Table S5.

Results of sensitivity analysis adding a range of biological forcing scenarios to a model with higher baseline O₂ level due to additional negative feedback

Feedback structure	Biology scenario	FOrg-C, mol/y	Δδ13C, ‰	ΔCO2, PAL	ΔO2, PAL	O2, PAL
		445 Ma	445 Ma	445 Ma	Peak*	Peak*
Original baseline	B (baseline)	4.1 × 1012	0 (0.03)	0 (17.2)	0	(0.23)
	E	5.1 × 1012	0.5	−0.6	0.11	0.34
	E + CP	6.1 × 1012	1.1	−1.5	0.27	0.50
	E + W	5.6 × 1012	0.7	−7.5	0.18	0.41
	E + CP + W	6.5 × 1012	1.2	−8.0	0.35	0.58
	E + W + F(i)	8.0 × 1012	2.2	−8.4	0.74	0.97
	E + CP + W + F(ii)	7.8 × 1012	2.1	−8.5	0.67	0.90
	E + CP + W + F(iii)	6.6 × 1012†	1.2†	−7.9†	0.72‡	0.97‡
(C/P)org = f(O2)	B (baseline)	6.1 × 1012	0.7	0.2	0.31	0.54
	E	6.6 × 1012	1.0	−0.6	0.38	0.61
	E + CP	7.3 × 1012	1.5	−1.2	0.49	0.72
	E + W	7.1 × 1012	1.2	−7.2	0.47	0.70
	E + CP + W	7.7 × 1012	1.6	−7.5	0.57	0.80
	E + W + F(i)	9.4 × 1012	2.9	−7.9	0.96	1.19
	E + CP + W + F(ii)	9.0 × 1012	2.5	−7.9	0.84	1.07
	E + CP + W + F(iii)	7.7 × 1012†	1.5†	−7.4†	0.92‡	1.17‡

^*Typically occurs during 430–415 Ma.

^†This is just before a sharp peak in F_Org-C and δ¹³C, and a sharp minimum in CO₂.

^‡Peak occurs at 407 Ma when baseline O₂ = 0.25 PAL.