diff --git a/docs/earth_spheres.md b/docs/earth_spheres.md
index a4d69d72..80d74956 100644
--- a/docs/earth_spheres.md
+++ b/docs/earth_spheres.md
@@ -19,6 +19,6 @@ Spheres dividing planet Earth into subsystems, which are collectives of (physica
 - Anthroposhere
 
 ### Sources
-- Hugget, R. et al, 2024, DOI: 10.1177/03091333241275465
-- Guth, P, et al, 2021, https://doi.org/10.3390/rs13183581
-- Martin, Y.E, et al 2012
+- Hugget, R., et al, 2024, DOI: 10.1177/03091333241275465
+- Guth, P., et al, 2021, https://doi.org/10.3390/rs13183581
+- Martin, Y.E, et al, 2012