a sudden shift in the vacuum state of space, changing fundamental physics. Finally, bounce cosmologies entertain cyclic or regenerating universes connected by gravitational waves or new Big Bangs. Mack notes that since her book’s publication, some data hints have suggested dark energy could be dynamic, though the cosmological constant remains a robust baseline. Still, the vacuum decay and bounce ideas persist as intriguing theoretical possibilities that could be tested with future observations, including gravitational waves and deep-field surveys. The discussion closes with philosophical reflections on life’s meaning against the vast timeline of the cosmos, acknowledging humanity’s apparent insignificance yet also the potential for discovery to redefine our place in the universe.

"The heat death model seems to be most consistent with the data at the moment" - Katie Mack, astrophysicist